No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Linking habitat specialization with species’ traits in European birds
Abstract
Ecological specialization provides information about adaptations of species to their environment. However, identification of traits representing the relevant dimensions of ecological space remains challenging. Here we endeavoured to explain how complex habitat specializations relate to various ecological traits of European birds. We employed phylogenetic generalized least squares and information theoretic approach statistically controlling for differences in geographic range size among species. Habitat specialists had narrower diet niche, wider climatic niche, higher wing length / tail length ratio and migrated on smaller distances than habitat generalists. Our results support an expected positive link between habitat and diet niche breadth estimates, however a negative relationship between habitat and climate niche breadths is surprising. It implies that habitat specialists occur mostly in spatially restricted environments with high climatic variability such as mountain areas. This, however, complicates our understanding of predicted impacts of climatic changes on avian geographical distributions. Our results further corroborate that habitat specialization reflects occupation of morphological space, when specialists depend more on manoeuvrability of the flight and are thus more closely associated to open habitats than habitat generalists. Finally, our results indicate that long distance movements might hamper narrow habitat preferences. In conclusion, we have shown that species’ distributions across habitats are informative about their positions along other axes of ecological space and can explain states of particular functional traits, however, our results also reveal that the links between different niche estimates cannot be always straightforwardly predicted.This article is protected by copyright. All rights reserved.
... Evidence is mixed for relationships between sensitivity and adaptive capacity at the species level. For example, habitat niche breadth of European breeding birds has been reported to be positively related to their dietary niche breadth and negatively related to their climatic niche breadth (Reif et al., 2016), while habitat niche breadth and climatic niche breadth were positively related in a study focussing on French breeding birds (Barnagaud et al., 2012). ...
... This suggests differences in this relationship between global and local scales, possibly influenced by our exclusion of migratory species from the analysis. Furthermore, we could not confirm a positive or negative relationship between climatic niche breadth and habitat niche breadth across avian species (Barnagaud et al., 2012;Reif et al., 2016), suggesting that these relationships differ between tropical assemblages with a high trait diversity compared with less diverse European bird assemblages (Barnagaud et al., 2012;Kissling et al., 2009;Reif et al., 2016). Together, this indicates that relationships between species' sensitivity and trait-based ecological adaptive capacity are context-dependent. ...
... This suggests differences in this relationship between global and local scales, possibly influenced by our exclusion of migratory species from the analysis. Furthermore, we could not confirm a positive or negative relationship between climatic niche breadth and habitat niche breadth across avian species (Barnagaud et al., 2012;Reif et al., 2016), suggesting that these relationships differ between tropical assemblages with a high trait diversity compared with less diverse European bird assemblages (Barnagaud et al., 2012;Kissling et al., 2009;Reif et al., 2016). Together, this indicates that relationships between species' sensitivity and trait-based ecological adaptive capacity are context-dependent. ...
Aim
How species respond to climate change is influenced by their sensitivity to climatic conditions (i.e. their climatic niche) and aspects of their adaptive capacity (e.g. their dispersal ability and ecological niche). To date, it is largely unknown whether and how species’ sensitivity to climate change and their adaptive capacity covary. However, understanding this relationship is important to predict the potential consequences of a changing climate for species assemblages. Here, we test how species’ sensitivity to climate change and trait‐based measures of their ecological adaptive capacity (i) vary along a broad elevational gradient and (ii) covary across a large number of bird species.
Location
A Neotropical elevational gradient (300–3600 m.a.s.l.) in the Manú Biosphere Reserve, south‐east Peru.
Methods
We focus on 215 frugivorous bird species along a Neotropical elevational gradient. We approximate species’ sensitivity to climate change by their climatic niche breadth, based on species occurrences across South America and bioclimatic variables. In addition, we use a trait‐based approach to estimate the dispersal ability of species (approximated by their wing pointedness), their dietary niche breadth (approximated by bill width) and their habitat niche breadth (the number of used habitat classes).
Results
We found that (i) species’ climatic niche breadth increased with elevation, while their trait‐based dispersal ability and dietary niche breadth decreased with elevation, and (ii) sensitivity to climate change and trait‐based adaptive capacity were not related across species.
Main conclusions
These results suggest different mechanisms of how species in lowland and highland assemblages might respond to climate change. The independent variation of species’ sensitivity to climate change and their trait‐based adaptive capacity suggests that accounting for both dimensions will improve assessments of species’ susceptibility to climate change and potential impacts of climate change on diverse species assemblages.
... Long-distance migration is thought to have evolved primarily in species able to utilise multiple habitat types [33][34][35] , which are encountered en route and in wintering areas. More generally, if migratory connectivity occurs at large scales, it could favour the selection for generalist traits. ...
... We found that species breeding origin niche was, on average, broader in long-distance trans-Saharan compared to intra-Palearctic migrants. Long-distance migration is generally thought to have evolved from ancestor species with broad habitat niches: individuals able to exploit a wider range of conditions during migration or www.nature.com/scientificreports/ at wintering grounds should be selectively advantaged over more specialised ones [33][34][35] . Empirical support for this hypothesis is limited 36,42,43 , and our data thus provide some additional evidence. ...
... Therefore, it is difficult to evaluate whether and to what extent our estimates of isotope niche breadth would have differed had we included wintering isotope signals. We used recently published data from Reif et al. 35 to examine the extent to which isotope niches from our sampled populations reflected diet specialisation and climate niche breadth reported at the species level. As expected, dietary isotopic niche did not match the breadth or diversity of consumed food items reported in the literature. ...
Naturally occurring stable isotope ratios in animal tissues allow estimation of species trophic position and ecological niche. Measuring multiple isotopes of migratory species along flyway bottlenecks offers the opportunity to sample multiple populations and species whose tissues carry information at continental scales. We measured δ 2 H, δ 18 O, δ 13 C, δ 15 N in juvenile feathers of 21 bird species captured at a migratory bottleneck in the Italian Alps. We examined if trends in individual isotopes reflected known migratory strategies and whether dietary (δ 13 C-δ 15 N) and spatially-explicit breeding origin (δ 2 H-δ 18 O) niche breadth (NB) differed among long-distance trans-Saharan (TS), short-distance (IP) and irruptive (IR) intra-Palearctic migrants, and whether they correlated with reported populations long-term trends. In both TS and IP groups, species δ 2 H declined with capture date, indicating that northern populations reached the stopover site later in the season, following a Type-I migration strategy. Values of δ 2 H indicated that breeding range of TS migrants extended farther north than IP and IR migrants. The breeding season was longer for IP migrants whose δ 13 C and δ 15 N values declined and increased, respectively, with time of capture. Average species dietary NB did not differ among migratory groups, but TS migrants displayed wider breeding origin niches, suggesting that long-distant migration is linked to broader ecological niches. Isotope origin NB well reflected species geographic range extent, while dietary NB did not correlate with literature accounts of species' diet. We found no relationship between species breeding NB and population trends in Europe, suggesting that conditions in the breeding grounds, as inferred by stable isotopes, are not the only determinant of species' long-term persistence. We demonstrate that ringing activities and isotopic measurements of passerines migrating through a bottleneck represents a unique opportunity to investigate large-scale life-history phenomena relevant to conservation. The concept of species' niche is a fundamental pillar of ecological science 1-3 , but remains challenging to quantify empirically. The challenge is particularly acute in the case of long-distance migratory birds due to the shifts in habitat use and distribution throughout their life cycles. Yet, habitat conditions in the breeding, stopover and wintering grounds profoundly influence individual fitness and demography of migratory populations. Long-distance migrants are showing rapid population declines and appear at greater risk of extinction compared to residents 4-6. Therefore, assessing niche parameters and differences among migratory groups can help in understanding the drivers shaping migration strategies and setting conservation actions. Migratory pathways of multiple species often overlap at stopover sites, which can represent bottlenecks, or passage points, causing high spatio-temporal concentration of many individuals and species from different migratory systems 7-9. Therefore, estimating niche parameters of individuals intercepted along migratory flyways may be a valuable and cost-effective approach to include multiple species potentially conveying information from large, continental scale, breeding areas 9-11 .
... Long-distance migration is thought to have evolved primarily in species able to utilise multiple habitat types (Levey and Stiles, 1992;Cresswell, 2014;Reif et al., 2016), which are encountered en route and in wintering areas. More generally, if migratory connectivity occurs at large scales, it could favour the selection for generalist traits. ...
... Because the relation between isotope niche measures and other estimates of species niche are still poorly understood (Shipley and Matich, 2020), we also examined whether our measures of dietary and origin isotope niches matched diet and climatic niche breadth derived from the literature and species range maps (Reif et al., 2016). While we expected estimates of spatially-explicit isotope origin niche to accord with species range maps, isotope dietary niche breadth is unlikely to match literature data. ...
... To compare empirical estimates of dietary and origin isotopic niche breadth with literature data, we used recently published measures of diet specialisation and climate niche breadth that were derived from literature data and breeding range maps of European birds (Reif et al. 2016). Diet specialisation was expressed as the coefficient of variation in the presence/absence of eight food types in the diet of each species (foliage, fruit, grain, insects, other invertebrates, terrestrial vertebrates, water vertebrates, carrion). ...
Naturally occurring stable isotope ratios in animal tissues allow estimation of species trophic position and ecological niche. Measuring multiple isotopes of migratory species along flyway bottlenecks offers the opportunity to sample multiple populations and species whose tissues carry information at continental scales.We measured δ2H, δ18O, δ13C, δ15N in juvenile feathers of 21 bird species captured at a migratory bottleneck in the Italian Alps.We examined if trends in individual isotopes reflected known migratory strategies and whether dietary (δ13C-δ15N) and spatially-explicit breeding origin (δ2H-δ18O) niche breadth (NB) differed among long-distance trans-Saharan (TS), short-distance (IP) and irruptive (IR) intra-Palearctic migrants, and whether they correlated with reported populations long-term trends.In both TS and IP groups, species δ2H declined with capture date, indicating that northern populations reached the stopover site later in the season, following a Type-I migration strategy. Values of δ2H indicated that breeding range of TS migrants extended farther north than IP and IR migrants. The breeding season was longer for IP migrants whose δ13C and δ15N values declined and increased, respectively, with time of capture.Average species dietary NB did not differ among migratory groups, but TS migrants displayed wider breeding origin niches, suggesting that long-distant migration is linked to broader ecological niches. Isotope origin NB well reflected species geographic range extent, while dietary NB did not correlate with literature accounts of species’ diet. We found no relationship between species breeding NB and population trends in Europe, implying that conditions in the wintering grounds could be more important for the long-term persistence of species.We demonstrate that isotopic measurements of passerines migrating through a bottleneck represents a unique opportunity to investigate large-scale life-history phenomena relevant to conservation.
... High mountain areas are subject to strong seasonal fluctuations (Lloret 2017) and species inhabiting these particular environments have evolved complex life-history strategies to cope with extreme abiotic conditions, generally exhibiting a high degree of habitat specialisation (Reif et al. 2016). Considering Hutchinson's representation of a species' ecological niche as an n-dimensional space, where the axes correspond to environmental variables or resources (Hutchinson 1957), habitat specialisation can be defined as the breadth occupied by a species on niche axes (Vamosi et al. 2014). ...
... The concept of ecological specialisation is, however, versatile and dependent on the spatial and seasonal scales at which it is evaluated (Devictor et al. 2010). In their work on habitat specialisation and traits in European breeding birds, Reif et al. (2016) suggested that, at large spatial scales, species can be habitat specialists but have a wide diet niche within the selected habitat. As for seasonal scales, in frugivorous birds, species that are highly specialised within a season might show a certain degree of flexibility across seasons in order to, for example, respond to resource fluctuations (Bender et al. 2017). ...
... Thus, this pattern of snowfinch flexibility seems to be space-sensitive and has a stronger effect at larger scales than at small ones. This result seems to be in accordance with Reif et al. (2016), who found a positive correlation between habitat specialisation and diet specialisation, but the relationship was weak at a coarse spatial scale. ...
... High mountain areas are subject to strong seasonal fluctuations (Lloret 2017) and species inhabiting these particular environments have evolved complex life-history strategies to cope with extreme abiotic conditions, generally exhibiting a high degree of habitat specialization (Reif et al. 2016). Considering Hutchinson's representation of a species' ecological niche as an n-dimensional space, where the axes correspond to environmental variables or resources (Hutchinson 1957), habitat specialization can be defined as the breadth occupied by a species on niche axes (Vamosi et al. 2014). ...
... The concept of ecological specialization is, however, versatile and dependent on the spatial and seasonal scales at which it is evaluated (Devictor et al. 2010). In their work on habitat specialization and traits in European breeding birds, Reif et al. (2016) suggested that, at large spatial scales, species can be habitat specialists but have a wide diet niche within the selected habitat. As for seasonal scales, in frugivorous birds, species that are highly specialized within a season might show a certain degree of flexibility across seasons in order to, for example, respond to resource fluctuations (Bender et al. 2017). ...
... Thus, this pattern of Snowfinch flexibility seems to be space-sensitive and to have a stronger effect at larger scales than at small ones. This result seems to be in agreement with Reif et al. (2016), who found a positive correlation between habitat specialization and diet specialization, but the relationship was weak at a coarse spatial scale. ...
High mountain areas are subject to strong seasonal fluctuations and species inhabiting these particular environments show a high degree of habitat specialisation to cope with extreme abiotic conditions. Estimates of habitat use are influenced by the spatial and seasonal scales at which they are evaluated, so studies at multiple scales are important in order to explore adaptive responses to seasonal environments. In the present study, we assessed habitat use of the White‐winged Snowfinch Montifringilla nivalis subsp. nivalis (henceforth Snowfinch) during breeding and non‐breeding seasons at three different spatial scales (diameters of 100 m, 250 m and 500 m). Although Snowfinches clearly used high‐elevation habitats in both seasons, there was evidence that they are less specific during the non‐breeding period: the variance explained by habitat and topographic factors was lower in winter compared to the breeding season. Moreover, our results suggest that the use of habitat is scale‐dependent. This pattern was especially relevant in the breeding season, perhaps because habitat use might be more related to nest site selection and specific foraging sites to provide food for nestlings. Snowfinches use high mountain habitats throughout the year, probably as a consequence of physiological and morphological specialisations typical of high‐elevation species, but in winter they show a certain flexibility in habitat use. Snowfinches might thus adopt a flexible specialist strategy. This could represent trade‐off to overcome possible effects on survival, condition and fitness, which can be particularly strong in harsh, unpredictable environments.
... Diversity patterns arise as a combination of individual species into communities, which differ in number of co-occurring species (Lennon et al., 2003). As those species are also differently specialised for biotopes (Reif et al., 2016), local avian communities differ in habitat specialization structure, some being on average more specialized than others (Julliard et al., 2006). From a conservation perspective, habitat specialization is a key predictor of population decline (Julliard et al., 2003;Shultz et al., 2005;Le Viol et al., 2012;Sullivan et al., 2016). ...
... We extracted information about habitat specialization of each bird species from Reif et al. (2016). These authors expressed habitat specialization using species specialization index (SSI). ...
... SSI was introduced by Julliard et al. (2006) as a coefficient of variation of species' density across defined set of habitats. Reif et al. (2016) calculated SSI for particular European birds based on the information about their habitat use in Birds of Western Palaearctic Interactive (an electronic version of handbooks of Cramp 1977Cramp -1994, the most comprehensive species-level information source on ecology of European birds) recognizing species presence or absence in 15 habitats: deciduous forest, coniferous forest, woodland, shrub savannah tundra, grassland, mountain meadow, reed, swamps, semi-desert, freshwater, marine, rocks and human settlements (Storchová and Hořák, 2018). Each species has thus a single "pan-European" SSI value. ...
The level of habitat specialization is informative in terms of animals’ population status and conservation concern. Therefore, identifying the areas where specialist species are aggregated and understanding the ecological constrains that might shape their distribution has become an important issue. In this sense, we tested whether specialist communities are more likely to succeed in milder and stable environments or in more extreme and less predictable environments. For that purpose, we used data from the EBCC atlas of European breeding birds and for each of 50 × 50 km grid cells calculated community specialization index (CSI). We expressed CSI in two ways: as a mean (CSIMEAN) and a standard deviation (CSISD) across species in a given cell. We used generalized least squares (GLS) models to relate these measures to geographic variables (latitude, longitude and altitude) and climatic variables (temperature and rainfall) across Europe controlling for possible confounding effects of habitat heterogeneity and human-induced land cover conversion. We identified two areas, Scandinavian Peninsula and the steppe regions north of Caucasus, where bird communities are highly specialised. GLS models showed that habitat specialization generally increased with altitude and this pattern was broadly shared by the CSIMEAN and CSISD. Concerning climatic variables, we found that specialist spatial distribution was significantly related to extreme temperatures and lower level of precipitation. Our results thus suggest that European specialist birds are found mostly in strongly seasonal, dry and cold environments. Thereby, preserving these sensible environments from further perturbations might be the key for the specialist conservation.
... Furthermore, we calculated the species specialization index (SSI; SSI = (H/h − 1) 1/2 for species present in h habitat classes among H possible habitat classes, Julliard et al., 2006) separately for habitat and diet (SSI habitat and SSI diet) following Reif et al. (2016). ...
... In addition, after controlling for suitable habitats, we found that specialists had even higher densities than generalists. This might suggest better adaptations of specialists to their habitats (Pulliam, 1985;Reif et al., 2016) or selection for higher densities, given that specialists have a spatial restriction of preferred environments TA B L E 1 Result for the pgls models relating geographical density (left column) and ecological density (right column) with the body mass, species habitat (SSI habitat), and dietary (SSI diet) specialization. Statistically significant results are provided in bold (Hahn et al., 2011;Hanzelka & Reif, 2015) or population declines are tested Gregory et al., 2007). ...
Species' geographical distributions and abundances are a central focus of current ecological research. Although multiple studies have been conducted on their elucidation, some important information is still missing. One of them is the knowledge of ecological traits of species responsible for the population density variations across geographical (i.e., total physical area) and ecological spaces (i.e., suitable habitat area). This is crucial for understanding how ecological specialization shapes the geographical distribution of species, and provides key knowledge about the sensitivity of species to current environmental challenges. Here, we precisely describe habitat availability for individual species using fine‐scale field data collected across the entire Czech Republic. In the next step, we used this information to test the relationships between bird traits and country‐scale estimates of population densities assessed in both geographical and ecological spaces. We did not find any effect of habitat specialization on avian density in geographical space. But when we recalculated densities for ecological space available, we found a positive correlation with habitat specialization. Specialists occur at higher densities in suitable habitats. Moreover, birds with arboreal and hole‐nesting strategies showed higher densities in both geographical and ecological spaces. However, we found no significant effects of morphological (body mass and structural body size) and reproductive (position along the slow–fast life‐history continuum) traits on avian densities in either geographical or ecological space. Our findings suggest that ecological space availability is a strong determinant of avian abundance and highlight the importance of precise knowledge of species‐specific habitat requirements. Revival of this classical but challenging ecological topic of habitat‐specific densities is needed for both proper understanding of pure ecological issues and practical steps in the conservation of nature. We test the relationships between traits of birds and country scale estimates of population densities assessed in both geographical and ecological space. We did not find any effect of the habitat specialization on avian densities in geographical space, but the effect turned positive once we recalculated the densities for ecological space available. Moreover, birds with arboreal and hole nesting strategies showed higher densities in both geographical and ecological space. However, we found no significant effects of the morphological and reproductive traits on avian densities.
... Migration distance was taken from Hanzelka et al. (2019) who measured the distance between centroids of species' breeding and nonbreeding ranges based on maps taken from BirdLife International and Nature Serve (2014). Climatic niche position was extracted from Reif et al. (2016) as a mean temperature in species' European breeding range in the peak breeding season (April-June). European rarity was quantified as the minus logarithm of the species' relative European breeding population size. ...
... On the other hand, species recorded in forest habitats and various types of human settlements were those more common in Europe. The pattern found for forests is more difficult to interpret, but we suggest that it may be linked to generally lower habitat specialization of European forest birds (Reif et al., 2016) when less specialized species are more common at the same time (Gaston et al., 1997). On the other hand, open habitats showed generally higher rarity values, but interesting differences were observed between different open habitat types. ...
Variation in bird community composition across habitats may be reflected by changes in species’ ecological characteristics. By their comparison between habitats, we can learn information about the factors underlying these changes. With this purpose, we used data from a nation-wide breeding bird monitoring scheme surveying birds in 15 habitat types sorted into four broad categories (forests, open, urban, and humid habitats) in a central European country, Czechia. We considered life-history strategy, migration distance, climatic niche position, European rarity, and diet niche as species’ ecological characteristics and compared their mean values across the habitat types. Although habitat type explained relatively low proportion of variability in these characteristics indicating that birds widely overlap in their habitat use, we observed significant differences in ecological characteristics between broad habitat categories, as well as between habitat types within a given category. For example, urban habitats hosted species with generally lower degree of insectivory than forest habitats. Within forests, coniferous stands hosted species with colder climatic niche than deciduous stands. The greatest differences were observed among humid habitat types: species recorded in water bodies were rarer in Europe and had slower life-history strategies than species recoded in running water. Within the open habitat category, mining areas were the most specific habitat with long-migrating and warm-dwelling species. The observed patterns can be driven by various factors including habitat-specific selection pressures, biogeographic constraints and human-induced habitat changes. On their basis, we discuss our findings.
... Besides the environmental context, a key element to consider when analysing habitat specialisation is represented by behavioural and ecological constraints related to species traits (Irschick et al., 2005). First, diet generalists are expected to exhibit broader habitat niches than diet specialists (Reif et al., 2016). Second, one can expect dispersal to be counter-selected in specialists when movement costs are important (Dahirel et al., 2015) as the spatial grain of resources tends to be coarser for habitat specialists than for generalists, meaning that the average landscape will be perceived as more fragmented by the former (Poisot et al., 2011). ...
... For natural enemies, we found higher connectance and lower modularity in networks of ground beetles compared with spiders. This is consistent with the lower dietary specialisation of ground beetles, that should translate into habitat generalism (Reif et al., 2016). Although landscape configuration (i.e. ...
Measuring habitat specialisation is pivotal for predicting species extinctions and for understanding consequences on ecosystem functioning. Here, we sampled pollinator and natural enemy communities in all major habitat types occurring across multiple agricultural landscapes and used species-habitat networks to determine how habitat specialisation changed along gradients in landscape composition and configuration. Although it is well known that landscape simplification often causes the replacement of specialists with generalists, our study provided evidence for intraspecific variation in habitat specialisation, highlighting how a large number of arthropod species adapted their way of selecting habitat resources depending on the landscape structure. Groups with higher diet specialisation and limited foraging flexibility appeared to have a reduced ability to respond to landscape changes, indicating that some arthropod taxa are better able than others to adapt to an increasingly broad set of resources and persist in highly impacted landscapes.
... These trends suggest that mammal species that share habitat preferences within assemblages tend to have similar diets and parasites but differ in their body mass and activity patterns. Species habitat and diet overlaps have been previously recorded, and may reflect resource availability (Forero et al. 2004, Soininen et al. 2015, Reif et al. 2016, Dehnhard et al. 2019. Similarly, negative correlations between habitat use and activity patterns have been invoked to explain coexistence among sympatric mammals (Namukonde et al. 2018). ...
... Small mammals are more likely to share habitat preferences and diets at more easterly locations such as the Russian Far East and Mongolia. The positive relationship between diet and habitat preferences within mammal assemblages and their uniform geographical patterns may reflect the contingency of diet by habitat choices, as recently reported for European birds (Reif et al. 2016). In this case, the assemblages with the highest functional redundancy for both trait sets include habitat specialist rodents with predominantly herbivorous or granivorous diets while the assemblages with lowest functional redundancy include habitat generalists and a greater array of diets. ...
Functional redundancy (FR) is commonly invoked as one of the main mechanisms underlying ecological resilience. However, little is known about the extension of FR from single to multiple functions and its variation among ecological assemblages at biogeographic scales. We studied 51 assemblages of Eurasian small mammals (Mammalia: Rodentia and Mammalia: Soricomorpha), analyzing FR across and within assemblages. We quantified FR for trait sets related to five different functions: parasitic interactions, diet, habitat preferences, body mass and diel activity. We then evaluated the relationships between FR based on different functional trait sets across and within mammal assemblages, to determine whether small mammal assemblages and their species are redundant for single or multiple trait sets and thus, whether they are complementary or fully redundant when considering multiple functions. Further, we analyzed the influence of geography, climate, plant productivity and land use on FR. We found that FR based on mammal parasitic interactions, body mass and diel activity were positively correlated, whereas FR based on mammal body mass and habitat preferences were negatively related. These relationships were consistent across and within mammal assemblages. Additionally, FR mainly varied along geographic gradients (latitude and longitude). FR based on parasitic interactions, body mass and diel activity followed similar patterns, increasing at northern latitudes, possibly as a response to environmental filtering processes. FR for diet and habitat preferences increased at easterly longitudes, which may be due to landscape homogeneity in sites across central and eastern Asia. Despite redundancy across multiple functional trait sets, Eurasian small mammal assemblages were complementary when considering all five trait sets. Our results warn against conclusions drawn from the study of FR based on traits related to a single function.
... However, it corresponds with generally more positive trends of the rare species reported in other pan-European studies (Inger et al., 2015). Since our models took the negative effect of the habitat specialization, which is typically high in the species with limited geographic distribution (Reif et al., 2016), into account (see above), the pattern is produced by the small range size per se. We suggest that this relationship is a consequence of recent range expansions of the rare species when such species colonize new areas undergoing exponential population growth and thus highly positive trends (Saether & Engen, 2002). ...
... . Data on following eight variables were obtained fromReif, Hořák, Krištín, Kopsová, and Devictor, (2016),Koschova et al. (2018) and Storchova and Horak (2018): (a) position and (b) breadth of species' habitat niche along the gradient from forest interior (value = 1) to open treeless landscape (7); (c) position of species' habitat niche along the habitat gradient from arid (1) to mesic (2) and humid habitats (3); (d) association of species with human settlements (0 = species avoids this habitat, 1 = species occurs in this habitat); (e) diet niche position along the gradient from species feeding obligatory on plants (1) to species feeding obligatory on animals (5); (f) life history strategy (position of species along the slow-fast life history axis obtained by a principal component analysis on six life history traits, namely body mass, egg mass, clutch size, Julian date of first egg laying, number of broods per season and incubation time, discriminating between so-called "K-selected" species with slow strategies and "r-selected" species with fast strategies); (g) position and (h) breadth of species' climatic niche expressed as the mean temperature in their European breeding areas over the peak breeding season (April-June). For following three variables, we used shapefile data on species' breeding and non-breeding ranges provided by BirdLife International and Nature Serve (2018) processed in QGIS 3.6.0 ...
Aim
Population trends reflect influence of environmental drivers acting upon species' population dynamics. As the strength of this influence may change predictably in space, we test multiple hypotheses about spatial gradients in the effects of environmental drivers on bird population trends across the continent.
Location
Europe.
Methods
We used country‐level population trends for 249 bird species in 32 European countries. For each species, we expressed values of 12 traits which mirror the influence of major environmental drivers: climate change, land‐use change and change in environmental legislation. We related these traits to population trends using generalized additive mixed models and tested for the presence of spatial gradients by including the interaction of countries' geographic position with four of these traits for which we hypothesized spatial patterns in relationships to trends.
Results
Species listed for the longest time under Annex I of the EU's Birds Directive had increasingly positive trends towards the north‐west, but an indication of the opposite pattern was found for shorter‐listed species. Cold‐adapted species had increasingly negative trends towards the North and especially the north‐west, whereas the trends of the warm‐adapted species were generally positive and increased in northern direction. Spatial gradients in trends were weaker for the habitat niche position with forest species having positive trends in North‐Eastern Europe and open‐habitat species having negative trends in the Westernmost edge of the continent.
Main conclusions
The influence of all major hypothesized drivers varies across Europe. Climate change impacts are probably most detrimental in North‐Western Europe for the Arctic and upland birds, whereas the warm‐adapted species may benefit from these changes at the same time. The differences in the enforcement of environmental legislation among countries are a likely driver of the spatial patterns for the Annex I species, whereas the unification of land‐use intensity may be the cause of relatively weak patterns in the habitat niche effects.
... The reason might be that many studies focused on only one or a few coarse traits as a measure of ecological specialization (mostly habitat utilization and diet preferences; e.g. Belmaker et al., 2012;Brändle, Prinzing, Pfeifer, & Brandl, 2002;Julliard, Clavel, Devictor, Jiguet, & Couvet, 2006;Reif, Hořák, Krištín, Kopsová, & Devictor, 2015), yet niche partitioning might take place on finer ecological scales, such as foraging behaviour (substrate or methods used for obtaining food). A classic example represents mixed flocks of titmice (family Paridae), where individual species differ in their foraging sites with larger-bodied species foraging on the inner parts of trees while smaller species using mostly outer branches (Jablonski & Lee, 1998;Lack, 1971;Suhonen, Alatalo, & Gustafsson, 1994). ...
... We accounted for range size in the null models where wide-ranging species had a higher probability to be picked than locally occurring ones. Body mass was suggested to be related to specialization (Pineda-Munoz, Evans, & Alroy, 2016), but evidence is missing (Reif et al., 2015). We fit these regressions for all three spatial scales, resulting in six models: specialization and niche overlap (both with and without species' abundances) in localities, and specialization in grid cells and bioregions. ...
Ecological specialization enables the partitioning of resources and thus can facilitate the coexistence of species and promote higher species richness. Specialization and niche partitioning are expected to exert a decisive influence on local spatial scales, while species richness at regional scales should be shaped mostly by historical factors and abiotic conditions. Moreover, specialization is expected to be particularly important in communities that are exceptionally species rich for their environmental conditions. Concurrently, niche overlap in these communities should be minimized to enable species coexistence.
We tested these hypotheses by studying specialization–richness relationship and niche overlap in assemblages of 298 species of songbirds (Passeriformes) across Australia. We used local (2–6 ha) to regional (bioregions) spatial scales and detailed data on habitat, diet and foraging behaviour (method, substrate and stratum).
We expected the richness–specialization relationship to be particularly strong (a) on local spatial scales and (b) in communities exceptionally species rich for given environmental conditions (approximated by moisture and vegetation complexity). We also expected (c) low niche overlap in assemblages with specialized species.
Only the third prediction was partly supported. First, while the specialization and species richness were often positively related, the strength and the direction of the relationship changed between traits and across spatial scales. The strength of the specialization–richness relationship was consistently positive only in foraging stratum, and it increased towards smaller spatial scales only in case of habitat and diet. Simultaneously, species in local communities demonstrated high overlap in habitat and diet. Second, we did not find particularly strong specialization–richness relationships in exceptionally species‐rich communities. Third, we found the expected negative relationship between specialization and overlap in foraging stratum and substrate (in local communities), suggesting that species partition ecological space locally in terms of where they find food.
Our expectations were only weakly supported. Specialization on foraging stratum was probably important in facilitating species coexistence. Conversely, although species were often specialized on habitat and diet, high overlap in these traits did not preclude their local coexistence. Overall, specialization and overlap in foraging traits were more important for species coexistence than habitat or diet.
... It means that many species can occur in different forest types and even though some of the stands hold the characteristics that seem to be preferable for those species, they can also be present in the stands characterized by markedly different values of these characteristics, though less numerous. These results suggest that such species are habitat generalists and correspond to findings of other studies (e.g., Wesolowski et al. 2022) indicating that birds breeding in Northern temperate forests have relatively broad habitat use compared to species associated with other types of environments, such as grasslands (Reif et al. 2016, Barrero et al. 2023. ...
... Its morphology was adapted to live in forest areas (Fjeldså et al. 2005;Goodall et al. 1946;Reid et al. 2002). Reif et al. (2015) determined that birds living in open or sparsely vegetated environments have large wings that allow them increased maneuverability in flight (Harvey & Haber, 1999). On the other hand, the morphology in the forest zone is similar to short-flying birds with short and broad wings, which are related to closed spaces with dense vegetation where they can have quick availability of food; due to the high maneuverability, they have because of their short wings and long tails (Jaroslaw et al. 2014;Revelo Hernández et al. 2016;Viscor & Fuster, 1987). ...
The sub-Antarctic Magellanic ecoregion is one of the most pristine wilderness areas remaining on the planet, and is home to the southernmost forest ecosystems in the world, which are protected by the Cape Horn Biosphere Reserve (CHBR). In these forests, birds are the group of vertebrates with the largest number of species. However, essential aspects of the ecology and morphology of several species in this region are still understudied. These species include the White-throated treerunner (Pygarrhichas albogularis, King 1831), considered a “living fossil” as it is the only living species of the genus Pygarrhichas. In addition, this Furnariid is endemic to the temperate forests of South America. Using the 23-year database of the Long-Term Ornithological Research Program of Omora Park (54º56’S, 67º38’W), based on monthly captures and banding of forest birds, we describe the morphology, longevity, and presence of the White- throated treerunner in the CHBR. Between 2000 and 2022, 91 individuals were captured, including 29 recaptures. Based on these recaptures we determined that this species can live for at least five years. Morphometric measures showed a positive correlation between bill measures and tarsus length with both tail and wing lengths. The average weight varied for each season but not significantly. The greater presence on old-growth forests sites suggests a dependence of treerunners on large trees. This study expands the knowledge about the natural history of the White-throated treerunner, particularly about its populations inhabiting the world’s southernmost forests
... ; https://doi.org/10.1101/2024.04.01.587575 doi: bioRxiv preprint were extracted from 17 . Diet niche position was defined by an ordinal measure ranging from species feeding obligatory on plants (1) to species feeding obligatory on animals (5) 31 . Life history strategy was defined as the position of species along the slow-fast life history axis obtained by a principal component analysis of five life history traits extracted from 32 , namely egg mass, clutch size, age of first breeding, number of broods per season and life span. ...
Dispersal is fundamental to many ecological and evolutionary processes, yet understanding the determinants and predictability of dispersal remains a crucial challenge. Dispersal syndromes, which describe patterns in the covariation of traits associated with dispersal, can help to gain a deeper understanding of the evolutionary dynamics of dispersal and its implications for range dynamics and ecosystem functioning in the face of global change. However, the extent to which such dispersal syndromes are generalizable across a large taxonomic scale has been hampered by low availability of standardized dispersal data across species. In this study, we used the most comprehensive and up-to-date empirical dispersal dataset for European birds to investigate the formation of dispersal syndromes and their effectiveness in predicting dispersal across species. We found body mass, feeding guild, and life-history traits shape dispersal syndromes in birds. Yet, only body mass and life history accurately predicted dispersal for unassessed species, while even multi-trait dispersal syndromes poorly predicted dispersal for phylogenetically distant species. These results shed light on the complex nature of bird dispersal and emphasize the need for refined approaches in elucidating the mechanisms and constraints underlying dispersal evolution. Our study highlights the importance of considering multiple factors and expanding empirical datasets to enhance our understanding of dispersal in avian populations.
... SSI is computed as the coefficient of variation of a species density or occupancy across a given set of habitat types. Values are available for 252 European birds (Reif et al., 2016) based on habitat occupancy across 15 habitat types obtained from Birds of the Western Palaearctic Interactive. STI is computed as the average temperature over the spatial range of a species. ...
... These strategies involve different evolutionary and ecological advantages and constraints (Dennis et al., 2011;Ollerton, 2006), and they have been highly relevant for predicting the loss of interactions and species in gradients of habitat availability (Aizen et al., 2012). In addition, it is known that specialisation in terms of the range of suitable partners is influenced by morphological and reproductive traits (Maglianesi et al., 2014;Otálora et al., 2013;Reif et al., 2016;Santamaría & Rodríguez-Gironés, 2007) and that it is also constrained by species' evolutionary history (Webb et al., 2010). ...
Interactions between organisms are determined by life‐history traits. Ecological strategies regarding species specialisation range from generalist to highly specialised relationships. Although it is expected that habitat fragmentation's effect on species abundance and survival depends on their degree of specialisation and life‐history traits, few studies have delved into the interplay between interaction specialisation, life‐history traits and habitat fragmentation.
Here, we investigate the combined effect of habitat fragmentation, forest structure and life‐history traits (growth form and reproductive mode) on the specialisation of lichen‐forming fungi (mycobionts) toward their photosynthetic partners (photobionts) in lichen symbioses.
We studied mycobiont specialisation in epiphytic lichen communities present in 10 fragments of Quercus rotundifolia forest embedded in an agricultural matrix. Both mycobionts and photobionts were identified DNA barcoding and mycobiont specialisation was measured through interaction parameters calculating the relative number of interactions (normalised degree; ND) and the specialisation of each species based on its discrimination from a random selection of partners (d'). Phylogenetic generalised linear mixed models were used to analyse the effect of patch size as well as the life history traits growth form (crustose, foliose, fruticose) and reproduction mode (sexual vs. asexual) on mycobiont specialisation.
Both mycobiont and photobiont richness along the patch size gradient followed a hump‐back pattern, which was more pronounced in photobionts. Mycobionts forming crustose thalli established the largest number of interactions. Mycobiont specialisation (d') was larger for fruticose and foliose forms and species with vegetative reproduction. Along the gradient of fragment size, the relative number of interactions decreased and the specialisation of mycobionts with vegetative reproduction increased.
Synthesis. The study of mycobiont specialisation towards their photobionts in epiphytic lichen communities in a fragmented Mediterranean forest revealed a complex interaction between species' life history traits and habitat fragmentation. In particular, this interplay had a significant impact on the specialisation of mycobionts. The results show the ability of some species to modulate their specialisation according to habitat conditions, suggesting that some species may be more resilient to abiotic changes than expected.
... According to Morelli et al. (2019), evenness-based measures of specialization provide information on species adaptations to environmental conditions. However, the identification of traits representing the relevant dimensions of environmental space remains challenging (Reif et al., 2016). As emphasized by Devictor et al. (2010), specialization can be seen as a functional syndrome in which several traits covary to affect the species fitness and survival, thus allowing the effective exploitation of particular resources. ...
... Hence, optimizing winter foraging performance, while minimizing both thermoregulation costs and predation risk (Villén-Pérez et al. 2013), requires a flexible behavioral strategy which allows individuals to discover new feeding sites or food types (Sol et al. 2005). Thus, individuals vary in how they behaviorally adapt foraging and food selection strategies Communicated by N. A Dochtermann to the environmental conditions (Veľký et al. 2011;Reif et al. 2016). Based on the habitat-dependent selection hypothesis (Réale et al. 2007), animals develop behavioral characteristics fitted to their rearing environment (Van Oers et al. 2015;Quinn et al. 2016), e.g., mediated through received food types and nutritional content or food quantity. ...
Differences in habitat characteristics experienced during rearing associate with variation in a range of behavioral phenotypes such as exploratory behavior, foraging behavior and food selection. The habitat-dependent selection hypothesis predicts that animals develop behavioral characteristics fitted to their rearing environment. Yet, little is known about how habitat characteristics during rearing shape how animals face winter conditions and adjust their winter foraging behavior. The aim of this study was to explore how fine-scale rearing habitat characteristics associate with exploratory behavior, food selection, and foraging performance during winter. For this, we measured habitat characteristics during the breeding season in territories of wild great tits (Parus major) and tested first-year juvenile birds that fledged from these territories for exploratory and foraging behavior at feeders during winter. We found evidence that faster explorers were raised in territories with lower quality habitat characteristics. In addition, fast exploring fledglings visited the feeders significantly more (total visits). Moreover, the rearing environment, via caterpillar availability and tree species composition, determined diet selection during winter in first-year birds. These results show support for the habitat-dependent selection hypothesis, since exploratory behavior as well as food selection during winter associate with habitat features of the rearing territories during development. This pattern can be caused either by the kinds of natural foods prevalent during rearing at these sites or because of intrinsic individual differences. Further experiments are needed to disentangle these two.
Significance statement
Individuals vary in how they behaviorally adapt foraging and food selection strategies to the environmental conditions. A number of studies have shown that animals develop behavioral characteristics fitted to their rearing environment. However, how habitat characteristics during rearing shape the foraging strategy that animals use to face winter conditions is still unknown. We studied these links in yearling great tits using automated feeders that recorded their visits during winter. Fledglings with a higher exploratory score were born in territories with lower quality habitat characteristics and visited the feeders more. Furthermore, we found an association between caterpillar availability and tree species composition in the rearing territory of juveniles and their subsequent food selection in winter. Our study indicates that certain environmental conditions might favor the development of particular behaviors in birds and that early nutrition could shape food choice later in life.
... Theory predicts that island-colonizing populations undergo ecological release creating a larger total population niche width compared to mainland populations contending with greater interspecific competition (fundamental versus realized niche; Van Valen 1965;Diamond 1970, Bolnick 2008). These island populations may show behavioural and/or morphological adaptations for generalist foraging such as longer bills and legs Hsu et al. 2014;Reif et al. 2016;) that enable exploitation of broader niche widths, though adaptations may be restricted to changes in internal physiology or behavioural traits . Additional predictions are that ecologically released island populations should occupy a wider array of habitats compared to source populations (e.g., , and show greater niche variation among individuals, thus increasing a population's niche width by increasing niche differences between individuals. ...
Knowledge of species habitat requirements, movements, and life cycles is important for understanding their ecology and functions in ecosystems, and is critical for enabling their effective conservation and monitoring, particularly in small-island states where conservation resources are limited. Island biogeography and ecological release theories make broadly supported predictions about the evolution of generalist traits among small-island birds in the Caribbean, and this research examines the influence of small-island conditions on the life cycle adaptations, diets, and distribution of birds and their responses to human land-use such as agriculture to inform conservation research and management. Using mist-netting, I found that 10 common terrestrial bird species on Grenada (3 endemic to the East Caribbean) exhibited similar patterns of low breeding period seasonality, followed by synchronized peaks in moult intensity and uncommonly high rates of moult-breeding overlap during peak rainfall and high arthropod abundance, despite the wide range in size, morphology, and phylogeny of these species. I studied patterns of seasonal diet composition and diet-overlap among species using DNA meta-barcoding of feces, which suggested that moult-breeding overlap may result from restricted time periods over which arthropod availability is sufficient for breeding and moult to occur. Diet analyses also indicated that agricultural habitats provide important year-round food sources. Lastly, repeated point-count surveys indicated increased bird diversity and abundance at high elevations and in closed-canopy habitats during the dry season, while many birds moved to low elevations and open-canopy habitats in the wet season. Much of Grenada consists of a diverse mosaic of closed-canopy secondary forest patches, interspersed among more open agroforests and small-scale cropping and grazed areas. These agroecosystems appear to provide important habitats and foods to birds throughout the year, especially more-open canopy agroforests in the wet season, while intact canopy forests provide important dry season habitat, which may be particularly important for species in lowland coastal fringe areas experiencing more intensive agricultural, urban, and resort development. This research demonstrates life history adaptations of birds on small islands, the importance of maintaining habitat diversity at local and landscape scales for species conservation, and the contribution of diverse small-scale agroecosystems to supporting small-island bird communities.
... Some temporal and spatial avian migration patterns may be inherited and are generally under strong selective pressures (Åkesson & Helm, 2020;Gu et al., 2021;Liedvogel et al., 2011), leading to hypothesize the existence of a phylogenetic signal on the strength of migratory connectivity because selective pressures and migration costs can be shared between closely-related species. Additionally, since avian migration is largely influenced by life-history traits such as niche specialization (Reif et al., 2016;Romano et al., 2023) and body mass-dependent energetic costs of aerial locomotion (Hein et al., 2012), these and other similar ecological factors could play critical roles in determining how birds redistribute between breeding and nonbreeding ranges. ...
Migratory connectivity, reflecting the extent by which migrants tend to maintain their reciprocal positions in seasonal ranges, can assist in the conservation and management of mobile species, yet relevant drivers remain unclear. Taking advantage of an exceptionally large (~150,000 individuals, 83 species) and more‐than‐a‐century‐long dataset of bird ringing encounters, we investigated eco‐evolutionary drivers of migratory connectivity in both short‐ and long‐distance Afro‐Palearctic migratory birds. Connectivity was strongly associated with geographical proxies of migration costs and was weakly influenced by biological traits and phylogeny, suggesting the evolutionary lability of migratory behaviour. The large intraspecific variability in avian migration strategies, through which most species geographically split into distinct migratory populations, explained why most of them were significantly connected. By unravelling key determinants of migratory connectivity, our study improves knowledge about the resilience of avian migrants to ecological perturbations, providing a critical tool to inform transboundary conservation and management strategies at the population level.
... The distributions of ecologically equivalent species will vary stochastically, but with spatial aggregation resulting from dispersal limitations (Freestone and Inouye, 2006). A basic way to detect habitat specialization is by asking if sites where a species is present differ in their environmental conditions from sites where it is absent (Reif et al., 2016). This is particularly relevant for species that occupy a (seemingly) similar ecological niche, such as floating aquatic plants. ...
... According to Morelli et al. (2019), evenness-based measures of specialization provide information on species adaptations to environmental conditions. However, the identification of traits representing the relevant dimensions of environmental space remains challenging (Reif et al., 2016). As emphasized by Devictor et al. (2010), specialization can be seen as a functional syndrome in which several traits covary to affect the species fitness and survival, thus allowing the effective exploitation of particular resources. ...
Specialization refers to a species adaptation to a restricted range of environmental conditions. While generalist species are able to exploit a wide variety of resources in a broad range of habitats, specialist species tend to have narrower niche breadths. From an evolutionary perspective, specialization is the result of a functional syndrome in which a suite of traits covary to allow the effective exploitation of specific resources. Accordingly, the measurement of specialization should be based on a multi-trait approach. In plant ecology, a well-known classification of the adaptive strategies of plants is Grime's competitor, stress tolerator, ruderal (CSR) theory in which the three principal strategies represent relatively easily measurable trait combinations from the global spectrum of plant form and function arising under conditions of competition, abiotic restriction to growth or periodic disturbance, respectively. In this paper, we thus introduce a method to summarize the functional specialization of plant species and communities by applying inequality measures to Grime's CSR strategies. The general idea is that a plant species that can be exclusively assigned to one CSR strategy can be considered a specialist (as it adopts only one adaptive strategy to access resources), while species that share functional characteristics of multiple CSR strategies can be considered more generalist. The behavior of the proposed measures is shown with one case study on the functional changes of six Alpine vegetation types ordered along a gradient, from pioneer to more stable communities.
... The distributions of ecologically equivalent species will vary stochastically, but with spatial aggregation resulting from dispersal limitations (Freestone and Inouye, 2006). A basic way to detect habitat specialization is by asking if sites where a species is present differ in their environmental conditions from sites where it is absent (Reif et al., 2016). This is particularly relevant for species that occupy a (seemingly) similar ecological niche, such as floating aquatic plants. ...
Communities of free-floating aquatic plants dominated by Lemnaceae (duckweeds) are common in ponds and wetlands globally with important ecological functions. In addition to the common duckweed (Lemna minor), other species of Lemnaceae, liverworts (Ricciaceae) and water ferns (Salviniaceae) often coexist over broad geographic areas. Despite these species all sharing a similar mode of life and resource requirements, they have important morphological and physiological differences. The degree to which these differences play a role in shaping their distributions is, however, unclear. We report a field survey of floating aquatic plants in southern Quebec, Canada. We find that species distributions are influenced by habitat specialisation to water phosphorus levels. High nutrient specialisation also followed a continual reduction in body size and morphological complexity, with smaller, simpler species found in higher nutrient sites. We also found a latitudinal gradient in species richness with more northerly sites supporting less diversity. Rare species did not show clustering suggesting that dispersal limitation was not an important factor in determining local abundance. The distribution of these plants appears to be the result of competitive sorting of suitable species from the regional species pool.
Keywords: Lemnaceae, Ricciaceae, species distributions, species richness, diversity gradient, field survey, Macrophytes
... This is relevant because variation in migration and foraging behavior, at the intraspecies level, can place different evolutionary pressures on individual physiology and act as selective forces across populations. That is, a trade-off may exist between longer and more energetically costly migratory routes, potentially resulting in decreased body condition, and alternative strategies involving diet changes or morphological adaptations (e.g., longer or pointed wings) to accommodate the increased energetic demands of their migratory journey (Kaboli et al. 2007, Reif et al. 2016). ...
Whether and how migratory organisms exhibit interindividual behavioral and/or physiological variation across movement strategies remains an open question. The Dark-eyed Junco (Junco hyemalis) is a migratory songbird known for its intraspecies variation displayed in relation to morphology, song repertoires, and migration. Thus, studies focusing on juncos can reveal how migratory strategy may covary with other individual-scale factors and, therefore, identify the selective forces driving intraspecies variations throughout its distribution. We used Dark-eyed Junco hydrogen stable isotope feather values (δ²H) and implemented a Bayesian framework to infer the breeding and molting origin of migratory juncos captured on their winter grounds in Oklahoma, USA. We modeled the distribution of feather hydrogen stable isotope values as a function of five morphological variables including body mass and fat deposition measured in Oklahoma during the winter. We then investigated the trade-off between longer and more energetically costly migration strategies, in relation to diet preferences through carbon (δ13C) and nitrogen (δ15N) stable isotope analysis, from feather values. Dark-eyed Juncos wintering in south central U.S. likely originate from multiple breeding populations in northern U.S. and Canada. Body condition at the wintering ground (e.g., mass) had no effect on feather hydrogen stable isotope abundance. However, we found a positive correlation between nitrogen and hydrogen stable isotopes, suggesting that a trophic level shift toward insect consumption might occur in individuals migrating from southern latitudes. Increased insect-derived protein consumption might be explained by reduced fatty-acid reserves necessary to complete a shorter migratory journey.
... Birds are excellent indicators for environmental conditions and overall biodiversity of a habitat (Reif et al., 2016;Newton 2017, Reif andHanzelka 2020). In general, habitat heterogeneity is known to be an important driver of species richness and abundance of breeding birds (Benton et al. 2003;Farwell et al., 2020;Brüggeshemke et al., 2022). ...
Relative to their biomass or abundance, keystone species have a disproportionate effect on many other organisms. Common juniper (Juniperus communis) is an evergreen shrub that has significant impacts on microclimate, composition of plant assemblages and herbivorous insects. However, J. communis is currently not considered a keystone species. The present study aims to provide deeper insights into the potential importance of juniper as a keystone species in its two main habitats: calcareous grasslands and heathlands. The response of breeding birds to the occurrence of Common juniper was highly similar in both habitat types. Plots with the presence of J. communis had a higher species richness and density of all and shrub-nesting species than absence plots. Additionally, presence plots exhibited a higher density (calcareous grasslands) or richness (heathlands) of threatened species than absence plots. Overall, the occurrence of scattered juniper shrubs boosted species richness and abundance of breeding birds. Responsible for this pattern were (i) the general increase in structural complexity and (ii) two (genuine) properties of the tall, evergreen shrub in particular: dense growth and prickly leaves. Due to the latter, the shrubs provide nesting sites that are strongly sheltered against predation and adverse weather. However, juniper shrubs have also an important function as song posts and perches for hunting. Additionally, the usually scattered distribution of juniper shrubs ensures a maximum territory density in calcareous grasslands and heathlands. Our study provides evidence that J. communis should be considered a keystone species in both habitat types of European conservation concern.
... For example, migratory and resident birds have been shown to differ in traits such as body mass (Hein et al. 2012;Soriano-Redondo et al. 2020) and clutch size (Jetz et al. 2008). Migrants often show stronger habitat (Martin & Fahrig 2018;Zurell et al. 2018; but see Reif et al. 2016), diet (Boyle et al. 2011;Fristoe 2015), and climate (Gómez et al. 2016; but see Dufour et al. 2020) specialization than partial migrants or resident species, who are often generalists that possess a broader spectrum of trait values conferring tolerance to harsh winter conditions of temperate regions. Furthermore, seasonality in resource availability leads to a disproportionate decrease in the occurrence of species that depend on resources typically unavailable during winter (Somveille et al. 2015) such as obligate insectivores (Fristoe 2015). ...
Each year, seasonal bird migration leads to an immense redistribution of species occurrence and abundances, with pervasive, though unclear, consequences for patterns of multi-faceted avian diversity. Here, we uncover stark disparities in spatiotemporal variation between avian taxonomic and functional diversity across the continental US. In the eastern US, the temporal patterns of taxonomic and functional diversity are diametrically opposed, with functional richness highest in winter despite seasonal loss of species, and the remaining most abundant species amassed in a few regions of the functional space that likely reflect the resources available in winter. In contrast, in the western US, both species and functional richness are high during the breeding season, and species’ abundances are regularly distributed and widely spread across the functional space. We anticipate that the uncovered complexity of spatiotemporal associations among avian diversity measures will be the catalyst for adopting an explicitly temporal framework for multi-faceted biodiversity analysis.
... While any discussion on this finding is highly speculative, this result may indicate that threatened mammals are rather conservative in maintaining the same niche volume irrespective of the protection status of the land where they are found. Ultimately, it is often challenging to predict the link between species traits and niche properties 39 , and this study confirms such challenges. For example, few studies have shown that species traits may not represent robust predictors of species responses to environmental change, and that site-and species-specific responses are challenging the identification of broad patterns at the large scale 40,41 . ...
Protected areas are a cornerstone for biodiversity conservation, and typically support more natural and undisturbed habitats compared to unprotected lands. The effect of protected areas on intra-specific ecological niche has been rarely investigated. Here, we explore potential differences in ecological niche properties of birds and mammals across protected and unprotected areas, and relate such differences to species traits. We combine two decades of survey data of birds and mammals from protected and unprotected areas, and apply robust matching to obtain a set of environmentally comparable protected and unprotected sites. Next, we calculate intra-specific niche volume change and habitat shift between protected and unprotected areas, and use generalized linear mixed models to explain these responses with species traits (habitat specialization, body mass, diet, and red list status). The majority of bird and mammal species (83% and 90%, respectively) show different habitat use when occurring within and outside protected areas, with the magnitude of this shift highly varying across species. A minority of species (16% of birds and 10% of mammals) do not change their niche volume nor shift their habitat between protected and unprotected areas. Variation in niche properties is largely unrelated to species traits. Overall, the varying ecological niche responses of birds and mammals to protected areas underscore that there is no universal niche-based response, and that niche responses to land protection are species-specific.
... The negative impact of patches' number on the abundance of ground/herb dwellers, gradually enhanced by the increasing plant invasion area (and especially rapid near the largest invasion areas), seems intuitive. It is known that the abundance of narrow-ranging species, consisting mainly of habitat specialists (Reif et al., 2016), is highest in the homogeneous landscapes, and the majority of narrow-ranging species are open-landscape specialists (Katayama et al., 2014), i.e. ground/herb dwellers in our case. ...
The availability of various habitats increases biodiversity and provides niche opportunities for organisms, although greater habitat diversity may contribute to the spreading of invasive plants. In this study, we aimed to assess the impact of the extent of invasion on bird responses to the availability of their natural habitats. Specifically, we asked whether the Caucasian hogweeds, herbaceous invasive plants spreading in abandoned lands, shape those responses by providing new niche opportunities or limitations and whether these invaders can be tolerated by the bird community. The research was conducted in south-eastern Poland in 2020 on 64 research sites, half of which were located near the Caucasian hogweeds’ invasion. The birds were counted from points within 100 m, while the areas of invaded and uninvaded habitats were measured within 100 and 500 m. The impact of the invaded area was negative for the overall bird abundance and species richness. At the same time, the invasion affected birds differently depending on their nesting/foraging assemblages, the availability of various uninvaded habitats, and the extent of invaded areas. Specifically, the abundance of ground/herb dwellers non-linearly dropped even with small increases of the invaded area suggesting their high sensitivity to invasion. These birds were supported by the agricultural land availability, but only when its area was lower than 1.0 ha and the habitat was fragmented, indicating the value of extensive croplands for ground/herb dwelling species. Ecotone birds benefited from small invaded areas mixed with bushes but suffered when the invaded areas were large. Habitat homogenization by the invader physiognomically similar to shrubs was favoured by bush foragers. Tree foragers preferred forest partitioning near the largest invaded areas. The invaded and uninvaded habitats influenced bird community at a fine scale (i.e. in a 100-m radius), while only crucial areas of meadows, forests and agriculture available in a 500-m radius remained important for the community. This study showed that even a small amount of plant invaders rapidly and negatively affect birds when they grow in open areas and are physiognomically different from these birds’ habitats, while species living in ecotone or trees suffer from severely invaded areas. It suggests the priority of invading weeds’ removal in open areas, regardless of the invaded area, as well as the need to prevent weed development in overgrown areas.
... As species' traits, I focused on body mass and habitat preference (open habitat and tree/shrub habitat). These traits are frequently used in understanding functional or phylogenetic structure of birds due to their strong association with many other traits (Reif et al., 2016; see Supporting Information Table S2 for the list of species and their traits). I did not include diet or foraging stratum because 80% of open habitat species are insectivores or ground foragers with no frugivores/nectivores or canopy foragers, showing not only little variation in these two traits but also high correlation between them and habitat preference. ...
Greenspace or green cover is one of the major factors affecting urban avian diversity. In China, small farmlands producing vegetables are relatively common in cities. Although these farmlands could be a part of greenspaces, their habitat value for birds is rarely known. I investigated how these farmlands influenced winter bird community in two cities of southern China, using the multivariate latent variable model. I considered three green cover types: crop (mostly vegetables), weed (pioneer spontaneous vegetation), and wood (tree/shrub). I calculated the percentage of each green cover at local (50 m radius circular area) and landscape (500 m radius circular area) scales. Of 30 bird species, the abundance of 13 species decreased as crop cover decreased with increasing woody cover at the local scale, whereas the abundance of only two bird species increased with decreasing crop cover. Habitat preference of species mediated these responses, leading to a strong association between the open habit trait and the negative responses. Open habitat bird species richness was also negatively affected by decreasing local crop cover. Tree/shrub bird species richness showed a positive response to decreasing crop cover but the explanatory power of the local scale model was low. Variables at the landscape scale were rarely associated with species abundance or richness. These results suggest that small vegetable‐dominant farmlands can serve as open habitat for birds in urban areas where greenspace largely consists of tree/shrub vegetation. The results also indicate that urban bird diversity is more influenced by local habitat features than landscape‐scale features.
... Moreover, at middle elevations, overdispersion among traits provided some evidence of niche partitioning among the most species-rich communities (See Figure 2b). We suggest that community assembly in high-altitude river birds must therefore reflect a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche-based selection of trait character for specialization (Morelli et al., 2019;Reif et al., 2016). This effect is particularly well illustrated in the forktails (Enicurus spp.), in which tail length in the Little Forktail is substantially reduced in comparison to its congeners and potentially linked to its highly specialized foraging niche around the splash zone of large boulders in highly turbulent flows (Buckton & Ormerod, 2008 ...
Abstract Heterogeneity in riverine habitats acts as a template for species evolution that influences river communities at different spatio‐temporal scales. Although birds are conspicuous elements of these communities, the roles of phylogeny, functional traits, and habitat character in their niche use or species' assembly have seldom been investigated. We explored these themes by surveying multiple headwaters over 3000 m of elevation in the Himalayan Mountains of India where the specialist birds of montane rivers reach their greatest diversity on Earth. After ordinating community composition, species traits, and habitat character, we investigated whether river bird traits varied with elevation in ways that were constrained or independent of phylogeny, hypothesizing that trait patterns reflect environmental filtering. Community composition and trait representation varied strongly with increasing elevation and river naturalness as species that foraged in the river/riparian ecotone gave way to small insectivores with direct trophic dependence on the river or its immediate channel. These trends were influenced strongly by phylogeny as communities became more clustered by functional traits at a higher elevation. Phylogenetic signals varied among traits, however, and were reflected in body mass, bill size, and tarsus length more than in body size, tail length, and breeding strategy. These variations imply that community assembly in high‐altitude river birds reflects a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche‐based moulding of trait character. We suggest that the regional co‐existence of river birds in the Himalaya is facilitated by this same array of factors that together reflect the highly heterogeneous template of river habitats provided by these mountain headwaters.
... The bird abundance for each species was indexed by the maximum number of individuals of that species detected by the observer in any of the four surveys. We classified the bird species as habitat specialists or generalists according to Julliard et al. (2006), Reif et al. (2010Reif et al. ( , 2016, Le Viol et al. (2012), and Morelli et al. (2019). We classified the top 35% of bird species by SSI as specialists (see Table 1A for more details). ...
Vineyards are semi-natural, human-modified ecosystems where the extent of natural elements is determined primarily by the type of management and by the abandonment rate. In this study, we analyzed bird assemblages in 40 vineyard plots in six wine-growing regions of Slovakia. We examined bird communities on managed and abandoned vineyards to identify possible patterns. Environmental and spatial predictors of species richness and abundance were analyzed using partial redundancy analysis (pRDA) and a generalized additive model (GAM). Bird communities were influenced by both environmental and spatial factors. As expected, elevation explained most of the variation in bird assemblages. Tree coverage was found to be more important than the vineyard abandonment rate in explaining the observed variability. Only a portion of the variance in the species data reported by pRDA was accounted for by the difference in vineyard abandonment degree. Our results show that the species richness of all birds was positively correlated to vegetation density (captured by NDVI). Herb and shrub cover had less effect on bird species richness than tree cover and the presence of traditional agricultural vineyard landscapes. However, shrub density emerged as a key explanatory factor for the abundance of habitat specialists. Our study shows that, depending on whether the goal is to promote the diversity and abundance of farmland or non-farmland bird species, different conservation biology approaches should be used. Increasing the landscape diversity and avoiding large vineyard abandonment are necessary if we are to stem the decline of valuable farmland species.
Keywords
... Migration behaviour can also affect habitat use by animals, for example, migratory mule deer have access to higher quality habitat than non-migratory individuals (Nicholson et al., 1997). Whereas in birds, habitat specialists are seen to migrate shorter distance than habitat generalists (Reif et al., 2016). However, our current understanding of how species-specific traits can help predict shifts of animals to other habitats remains limited (MacLean & Beissinger, 2017). ...
Aim:
Abundances of animals vary according to species-specific habitat selection, but habitats are undergoing rapid change in response to anthropogenic alterations of land use and climate. The long-term decline of snowfall is one of the most dramatic abiotic changes in boreal regions, with potential to alter species communities and shape future ecosystems. However, the effects of snow cover on habitat-specific abundances remain unclear for many taxa. Here we explore whether long-term declines in snow cover affect the abundances of overwintering birds.
Taxon:
Fifty bird species.
Location:
Finland, Northern Europe.
Methods:
We used generalized linear mixed models to analyse citizen-led monitoring data from 196 transects over a 32-year period to assess whether abundances of birds have changed in built-up areas, farmlands and forests, and whether these covary with warming temperatures and decreasing snow. We then explored if changes in abundance can be explained by body mass, migration strategy or feeding guilds of the species.
Results:
Over the study period, the abundance of overwintering birds increased. This increase was most pronounced in farmlands (69.6%), where abundances were positively associated with decreasing snow depth. On the other hand, while abundances in built-up habitats (19.5%) decreased over the study period, they increased in periods of high snow depths. Finally, we found that the short-distance migration strategy explains changes in bird abundances with snow. In farmlands, ground feeding birds and heavier birds also show a positive trends in abundance with decreasing snow depths.
Main conclusions:
Local snow conditions are driving habitat selection of birds in the winter; birds in farmlands were most responsive to a decrease in snow depth. Changing snow depths can affect bird movements across habitats in the winter, but also influence migratory patterns and range shifts of species.
... Moreover, at middle elevations, overdispersion among traits provided some evidence of niche partitioning among the most species-rich communities (See Figure 2b). We suggest that community assembly in high-altitude river birds must therefore reflect a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche-based selection of trait character for specialization (Morelli et al., 2019;Reif et al., 2016). This effect is particularly well illustrated in the forktails (Enicurus spp.), in which tail length in the Little Forktail is substantially reduced in comparison to its congeners and potentially linked to its highly specialized foraging niche around the splash zone of large boulders in highly turbulent flows (Buckton & Ormerod, 2008 ...
Heterogeneity in riverine habitats acts as a template for species evolution that influences river communities at different spatio-temporal scales. Although birds are conspicuous elements of these communities, the roles of phylogeny, functional traits and habitat character in their niche-use or species’ assembly have seldom been investigated. We explored these themes by surveying multiple headwaters over 3000 m of elevation in the Himalayan Mountains of India where specialist river birds reach their greatest diversity on Earth. After ordinating community composition, species traits and habitat character, we investigated whether river-bird traits varied with elevation in ways that were constrained or independent of phylogeny, hypothesising that trait patterns reflect environmental filtering. Community composition and trait representation varied strongly with elevation and river naturalness as species that foraged in the river/riparian ecotone gave way to small insectivores with obligate links to the river channel. These trends were influenced strongly by phylogeny as communities became more clustered by functional traits at higher elevation. Phylogenetic signals varied among traits, however, and were reflected in body mass, bill size and tarsus length more than in body size, tail length and breeding strategy. These variations imply that community assembly in high altitude river birds reflects a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche-based moulding of trait character. We suggest that the regional co-existence of river birds in the Himalaya is facilitated by the same array of factors that together reflect the highly heterogeneous template of river habitats provided by these mountain headwaters.
... This 61 is relevant because variation in migration and foraging behavior at the intra-species level can 62 place different evolutionary pressures on individual physiology and act as selective forces across 63 populations. That is, there might be a trade-off between longer and more energetically costly 64 migratory routes, potentially resulting in decreased body condition, and alternative strategies 65 involving diet changes or morphological adaptations (e.g., longer or pointed wings) to 66 accommodate the increased energetic demands of their migratory journey (Kaboli et al, 2007; 67 Reif et al., 2016). 68 outcome would be especially likely if individuals migrate directly from northern latitudes 96 without utilizing stopover sites, such that they bear the costs of migration all at once (Cooper et 97 al., 2015). ...
Whether and how migratory organisms exhibit inter-individual behavioral and/or physiological variation across movement strategies remains an open question. The Dark-eyed Junco (Junco hyemalis) is a migratory songbird known for its intra-species variation displayed in relation to morphology, song repertoires, and migration. Thus, studies focusing on juncos can reveal how migratory strategy may covary with other individual-scale factors and, therefore, identify the selective forces driving intra-species variations throughout its distribution. We used Dark-eyed Junco hydrogen stable isotope feather values (delta2H) and implemented a Bayesian framework to infer the breeding and molting origin of migratory juncos captured on their winter grounds in Oklahoma, United States (U.S.). We modeled the distribution of feather hydrogen stable isotope values as a function of five morphological variables including body mass and fat deposition measured in Oklahoma during the winter. We then investigated the trade-off between longer and more energetically costly migration strategies in relation to diet preferences through carbon (delta13C) and nitrogen (delta15N) stable isotope analysis from feather values. Dark-eyed Juncos wintering in south central U.S. likely originate from multiple breeding populations in northern U.S. and Canada. Body condition at the wintering ground (e.g., mass) had no effect on feather hydrogen stable isotope abundance. However, we found a positive correlation between nitrogen and hydrogen stable isotopes, suggesting that a trophic level shift towards insect consumption might occur in individuals migrating from southern latitudes. Increased insect-derived protein consumption might be explained by reduced fatty-acid reserves necessary to complete a shorter migratory journey.
... While the classification of species into functional groups has a long tradition (Raunkiaer, 1934;Weiher et al., 1999), the definition of a "trait" has shifted from a simple grouping towards a more quantitative categorisation, allowing more predictive science within ecology (McGill et al., 2006). Trait-based approaches are now abundantly used to answer research questions across a variety of topics including community ecology (Mouillot et al., 2013;Satdichanh et al., 2015), species diversity gradients (Lamanna et al., 2014;Whittaker et al., 2014;Si et al., 2017;Costa et al., 2018b), responses to environmental change (Bjorkman et al., 2018;Liu et al., 2018;Winchell et al., 2020), and niche dynamics (Reif et al., 2016;Costa et al., 2018b). ...
Aim: Trait-based approaches are increasingly important in ecology and biogeography, but progress is often hampered by the availability of high-quality quantitative trait data collected in the field. Alternative sources of trait information include scientific floras and taxonomic monographs. Here we test the reliability and usefulness of trait
data acquired from scientific floras against trait values measured in the field, and those in TRY, the most comprehensive global plant trait database.
Location: Tenerife and La Palma, Canary Islands, Spain.
Methods: We measured leaf area and specific leaf area (SLA) in the field for 451 native vascular plant species and compared them with equivalent trait data digitised from the most recent and comprehensive guide of the Canarian flora, and data sourced from TRY. We regressed the field-measured traits against their equivalents estimated from the literature and used the regression models from one island to predict the trait values on the other island.
Results: For leaf area, linear models showed good agreement between values from the scientific flora and those measured in the field (r2 = 0.86). These models were spatially transferable across islands. In contrast, for SLA we found a weak relationship between field-measured values and the best estimates from the scientific flora
(r2 = 0.11). Insufficient data were available in the TRY database for our study area to calculate trait correlations with other data sources.
Conclusions: Scientific floras can act as useful data sources for quantitative plant trait data for some traits but not others, whilst the TRY database contains many traits, but is incomplete in species coverage for our study region, and oceanic islands in general.
... However, morphological traits could serve multiple functions and influence various niche dimensions, and vice versa, weakening the covariance among morphological traits, ecological functions, and niche dimensions (e.g., Felice et al., 2019;Kennedy et al., 2020;Navalón et al., 2019). Such "many-to-one" or "one-to-many" relationships between morphological traits and ecological functions both create challenges and offer opportunities for trait-based and niche-based predictions (Kennedy et al., 2020;Reif et al., 2016;Wainwright et al., 2005;Webb et al., 2010). ...
The niche variation hypothesis (NVH) predicts that populations with wider niches exhibit greater morphological variation through increased interindividual differences in both niche and morphology. In this study, we examined niche–trait relationships in three passerine species (Cyanoderma ruficeps, Sinosuthora webbiana, and Zosterops simplex). A total of 289 C. ruficeps from 7 sites, 259 S. webbiana from 8 sites, and 144 Z. simplex from 6 sites were sampled along an elevation gradient (0–2,700 m) in Taiwan from 2009 to 2017. We measured bill traits (length, width, and depth of bill) and body size traits (length of head, tarsus, and wing) of the birds, which were reduced to four principal components (bill PC1, bill PC2, body size PC1, and body size PC2). We collected feather tissues for stable carbon and nitrogen isotope analyses to quantify their isotope niche. We quantified interindividual differences in isotope space and trait space with four diversity metrics (divergence, dispersion, evenness, and uniqueness) and tested whether interindividual differences in isotope space and trait space are positively associated. We quantified population isotope niche width by Bayesian ellipse area and population morphological variation by variances of the PCs. The results showed that individual uniqueness in isotope niche and bill morphology (average closeness of individuals within the population isotope/trait space) were positively associated across three species. Furthermore, isotope niche width and bill PC1 (reflecting the size of bill) variation at population level were also positively associated across the three species, supporting the NVH. Of the three species, C. ruficeps and S. webbiana showed stronger support for the NVH than Z. simplex, possibly due to the latter having narrower elevational distribution and a more specialized, plant‐based diet. The diversity metrics represented different aspects of interindividual differences in niche/trait space, and for the passerines, individual uniqueness appeared to play an important role in their niche–trait dynamics. This study provided empirical evidence for the niche variation hypothesis in three passerine species (Cyanoderma ruficeps, Sinosuthora webbiana, and Zosterops simplex) in Taiwan. All three species showed positive associations between isotope niche width and bill size variation. Furthermore, all three species shared the same pattern that as individual birds occupied unique bill trait space within the population, they also tended to occupy unique isotope space, suggesting niche width expansion at population level through morphological differentiation at individual level.
... On the other hand, however, many species including birds are specialists and/or poor competitors, preferring specific habitats with relatively lower habitat heterogeneity or low primary productivity (Reif, Hořák, Krištín, Kopsová, & Devictor, 2016). The occurrence of these species can be associated with early stages of spontaneous succession, which are rare in the cultural landscape but relatively common on restored sites (Šálek, 2012). ...
Management of restored areas requires ecologically meaningful spatial data providing objective measures of restoration success. Understanding relationships between species diversity on the one hand and habitat heterogeneity and productivity on the other can help establish such measures and prioritize restoration management. We used airborne LiDAR and hyperspectral data to derive characteristics of vegetation structure, primary productivity and senescent vegetation (i.e. old dead vegetation) for prediction of richness and rarity of bird communities colonizing newly available habitats restored after coal mining. In addition, we analysed, which type of restoration (i.e. agricultural, forest, or spontaneous succession) results in more favourable conditions. The boosted regression trees explained 52% and 12% of deviance of overall species richness and rarity, respectively. We found that the overall species richness was strongly affected by the variance in vegetation structure, while the rarity was also affected by the presence of senescent vegetation. The relative importance of variables differed between the richness and rarity. The shrub cover had a strong positive effect on both, while the tree cover had a strong positive effect on species richness. The herbaceous cover and presence of senescent vegetation had positive effects on species rarity. This study, therefore, supports the necessity to create a mosaic of habitats with heterogeneous vertical structure including all layers of vegetation and highlights the importance of senescent vegetation. Combination of forests restoration with sites left to spontaneous succession appears to be the best strategy to increase both bird species richness and rarity in newly restored sites after coal mining.
... In cases when range boundaries are proximately determined by climatic niche (Fig. 1c-d) and the species has nowhere to expand without broadening its niche, traits such as migratory behavior may be less likely to influence range expansion. The relationship between species' migratory behavior and the breadth of their climatic niches has been a topic of increasing interest in recent years (Gómez et al. 2016, Reif et al. 2016, Martin and Fahrig 2018, Ponti et al. 2019) and results of further such studies will contribute to our understanding of the biogeography of migratory taxa. ...
Seasonal migration has been alternately proposed to promote geographic range size in some contexts and to constrain it in others, but it remains unclear if migratory behavior has a general effect on range size. Because migration involves movement, most hypotheses about the relationship between migration and range size invoke an influence of migration on the process of dispersal‐mediated range expansion. Intuitively, a positive relationship between migratory behavior and dispersal ability could bolster range expansion among migratory species, yet some biogeographic patterns suggest that long‐distance migration may instead impede range expansion, especially in the temperate zone. We conducted a comparative analysis of the relationship between migratory behavior and range size by testing the effect of migratory status, migration distance and morphological dispersal ability on breeding range size among all temperate North American passerines. Further, we assessed whether these traits affect range expansion into suitable habitat by analyzing their relationship with range filling (the proportion of climatically‐suitable area occupied, or ‘filled’ by a species). Contrary to previous studies, we found migration and dispersal ability to be poor predictors of range size and range filling in North America. Rather, most variation in range size is explained by latitude. Our results suggest that migratory behavior does not affect range size within the scale of a continent, and furthermore, that temperate North American passerines’ breeding ranges are not influenced by their dispersal abilities. To better understand why migratory behavior appears to promote range size in some contexts and constrain it in others, future studies should investigate how migratory behavior affects dispersal at the individual level, as well as the relationship between the evolution of migratory behavior and the breadth of species’ climatic niches.
... The partially tubular tongue structure (Fig. 3), the presence of arthropod material in the stomach, and observations of the species foraging on Medinella (Melastomataceae) berries suggest a diet similar to that of other flowerpeckers in which a mistletoe-dominated diet is supplemented to some extent by nectarivory, general frugivory, and arthropod predation. The role of diet specialization on habitat preference and distribution is poorly known (Reif et al. 2016). The various species of mistletoe that the bird has been observed to consume are ubiquitous species of Southeast Asia that likely occur widely throughout Borneo where mature forests persist (Beaman et al. 2001(Beaman et al. , 2004. ...
The enigmatic ‘Spectacled Flowerpecker’—a probable new bird species from the island of Borneo—was first sighted in the Danum Valley of Sabah, Malaysia in 2009. However, the absence of a holotype specimen has prevented its formal scientific description. Since then only a handful of reports from widely disparate localities across the island have emerged, all from lowland sites and often in close association with fruiting mistletoe. Here, we report the long-awaited capture of a specimen of this putative new species and confirm its morphological and molecular distinctiveness as a novel species in the genus Dicaeum.
... This pattern may not hold over different taxonomic scales or different niche axes. For example, positive correlations between habitat and diet specialization have been reported in European birds (Reif et al. 2016), but not among birds breeding in Germany or in a broad taxonomic group of coral reef fish (Brändle et al. 2002, Brandl et al. 2015. ...
The concept of the ecological niche is fundamental to understanding constraints on species distributions in space and time, and in explaining the origin and maintenance of biodiversity. A niche can be broadly defined to include all of the biotic and abiotic conditions that a species requires to persist. Niche breadth, or the degree of specialization, may influence how labile a species niche is, which can have broad implications for species ability to adapt to environmental change, and for explaining patterns of diversification. I investigated mechanism that facilitate or constrain niche evolution at multiple scales. First, I developed an index of specialization in bill morphology using museum specimens across a diverse New World Passerine clade. I used this index of specialization to evaluate the relative influence of geographic and ecological niche partitioning on speciation rates across islands and continents. I then examined evolutionary transition rates among generalist and specialist bill morphotypes to determine if specialization constrains further evolution over long time scales, thus creating an evolutionary dead end. My results suggest that specialization increases speciation rates, and that niche expansion allowing transitions from specialist back to a more generalist bill morphology were common. I further explored mechanisms that drive these broad scale patters by examining patterns of intraspecific niche partitioning in closely related tidal marsh passerines. I found that habitat characteristics that reflected a salinity gradient best explained parallel patterns of bill size divergence among populations of two closely related sparrow species. Lastly, I examined if the definition of specialization varies across niche axes. We found that niche breadth, or the degree of specialization, is correlated among functional, environmental, and competition axes among five species of Passerelid sparrows. By examining the influence of specialization on macroevolutionary patterns of diversification and patterns of niche partitioning within species we gain a more comprehensive understanding of how niches evolve across different temporal and taxonomic scales. I found specialization is associated with increased speciation rates that influence continental-scale patterns of diversification. I also provide evidence that specialists retain the potential for niche expansion at the species and population scale. Patterns of intraspecific niche partitioning along habitat gradient presented here also increase our understanding of how species might adapt to change at scales that are applicable to local conservation. My results suggest strategies to incorporate a diversity of habitat characteristics may be beneficial for conserving intraspecific variation and adaptive capacity of specialist species.
... The habitat specificity or species-habitat specialization has been quantified by measuring the breadth of use of a particular habitat type by an individual and hence by implication for a given species (Devictor et al., 2010). Additionally, methods are becoming available to construct continuous measures of habitat generalism-specialism, known as the Species Specialization Index (SSI; Julliard et al., 2006), an approach now applied in many studies (Devictor et al., 2008;Reif, Hořák, Krištín, Kopsová, & Devictor, 2016;Reif, Jiguet, & Šťastný, 2010). The SSI is relatively easy to calculate, because it is based only on the frequency of occurrence of each species in each habitat or land use type available in the study area (Devictor et al., 2008). ...
Measuring the extent to which a species is specialized is a major challenge in ecology, with important repercussions for fundamental research as well as for applied ecol‐ogy and conservation. Here, we develop a multidimensional index of specialization based on five sets of ecological characteristics of breeding bird species. We used two recent databases of species traits of European birds based on foraging ecology, habitat, and breeding characteristics. The indices of specialization were calculated by applying the Gini coefficient, an index of inequality. The Gini coefficient is a measure of statistical dispersion on a scale between 0 and 1, reflecting a gradient from low to high specialization, respectively. Finally, we tested the strength of the phylogenetic signal of each specialization index to understand how the variance of such indices is shared throughout the phylogeny. The methods for constructing and evaluating a multidimensional index of bird specialization could also be applied to other taxa and regions, offering a simple but useful tool, particularly suited for global or biogeo‐graphic studies, as a contribution to comparative estimates of the degree of speciali‐zation of species.
... We applied an a priori approach (Wiens, 1989a) to classify European and North American birds into foraging guilds. We used number of published papers and monographs with descriptions of feeding tactics, diet niches, and use of foraging substrates (e.g., Reif, Hořák, Krištín, Kopsová, & Devictor, 2016). We based detailed classification of individual bird species on the dominant feeding strategy during the breeding period, and it is given in the Appendix S2. ...
Abstract Patterns of species associations have been commonly used to infer interactions among species. If species positively co‐occur, they may form predominantly neutral assemblages, and such patterns suggest a relatively weak role for compensatory dynamics. The main objective of this study was to test this prediction on temporal samples of bird assemblages (n = 19, 10–57 years) by the presence/absence and quantitative null models on assemblage and guild levels. These null model outcomes were further analyzed to evaluate the effects of various data set characteristics on the outcomes of the null models. The analysis of two binary null models in combination with three association indices revealed 20% with significant aggregations, 61% with random associations, and only 19% with significant segregations (n = 95 simulations). The results of the quantitative null model simulations detected more none‐random associations: 61% aggregations, 6% random associations, and 33% segregations (n = 114 simulations). Similarly, quantitative analyses on guild levels showed 58% aggregations, 20% segregations, and 22% random associations (n = 450 simulations). Bayesian GLMs detected that the outcomes of the binary and quantitative null models applied to the assemblage analyses were significantly related to census plot size, whereas the outcomes of the quantitative analyses were also related to the mean population densities of species in the data matrices. In guild‐level analyses, only 9% of the GLMs showed a significant influence of matrix properties (plot size, matrix size, species richness, and mean species population densities) on the null model outcomes. The results did not show the prevalence of negative associations that would have supported compensatory dynamics. Instead, we assume that a similar response of the majority of species to climate‐driven and stochastic factors may be responsible for the revealed predominance of positive associations.
Intraspecific genetic variation and phylogeographic structure can be influenced by factors such as landscape features, environmental gradients, historical biogeography, and organismal traits such as dispersal ability. Since deep genetic structure is often considered a precursor to speciation, identifying the factors that are associated with genetic structure can contribute to a greater understanding about diversification. Here, we use repurposed data to perform a global analysis of volant vertebrates (i.e., bats and birds) to estimate where intraspecific phylogeographic breaks occur and identify the factors that are important predictors of these breaks. We estimate phylogeographic breaks using Monmonier's maximum difference barrier algorithm and conduct a Random Forests analysis using the presence of a phylogeographic break as a response variable. In bats, phylogeographic breaks are concentrated in biodiversity hotspots while breaks estimated in bird species are more widespread across temperate and tropical zones. However, for both clades geographical features such as maximum latitude, measures of wing morphology, and organismal traits associated with feeding ecology were found to be important predictors of phylogeographic breaks. Our analysis identifies geographical areas as wells as suites of organismal traits that could serve as a starting point for more detailed studies of biodiversity processes.
Each year, seasonal bird migration leads to an immense redistribution of species occurrence and abundances,1,2,3 with pervasive, though unclear, consequences for patterns of multi-faceted avian diversity. Here, we uncover stark disparities in spatiotemporal variation between avian taxonomic diversity (TD) and functional diversity (FD) across the continental US. We show that the seasonality of species richness expectedly3 follows a latitudinal gradient, whereas seasonality of FD instead manifests a distinct east-west gradient. In the eastern US, the temporal patterns of TD and FD are diametrically opposed. In winter, functional richness is highest despite seasonal species loss, and the remaining most abundant species are amassed in fewer regions of the functional space relative to the rest of the year, likely reflecting decreased resource availability. In contrast, temporal signatures for TD and FD are more congruent in the western US. There, both species and functional richness peak during the breeding season, and species' abundances are more regularly distributed and widely spread across the functional space than during winter. Our results suggest that migratory birds in the western US disproportionately contribute to avian FD by possessing more unique trait characteristics than resident birds,4,5 while the primary contribution of migrants in the eastern US is through increasing the regularity of abundances within the functional space relative to the rest of the year. We anticipate that the uncovered complexity of spatiotemporal associations among measures of avian diversity will be the catalyst for adopting an explicitly temporal framework for multi-faceted biodiversity analysis.
Underlying biological processes can often shape phenotypic variation. Although subtle, the variation in plumage colour of the Azure Jay (Cyanocorax caeruleus) has long been suggested to be of phylogeographic importance, but this hypothesis was not tested. This species’ distribution in the Atlantic Forest biome of south-eastern Brazil is divided into two ecologically distinct portions by the Serra do Mar mountain line. The availability of Parana Pine (Araucaria angustifolia) seeds is essential for the survival of Azure Jays in the western range but not in the eastern range. Here we quantify Azure Jay geographic variation using three datasets, including vocalisations, morphology and plumage colour. All available data independently supported the hypothesis of divergence between east and west. Azure Jays in the western range tend to have: (1) larger body dimensions, (2) vocalisations with lower pitch and entropy, and (3) a greenish-blue plumage, than those in the eastern range. Based on the available data on this species’ ecology, life history and sociality, we discuss how features from the western range could indicate specialisation in habitat use. We discuss potential links between our results and the past of the Atlantic Forest and the implications for this species conservation in a highly threatened habitat. Finally, we highlight the pressing need for demographic and molecular evidence to make data-oriented and effective decisions for this species conservation.
Farmland biodiversity has undergone drastic declines due to agricultural intensification during the last decades. To prevent further biodiversity loss, the maintenance and restoration of non-productive habitats is essential. Woodlots, small patches of woody vegetation in agricultural landscapes, are one such habitat that are currently subsidized by the European Union’s Common Agricultural Policy (EU’s CAP). For effective implementation, however, it is necessary to assess what habitat characteristics are the most beneficial for biodiversity. Our study performs such an assessment using birds as model organisms. Specifically, we related characteristics of various woodlots to (I) the species richness of all birds, and (II) the species richness of both forest and farmland birds–groups with different ecological requirements. For this purpose, we counted birds (27 farmland and 26 forest species) and measured habitat characteristics (describing vegetation structure, diversity and nativeness) and spatial characteristics (area, shape and isolation) in 82 mid-field woodlots (0.76–1.25 ha, average 0.46 ha) in the Czech Republic (Central Europe). After accounting for the effects of spatial characteristics, overall bird species richness increased with vegetation height and woody plant species richness. In addition, richness showed a non-linear decrease with the cover of an invasive tree, the Black Locust Robinia pseudoaccacia. Interestingly, forest bird species richness was related to the same habitat characteristics as the overall bird species richness. By contrast, farmland bird species richness was positively related to the diversity of woodlot microhabitats, which reflects mainly enrichment by non-forest sites such as grassland or sparse shrubs. Our results indicate that the ecological performance of habitat characteristics (and not only the woodlot area) is important for the restoration of bird diversity in woodlots, and as such should be taken into consideration by the EU’s CAP subsidy system. Moreover, if woodlot management aims to maximize the overall bird diversity—a common practice in biodiversity conservation—our results show that current practices may favor widespread forest bird species, but not the farmland birds that are more threatened in Europe. To manage the woodlot habitat for farmland birds, we suggest that microhabitat heterogeneity should be maximized.
Agricultural intensification seriously threatens European biodiversity. To mitigate this threat, farmland habitat suitability should be improved. Mid-field woodlots surrounded by intensively cultivated fields or grasslands, represent one of the promising tools for such improvement. However, woodlots can be dominated by non-native plants and their impacts on woodlot function as refugees for biodiversity remains unclear. Therefore, we studied the impact of the invasive black locust (Robinia pseudoacacia L.) on bird species richness in woodlots in intensively cultivated Central European farmland. We surveyed 27 mid-field woodlots (13 covered by native vegetation and 14 dominated by black locust) in the Czech Republic, relating the species richness of all birds, habitat specialists and habitat generalists to woodlot characteristics: black locust occurrence, distance to the main forest, age of the woodlot, vegetation structure, arthropod biomass (representing food supply for birds), surrounding habitats and type of crops in which they are embedded. Our results suggest that the woodlots covered by the black locust had lower species richness of all birds, habitat specialists and habitat generalists than the woodlots covered by native tree species. The negative impact of the invasive woody plant on birds was likely driven by changes in vegetation structure since such woodlots had lower coverage of the shrub layer and less continuous canopy. This mechanism was particularly supported in habitat generalists, whereas habitat specialists additionally showed positive relationships to the other vegetation characteristics (namely the coverage of herbs in the ground layer and the proportion of medium-sized trees). Our study shows that even though mid-field woodlots host numerous bird species, their role in the delivery of conservation benefits for breeding birds is compromised if non-native woody plants dominate the vegetation. Therefore, from the perspective of breeding birds’ conservation, the native woody plant species should be used for woodlot establishment.
The ideal free distribution theory predicts that mobile species distribute themselves among habitat patches so as to optimize their fitness. Changes in land use alter the quality of habitat patches and thereby affect the distribution of species. Following the loss of native habitat, habitat specialists are expected to move to patches where native habitat still remains in order to survive. Competition for resources in habitat remnants should consequently increase. As generalists are able to use other habitats, generalists are expected to gradually disappear in remnants in order to avoid increasing competition with specialists. Here, we test these predictions by studying the response of habitat specialist and generalist birds to land-use change in Brazil's southern grasslands. Using a space-for-time substitution approach, we surveyed bird communities in native grassland sites (~4 ha) in 31 regions (10 × 10 km) with differing levels of conversion to agriculture (1–94%). We found a higher abundance of specialists in native grassland patches with increasing agricultural cover in the region, while the total number of individuals in remnants remained constant. At the same time, the share of generalists in total abundance and total species richness decreased. To gain insights into whether these patterns could be driven by shifts in competition, we tested whether generalists that continued to co-occur with specialists in remnants, had less dietary overlap with specialists. As a consequence of community composition in remnants, a higher proportion of generalists were omnivorous and the average generalist species fed less on seeds, whereas the average specialist species fed more on seeds when agricultural cover was high in the region. Our results, therefore, support predictions of the ideal free distribution theory. Specialists that are assumed to have a low survivorship outside of their specialized habitat, distribute to remnants of this habitat when it is converted elsewhere, while generalists, being able to survive in other habitats, disappear gradually in remnants. Such a process could partly explain the segregation of habitat specialist and generalist birds observed in many agricultural landscapes. Finally, our results suggest that native habitat remnants can be important temporary refugia for specialists.
Cleared reeds are formations of reeds Phragmites australis growing at different stem density interspersed inside of bush-grass-tree masses in freshwater or brackish waters. Generally, these are considered as the early succession stage of a plant hydro series. The importance for the small-medium birds which uses these formations is huge. This is because the broad masses of reeds are reducing from the past century and birds benefit of the rich invertebrate fauna of these residual sites from the adaptive functional morphology of these birds to cope with these habitats more skillfully than other wetland birds. I summarize the habitat preferences of this vegetation type on some endangered small-medium birds at Western Mediterranean areas.
▪ Abstract A growing number of species have been transported and introduced by humans to new locations and have established self-sustaining wild populations beyond their natural range limits. Many of these species go on to have significant environmental or economic impacts. However, not all species transported and introduced to new locations succeed in establishing wild populations, and of the established species only some become widespread and abundant. What factors underlie this variation in invasion success? Here, we review progress that has been made in identifying factors underpinning invasion success from studies of bird introductions. We review what is known about the introduction, establishment, and spread of introduced bird species, focusing on comparative studies that use historical records to test hypotheses about what factors determine success at different stages in the invasion process. We close with suggestions for future research.
We used measurements of museum skins to assess morphological differences between the 22 currently recognized species of wheatear and to identify correlations between morphological features, behavioural traits and degrees of sympatry between species. Ground-dwelling species of steppe-like habitats have long tarsi, long claws and short tails; some are migratory and have long pointed wings and non-emarginated primaries (O. isabellina and O. oenanthe), while others are sedentary and have more rounded and slotted wings (O. bottae , O. heuglini and O. pileata). Vegetation-tolerant species (O. pleschanka , O. hispanica , O. cypriaca and O. deserti) have relatively long tails, short tarsi, long middle toes and long claws. The rock-dwelling species have short tarsi, long toes and short claws; they can be either relatively heavy (O. leucura and O. monticola) or light, like the wheatears inhabiting the most arid areas (O. monacha , O. leucopyga and O. alboniger). Although sedentary , the latter show intermediate characteristics between sedentary and migratory species, having relatively pointed wings with non-emarginated primaries. Together with their low wing-loadings, these traits may be related to the scarcity of resources in their habitats, which obliges them to make frequent and long flights. The clear morphological differentiation between wheatear species appears to be mainly related to their migratory and foraging habits, but seems to bear no relation to their degree of sympatry.
Seasonal movements are common in Neotropical forest birds. Species that engage in the largest movements, altitudinal and intratropical migrants, are predominantly frugivores or nectarivores of canopy/edge or dry habitats. Migration by such species may be necessitated by the high spatial and temporal variation in their resource base. We hypothesize that seasonal movements within the tropics predisposed these birds to migration out of the tropics. Indeed, most Nearctic passerine migrants are drawn from Neotropical taxa that exhibit altitudinal or intratropical migration. Conversely, taxa comprising the most sedentary group of Neotropical residents (understory insectivores) are poorly represented among Nearctic migrants. Further evidence of an evolutionary link between seasonal movements within the tropics and long-distance migration is provided by similarities in habitat use and diet between overwintering Nearctic migrants and closely related tropical residents. Both groups tend to be frugivorous/nectarivorous, inhabit "open" habitat, and engage in seasonal movements. The only difference in their movements is one of scale. These results help explain the behavior and ecology of Nearctic birds overwintering in the Neotropics.
Functional morphology of the wings, legs, and tail of Parus ater, P. montanus, P. cristatus, Regulus regulus , and Certhia familiaris is analysed and compared, and correlations are sought with locomotion pattern and feeding station selection. These species are treated together because they are sympatric, occur in the same habitat, and partly overlap in feeding station selection, as well as in food selection. Where possible, the selective advantage of a feature is judged in terms of the energy savings that it makes possible with the respective locomotion pattern. P. ater has relatively low weight, low wing loading and long wing span. It is adapted to slow flight and high manoeuvrability. P. montanus has high wing loading, relatively short wings and long tail. It is not well adapted to manoeuvrable flight, but more to a clinging and climbing behaviour. P. cristatus has the highest wing loading of the species. It has short and broad wings, and rather short tail in relation to the body size. It is not adapted to slow manoeuvrable flight. It hops about on the branches or ground to a greater extent than the other species. Further, by its mere size, it is more adapted to low temperatures than the other species. R. regulus and C. familiaris have the lowest wing loadings and shortest arm wings in relation to the total length of the wings. C. familiaris also has relatively long span. The longer the span the lower the induced power, which forms a big part of the power consumption in hovering. The induced power per unit body mass is lowest in C. familiaris (1.13 W kg ⁻¹ ), and lower in R. regulus (1.19 W kg ⁻¹ ) and P. ater (1.21 W kg ⁻¹ ) than in P. montanus (1.28 W kg-1 ) and P. cristatus (1.31 W kg ⁻¹ ). The ratio (length of hand wing) / (length of arm wing) is 3.0 and 2.9 in C. familiaris and R. regulus , respectively, and 2.4- 2.6 in the other species. The shorter the arm wing is in relation to the total length of the wing, the more proximally the main mass of the wing will be located, and the less the inertial power and inertial loads on the wing skeleton become. The inertial power is another power drain in hovering. Therefore, because of their low wing loading and short arm wings, R. regulus and C. familiaris are particularly well adapted to slow flight and to hovering. P. ater and R. regulus are partly migratory and, therefore, should benefit more by long wing span than the other species. In fact, P. ater has relatively long span while R. regulus has not. The relatively short span in R. regulus is probably an adaptation for manoeuvrability and practicability in the dense vegetation where it usually forages. As related to body size, C.familiaris has the shortest legs, longest tail and toes, and longest and most curved claws, features that are obvious adaptations to climbing locomotion. The reduction of the leg length in the course of adaptations for climbing has affected the tibiotarsus most and the femur least. It is especially important for the tibiotarsus to be short to minimize the muscle force needed for clinging on a vertical trunk, and also to shorten the legs with least loss of step length. The tail is used as support in climbing (although not during the latter part of the power stroke). The longer the tail is, the less the horizontal force between claw and bark becomes, and, hence, the less the energy expenditure during the power stroke in climbing. The three tits have almost the same relative leg length. R. regulus has the longest legs in relation to body size. P. ater, P. montanus and C.familiaris have relatively short tarsometatarsus. Further, P. ater and R. montanus have long muscle lever arm of the flexor of the tarsometatarsus. Both characters are adaptations for hanging under branches and/or for climbing. Birds with need of rapid leg movements should have a short lever arm for the flexor muscle of the tarsometatarsus. During foraging R. regulus, P. cristatus and C.familiaris use their legs more for hopping, which requires speed of leg movements, and less for hanging than do P. ater and P. montanus , and they also have shorter muscle lever arms than the latter two species. In C.familiaris the short tarsometatarsus thus is adapted for hanging whereas the short lever arm of the muscle force is not. When the bird is hanging under a perch with 45° flexion of the tarsometatarsus relative to the tibiotarsus, then the muscle force (of M. tibialis anticus) per unit body mass is about 36, 44, 45 and 54 % larger in R. regulus than in P. cristatus, P. ater, C.familiaris and P. montanus , respectively. The corresponding differences between P. cristatus and the three latter species are 6, 7 and 14%. A clustering process was used to illustrate more clearly the phenetic resemblances among the species regarding the morphology of the locomotor apparatuses. As regards the wing skeleton the tits form a group, and C.familiaris is more similar to the tits than to R. regulus . The wing-form phenogram shows that P. montanus and P. cristatus resemble each other most, that P. ater is intermediary between these tits and R. regulus , and that C. familrsis most similar to R. regulus . The phenogram based on the form of the leg and foot shows that the tits resemble each other most and that R. regulus and C. familiaris are rather unlike the tits and also very unlike each other. In the tits, the skeleton of the legs is more diverse than that of the wings, and seems to have been subjected to more divergent selection pressures than the wing skeleton. As regards aerial locomotion in the three tits, the adaptation to different niches, and hence to different flight patterns, have led to divergent evolution of the wing feathers rather than of the wing skeleton. The pattern for all five species together is most diverse in leg characters and wing form and least diverse in the wing skeleton.
It is often claimed that we do not understand the forces driving the global diversity gradient. However, an extensive literature suggests that contemporary climate constrains terrestrial taxonomic richness over broad geographic extents. Here, we review the empirical literature to examine the nature and form of the relationship between climate and richness. Our goals were to document the support for the climatically based energy hypothesis, and within the constraints imposed by correlative analyses, to evaluate two versions of the hypothesis: the productivity and ambient energy hypotheses. Focusing on studies extending over 800 km, we found that measures of energy, water, or water-energy balance explain spatial variation in richness better than other climatic and non-climatic variables in 82 of 85 cases. Even when considered individually and in isolation, water/ energy variables explain on average over 60% of the variation in the richness of a wide range of plant and animal groups. Further, water variables usually represent the strongest predictors in the tropics, subtropics, and warm temperate zones, whereas energy variables (for animals) or water-energy variables (for plants) dominate in high latitudes. We conclude that the interaction between water and energy, either directly or indirectly (via plant pro- ductivity), provides a strong explanation for globally extensive plant and animal diversity gradients, but for animals there also is a latitudinal shift in the relative importance of ambient energy vs. water moving from the poles to the equator. Although contemporary climate is not the only factor influencing species richness and may not explain the diversity pattern for all taxonomic groups, it is clear that understanding water-energy dynamics is critical to future biodiversity research. Analyses that do not include water-energy variables are missing a key component for explaining broad-scale patterns of diversity.
We present a European land-only daily high-resolution gridded data set for precipitation and minimum, maximum, and mean surface temperature for the period 1950–2006. This data set improves on previous products in its spatial resolution and extent, time period, number of contributing stations, and attention to finding the most appropriate method for spatial interpolation of daily climate observations. The gridded data are delivered on four spatial resolutions to match the grids used in previous products as well as many of the rotated pole Regional Climate Models (RCMs) currently in use. Each data set has been designed to provide the best estimate of grid box averages rather than point values to enable direct comparison with RCMs. We employ a three-step process of interpolation, by first interpolating the monthly precipitation totals and monthly mean temperature using three-dimensional thin-plate splines, then interpolating the daily anomalies using indicator and universal kriging for precipitation and kriging with an external drift for temperature, then combining the monthly and daily estimates. Interpolation uncertainty is quantified by the provision of daily standard errors for every grid square. The daily uncertainty averaged across the entire region is shown to be largely dependent on the season and number of contributing observations. We examine the effect that interpolation has on the magnitude of the extremes in the observations by calculating areal reduction factors for daily maximum temperature and precipitation events with return periods up to 10 years
Biotic homogenization (BH) is a process whereby some species (losers) are systematically replaced by others (winners). While this process has been related to the effects of anthropogenic activities, whether and how BH is occurring across regions and the role of native species as a driver of BH has hardly been investigated. Here, we examine the trend in the community specialization index (CSI) for 234 native species of breeding birds at 10 111 sites in six European countries from 1990 to 2008. Unlike many BH studies, CSI uses abundance information to estimate the balance between generalist and specialist species in local assemblages. We show that bird communities are more and more composed of native generalist species across regions, revealing a strong, ongoing BH process. Our result suggests a rapid and non-random change in community composition at a continental scale is occurring, most likely driven by anthropogenic activities.
Variation in dietary niche breadth among species is supposed to result from interactions within communities, but also from phylogenetic conservatism as well as constraints set by other traits. Here, we explore variation of dietary niche breadth across land birds occurring in Eastern Germany in correlation with phylogeny and traits like distributional range size, abundance, habitat range, body size, migratory behaviour and sexual dimorphism. First, we found a clear indication of phylogenetic conservatism: about half of the variation in dietary niche breadth across species was due to variation between families and genera. Habitat range, distributional range size of species in Eastern Germany and abundance did not correlate with dietary niche breadth. The significance of the correlation of dietary niche breadth with body size, distributional range size of species in Europe and plumage dichromatism depends on the details of the analyses. Nevertheless, even after controlling for phylogeny, we found robust correlations of dietary niche breadth versus migratory behaviour as well as sexual size dimorphism: species with a narrow dietary niche tend to be migratory and, in species with a broad dietary niche, males tend to be larger than females.
A growing number of species have been transported and introduced by humans to new locations and have established self-sustaining wild populations beyond their natural range limits. Many of these species go on to have significant environ-mental or economic impacts. However, not all species transported and introduced to new locations succeed in establishing wild populations, and of the established species only some become widespread and abundant. What factors underlie this variation in invasion success? Here, we review progress that has been made in identifying factors underpinning invasion success from studies of bird introductions. We review what is known about the introduction, establishment, and spread of introduced bird species, focusing on comparative studies that use historical records to test hypotheses about what factors determine success at different stages in the invasion process. We close with suggestions for future research.
Aim Increased specialization has been hypothesized to facilitate local coexistence and thus high species richness, but empirical evaluations of the richness–specialization relationships have been relatively scant. Here, we provide a first assessment of this relationship for terrestrial bird assemblages at global extent and from fine to coarse grains.
Location World‐wide.
Methods We use two indices of specialization that describe species‐level resource use: diet and habitat specialization. The relationship between richness and mean assemblage‐level specialization was independently assessed at realm, biome‐realm, 12,100 km ² equal‐area grid cells and fine‐grained scales. To identify assemblages that are diverse relative to environmental conditions we: (1) applied quantile regressions, (2) statistically accounted for other environmental variables which may constrain richness, and (3) parsed the data according to the residuals of a model relating species richness to the environmental variables.
Results Assemblage species richness increases with both measures of specialization at all scales. Statistically, richness appears constrained by levels of specialization, with the highest richness values only found in specialized assemblages. Richness is positively associated with specialization even after accounting for gradients in resource availability. Net primary productivity and assemblage specialization have complementary statistical effects on assemblage species richness. Contrary to expectations based on niche partitioning of local resources, the relationship between specialization and richness is steep even at coarse scales.
Main conclusions The results demonstrate that for an entire clade, totalling > 9000 species, specialization and species richness are related, at least for diverse assemblages. The strong patterns observed across scales suggest that this relationship does not solely originate from (1) limits on coexistence in present‐day assemblages, or (2) increased specialization in richer assemblages imposed by species’ abilities to partition ecological space. Instead, regional‐scale influences on the species pool may determine much of the observed relationship between richness and specialization. Although causal attribution is not straightforward, these findings support the idea that, for the scale of our analysis, specialization may be related to the past origination of high‐diversity assemblages, rather than their contemporary assembly.
1. Ecological specialization is one of the main concepts in ecology and conservation. However, this concept has become highly context‐dependent and is now obscured by the great variability of existing definitions and methods used to characterize ecological specialization.
2. In this study, we clarify this concept by reviewing the strengths and limitations of different approaches commonly used to define and measure ecological specialization. We first show that ecological specialization can either be considered as reflecting species’ requirements or species’ impacts. We then explain how specialization depends on species‐specific characteristics and on local and contingent environmental constraints. We further show why and how ecological specialization should be scaled across spatial and temporal scales, and from individuals to communities.
3. We then illustrate how this review can be used as a practical toolbox to classify widely used metrics of ecological specialization in applied ecology, depending on the question being addressed, the method used, and the data available.
4. Synthesis and applications . Clarifying ecological specialization is useful to make explicit connections between several fields of ecology using the niche concept. Defining this concept and its practical metrics is also a crucial step to better formulate predictions of scientific interest in ecology and conservation. Finally, understanding the different facets of ecological specialization should facilitate to investigate the causes and consequences of biotic homogenization and to derive relevant indicators of biodiversity responses to land‐use changes.
Predicting species' responses to the combined effects of habitat and climate changes has become a major challenge in ecology and conservation biology. However, the effects of climatic and habitat gradients on species distributions have generally been considered separately. Here, we explore the relationships between the habitat and thermal dimensions of the ecological niche in European common birds. Using data from the French Breeding Bird Survey, a large-scale bird monitoring program, we correlated the habitat and thermal positions and breadths of 74 bird species, controlling for life history traits and phylogeny. We found that cold climate species tend to have niche positions in closed habitats, as expected by the conjunction of the biogeographic history of birds' habitats, and their current continent-scale gradients. We also report a positive correlation between thermal and habitat niche breadths, a pattern consistent with macroecological predictions concerning the processes shaping species' distributions. Our results suggest that the relationships between the climatic and habitat components of the niche have to be taken into account to understand and predict changes in species' distributions.
The question 'what renders a species extinction prone' is crucial to biologists. Ecological specialization has been suggested as a major constraint impeding the response of species to environmental changes. Most neoecological studies indicate that specialists suffer declines under recent environmental changes. This was confirmed by many paleoecological studies investigating longer-term survival. However, phylogeneticists, studying the entire histories of lineages, showed that specialists are not trapped in evolutionary dead ends and could even give rise to generalists. Conclusions from these approaches diverge possibly because (i) of approach-specific biases, such as lack of standardization for sampling efforts (neoecology), lack of direct observations of specialization (paleoecology), or binary coding and prevalence of specialists (phylogenetics); (ii) neoecologists focus on habitat specialization; (iii) neoecologists focus on extinction of populations, phylogeneticists on persistence of entire clades through periods of varying extinction and speciation rates; (iv) many phylogeneticists study species in which specialization may result from a lack of constraints. We recommend integrating the three approaches by studying common datasets, and accounting for range-size variation among species, and we suggest novel hypotheses on why certain specialists may not be particularly at risk and consequently why certain generalists deserve no less attention from conservationists than specialists.
Most empirical and theoretical studies of resource use and population dynamics treat conspecific individuals as ecologically equivalent. This simplification is only justified if interindividual niche variation is rare, weak, or has a trivial effect on ecological processes. This article reviews the incidence, degree, causes, and implications of individual-level niche variation to challenge these simplifications. Evidence for individual specialization is available for 93 species distributed across a broad range of taxonomic groups. Although few studies have quantified the degree to which individuals are specialized relative to their population, between-individual variation can sometimes comprise the majority of the population's niche width. The degree of individual specialization varies widely among species and among populations, reflecting a diverse array of physiological, behavioral, and ecological mechanisms that can generate intrapopulation variation. Finally, individual specialization has potentially important ecological, evolutionary, and conservation implications. Theory suggests that niche variation facilitates frequency-dependent interactions that can profoundly affect the population's stability, the amount of intraspecific competition, fitness-function shapes, and the population's capacity to diversify and speciate rapidly. Our collection of case studies suggests that individual specialization is a widespread but underappreciated phenomenon that poses many important but unanswered questions.
Analysis of Phylogenetics and Evolution (APE) is a package written in the R language for use in molecular evolution and phylogenetics.
APE provides both utility functions for reading and writing data and manipulating phylogenetic trees, as well as several advanced
methods for phylogenetic and evolutionary analysis (e.g. comparative and population genetic methods). APE takes advantage
of the many R functions for statistics and graphics, and also provides a flexible framework for developing and implementing
further statistical methods for the analysis of evolutionary processes.
Availability: The program is free and available from the official R package archive at http://cran.r-project.org/src/contrib/PACKAGES.html#ape. APE is licensed under the GNU General Public License.
The order Passeriformes ("perching birds") comprises extant species diversity comparable to that of living mammals. For over a decade, a single phylogenetic hypothesis based on DNA-DNA hybridization has provided the primary framework for numerous comparative analyses of passerine ecological and behavioral evolution and for tests of the causal factors accounting for rapid radiations within the group. We report here a strongly supported phylogenetic tree based on two single-copy nuclear gene sequences for the most complete sampling of passerine families to date. This tree is incongruent with that derived from DNA-DNA hybridization, with half of the nodes from the latter in conflict and over a third of the conflicts significant as assessed under maximum likelihood. Our historical framework suggests multiple waves of passerine dispersal from Australasia into Eurasia, Africa, and the New World, commencing as early as the Eocene, essentially reversing the classical scenario of oscine biogeography. The revised history implied by these data will require reassessment of comparative analyses of passerine diversification and adaptation.
The question of how birds migrate over enormous distances with apparently minimal guidance continues to excite both professional and amateur ornithologists. Nearly ten years have elapsed since Peter Berthold, a leading researcher in the field, wrote the first edition of this highly readable and fascinating book. During that time the field has advanced by strides, so that this new edition has been extensively revised, expanded, and updated. No other book exists that brings together the vast amount of information that is available on the subject of bird migration, so that the book will be an inspiration to birdwatchers, naturalists, and ornithologists alike.
Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes.
[Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].
AimAn important, unresolved question in macroecology is to understand the immense inter-specific variation in geographic range sizes. While species traits such as fecundity or body size are thought to affect range sizes, a general understanding on how multiple traits jointly influence them is missing. Here, we test the influence of a multitude of species traits on global range sizes of European passerine birds in order to better understand possible mechanisms behind macroecological relationships. LocationGlobal. Methods
We evaluated the effect of life-history traits (fecundity, dispersal ability), ecological traits (habitat niche, diet niche, migratory behaviour, migratory flexibility) and a morphological trait (body size) on the global range sizes of 165 European passerines. We identified hypotheses from the literature relating traits to range size and used path analysis to test them. ResultsFecundity, dispersal ability and habitat niche breadth had a direct positive effect on range size. Diet niche position had a direct negative effect on range size. Habitat niche breadth also had an indirect positive effect via higher fecundity. Migratory behaviour had an indirect positive effect via better dispersal ability. Body size had a strong positive direct effect which was reduced by negative indirect effects via several other traits. Main conclusionsGeographic range sizes of European passerines were influenced by life-history traits (fecundity and dispersal ability), ecological traits (habitat niche breadth, diet niche position and migratory behaviour) and by body size. Traits influenced range size both directly and indirectly. Body size effects were particularly complex, with positive and negative effects acting over different pathways. We show that it is necessary to disentangle the direct and indirect influence of multiple traits on range size to better elucidate the mechanisms that generate macroecological relationships.
In most long-distance migratory birds, juveniles migrate without their parents and so are likely to lack detailed knowledge of where to go. This suggests the potential for stochasticity to affect their choice of wintering area at a large scale (> 1000 km). Adults, in contrast, may re-use non-breeding sites that promote their survival, so removing uncertainty from their subsequent migrations. I review the evidence for large-scale stochastic juvenile site selection followed by adult site fidelity, and then develop a ‘serial-residency’ hypothesis based on these two traits as a framework to explain both the migratory connectivity and the population dynamics of migrant birds and how these are affected by environmental change. Juvenile stochasticity is apparent in the age-dependent effects of weather or experimental displacement on the outcome of migration and in the very wide variation in the destinations of individuals originating from the same area. Adults have been shown to be very faithful to their wintering grounds and even to staging sites. The serial residency hypothesis predicts that migrants that show these two traits will rely on an individually unique but fixed series of temporally and spatially linked sites to complete their annual cycle. As a consequence, migratory connectivity will be apparent at a very small scale for individuals, but only at a large scale for a population, and juveniles are predicted to occur more often at less suitable sites than adults, so that survival will be lower for juveniles. Migratory connectivity will arise only through spatial and temporal autocorrelation with local environmental constraints, particularly on passage, and the distribution and age structure of the population may reflect past environmental constraints. At least some juveniles will discover suitable habitat that they may re-use as adults, thus promoting overall population-level resilience to environmental change, and suggesting value in site-based conservation. However, because migratory connectivity only acts on a large scale, any population of migrants will contain individuals that encounter a change in suitability somewhere in their non-breeding range, so affecting average survival. Differences in population trends will therefore reflect variation in local breeding output added to average survival from wintering and staging areas. The latter is likely to be declining given increasing levels of environmental degradation throughout Africa. Large-scale migratory connectivity also has implications for the evolutionary ecology of migrants, generally because this is likely to lead to selection for generalist traits.
The extent to which species’ ecological and phylogenetic relatedness shape their co-occurrence patterns at large spatial scales remains poorly understood. By quantifying phylogenetic assemblage structure within geographic ranges of >8000 bird species, we show that global co-occurrence patterns are linked – after accounting for regional effects – to key ecological traits reflecting diet, mobility, body size and climatic preference. We found that co-occurrences of carnivorous, migratory and cold-climate species are phylogenetically clustered, whereas nectarivores, herbivores, frugivores and invertebrate eaters tend to be more phylogenetically overdispersed. Preference for open or forested habitats appeared to be independent from the level of phylogenetic clustering. Our results advocate for an extension of the tropical niche conservatism hypothesis to incorporate ecological and life-history traits beyond the climatic niche. They further offer a novel species-oriented perspective on how biogeographic and evolutionary legacies interact with ecological traits to shape global patterns of species coexistence in birds.
Aim
Climate is widely recognized as a major predictor of species richness patterns along large‐scale environmental gradients. Nevertheless, the mechanisms by which climate influences species richness are still a matter of debate. We disentangle whether climate influences species richness of birds directly via physiological limitations or indirectly via vegetation structure or the availability of food resources.
Location
M ount K ilimanjaro, T anzania.
Methods
We recorded bird species richness along an elevational gradient from 870 to 4550 m a.s.l. We quantified local climatic conditions, vegetation structure and the availability of food resources, and applied path analysis to disentangle their direct and indirect effects on species richness of all birds, frugivores and insectivores.
Results
Overall, we recorded 2945 individuals from 114 bird species. Species richness of all birds was closely correlated with temperature, vegetation structure and invertebrate biomass and both direct and indirect (via vegetation structure and availability of food resources) climatic effects were important for the diversity of the whole, trophically heterogeneous bird community. The species richness of insectivorous birds was linked to vegetation structure and invertebrate biomass, while the richness of frugivores was strongly associated with fruit abundance. Climatic factors influenced bird species richness of both avian feeding guilds exclusively indirectly via vegetation structure and availability of food resources.
Main conclusions
We reveal the importance of trophic interactions for generating species richness patterns along large‐scale environmental gradients. Our results challenge the general assumption that temperature and water availability influence species richness mostly directly, and underscore the importance of vegetation structure and the availability of food resources as principal mediators of climatic effects on species richness patterns on macroecological scales.
1. Relationships between foraging strategy, flight performance and wing shape in animals can be demonstrated with the use of aerodynamic theory. The optimal morphology is dictated not only by foraging behaviour and habitat selection but also by size of prey and migratory habits, as well as flight display. Here I demonstrate how changes in body size and structure of wings and tail affect the optimal flight speeds and power required to fly. 2. Long-tailed birds flying with their tails hanging downwards-backwards (e.g. widowbirds) are predicted to fly more slowly than short-tailed birds to save energy or to have larger wings (broader and/or longer wings giving lower wing loading) to compensate for increased tail drag during flight. Assuming that the tail length is five times as long in a long-tailed bird than in a short-tailed (normal) one, the minimum power and maximum range power would be about 30% higher in the long-tailed bird and the corresponding speeds about 40% slower. Ignoring wing inertial loads as a cost (inertial power) the corresponding percentages would become 16-18% higher powers and slower speeds. 3. I predict that members of a bird family that display in hovering or vertical take-off flights should not have elongated wings if wing inertia is important. In contrast to most other widowbird species, males of Jackson's widowbird (Euplectes jacksoni) do not have elongated wings (Anderson 1992), although they have particularly costly tails (Thomas 1993). This species has abandoned forward flight display and instead uses a vertical take-off and hovering flight display. Inertial costs appear to explain this result. 4. An increase in weight causes an increase in wing loading, which in turn requires higher flight speed for production of enough lift. A 50% increase in body mass (as fat, an egg or a fetus inside the body), would increase P(mr) and P(mp) by about 45-50% and V(mr) and V(mp) by about 20-25% (symbols defined in Fig. 1), when inertial power is taken to be zero. 5. A bird or bat carrying prey in the beak/mouth or claws should use about the same speed for minimization of flight costs as when flying without prey. 6. For low flight costs, and assuming a perfect elastic storage (zero inertial power), fast-flying species should benefit from short, narrow, high-aspect-ratio wings, hovering species should have long wings and slow-flying species should have larger wings (lower wing loadings) but with no particular demands on the aspect ratio. Ignoring inertial power the best flight economy is attained by the combination of a low wing loading (enabling slow flight) and high aspect ratio (Norberg & Rayner 1987; Norberg 1990). If we assume that inertial power is an important cost in hovering, a hovering animal should have short wings to minimize mechanical power.
The range of resources that a species uses (i.e. its niche breadth) might determine the geographical area it can occupy, but consensus on whether a niche breadth-range size relationship generally exists among species has been slow to emerge. The validity of this hypothesis is a key question in ecology in that it proposes a mechanism for commonness and rarity, and if true, may help predict species' vulnerability to extinction. We identified 64 studies that measured niche breadth and range size, and we used a meta-analytic approach to test for the presence of a niche breadth-range size relationship. We found a significant positive relationship between range size and environmental tolerance breadth (z = 0.49), habitat breadth (z = 0.45), and diet breadth (z = 0.28). The overall positive effect persisted even when incorporating sampling effects. Despite significant variability in the strength of the relationship among studies, the general positive relationship suggests that specialist species might be disproportionately vulnerable to habitat loss and climate change due to synergistic effects of a narrow niche and small range size. An understanding of the ecological and evolutionary mechanisms that drive and cause deviations from this niche breadth-range size pattern is an important future research goal.
Excerpt
This concluding survey1 of the problems considered in the Symposium naturally falls into three sections. In the first brief section certain of the areas in which there is considerable difference in outlook are discussed with a view to ascertaining the nature of the differences in the points of view of workers in different parts of the field; no aspect of the Symposium has been more important than the reduction of areas of dispute. In the second section a rather detailed analysis of one particular problem is given, partly because the question, namely, the nature of the ecological niche and the validity of the principle of niche specificity has raised and continues to raise difficulties, and partly because discussion of this problem gives an opportunity to refer to new work of potential importance not otherwise considered in the Symposium. The third section deals with possible directions for future research.
The Demographic
Whether biotic interactions limit geographic ranges has long been controversial, and traditional analyses of static distribution patterns have made little progress towards resolving this debate. Here, we use a novel phylogenetic approach to test whether biotic interactions constrain the transition to secondary sympatry following speciation. Applying this temporal framework to a diverse clade of passerine birds (Furnariidae), we reject models of geographic range overlap limited purely by dispersal or environmental constraints, and instead show that rates of secondary sympatry are positively associated with both the phylogenetic and morphological distance between species. Thus, transition rates to sympatry increase with time since divergence and accelerate as the ecological differences between species accumulate. Taken together, these results provide strong empirical evidence that biotic interactions - and primarily ecological competition - limit species distributions across large spatial and temporal scales. They also offer phylogenetic and trait-based metrics by which these interactions can be incorporated into ecological forecasting models.
Capsule Expert‐based classification of bird species as habitat specialists and as generalists agrees with objective measures of species’ habitat requirements based on large‐scale monitoring data.Aims To compare habitat specialization of 137 common bird species breeding in the Czech Republic using three different measures and to test their relationships to species’ abundance and habitat associations.Methods Data on bird abundance and surveyed habitats were collected through a standardized monitoring scheme of common breeding species in the Czech Republic. From these data we calculated a quantitative species specialization index (SSI). Canonical correspondence analysis (CCA) was applied to calculate species’ habitat niche breadth and the level of association of each species to the main habitats. A panel of 11 local bird experts classified each species as habitat generalist or habitat specialist.Results Species classified as habitat specialists by expert opinion showed higher habitat specialization according to the SSI, as well as according to CCA‐based habitat niche breadth. These species were also more closely associated with one of the main habitat types. These relationships were significant even after controlling for abundance.Conclusions As expert opinion accords with the level of species’ habitat specialization expressed using two quantitative objective measures, we suggest that these characteristics reflect real interspecific variation in the breadth of habitat requirements in birds. Interspecific differences in habitat specialization are not caused solely by the variability in abundance among species.
Current global patterns of biodiversity result from processes that operate over both space and time and thus require an integrated macroecological and macroevolutionary perspective. Molecular time trees have advanced our understanding of the tempo and mode of diversification and have identified remarkable adaptive radiations across the tree of life. However, incomplete joint phylogenetic and geographic sampling has limited broad-scale inference. Thus, the relative prevalence of rapid radiations and the importance of their geographic settings in shaping global biodiversity patterns remain unclear. Here we present, analyse and map the first complete dated phylogeny of all 9,993 extant species of birds, a widely studied group showing many unique adaptations. We find that birds have undergone a strong increase in diversification rate from about 50 million years ago to the near present. This acceleration is due to a number of significant rate increases, both within songbirds and within other young and mostly temperate radiations including the waterfowl, gulls and woodpeckers. Importantly, species characterized with very high past diversification rates are interspersed throughout the avian tree and across geographic space. Geographically, the major differences in diversification rates are hemispheric rather than latitudinal, with bird assemblages in Asia, North America and southern South America containing a disproportionate number of species from recent rapid radiations. The contribution of rapidly radiating lineages to both temporal diversification dynamics and spatial distributions of species diversity illustrates the benefits of an inclusive geographical and taxonomical perspective. Overall, whereas constituent clades may exhibit slowdowns, the adaptive zone into which modern birds have diversified since the Cretaceous may still offer opportunities for diversification.
1. Positive relationships between the local abundance and the range size of the species in a taxonomic assemblage are very general. 2. Explanations for these relationships typically focus on two mechanisms, based on differences in the niche breadths of species, or metapopulation dynamics. Others have, however, also been suggested. 3. Here we identify and clarify all the principal mechanisms proposed to explain positive interspecific abundance-range size relationships. We critically assess the assumptions and predictions that they make, and the evidence in support of them. 4. A number of predictions are common to all of the biological (as opposed to artefactual) mechanisms, but the combination of predictions and assumptions made by each is unique, suggesting that, in principle, conclusive tests of all of the mechanisms are possible. 5. On present evidence, no single mechanism has unequivocal support. We discuss reasons why this might be the case.
Aim The species–area relationship has been applied in the conservation context to predict monotonic species richness declines as natural area is converted to human-dominated land covers. However, some conversion of natural cover could introduce new habitat types and allow new open habitat species to occur. Moreover, decelerating richness–area relationships suggest that, as natural area is converted to human-dominated covers, more species will be added to the rare habitat than are lost from the common one. Area effects and increased habitat diversity could each lead to a peaked relationship between species richness and the relative amount of natural area. The purpose of this study is to quantify the effect on avian species richness of conversion of natural area to human-dominated land cover.
Aim Worldwide, functional homogenization is now considered to be one of the most prominent forms of biotic impoverishment induced by current global changes. Yet this process has hardly been quantified on a large scale through simple indices, and the connection between landscape disturbance and functional homogenization has hardly been established. Here we test whether changes in land use and landscape fragmentation are associated with functional homogenization of bird communities at a national scale.
Location France.
Methods We estimated functional homogenization of a community as the average specialization of the species present in that community. We studied the spatial variation of this community specialization index (CSI) using 1028 replicates from the French Breeding Bird Survey along spatial gradients of landscape fragmentation and recent landscape disturbance, measured independently, and accounting for spatial autocorrelation.
Results The CSI was very sensitive to both measures of environmental degradation: on average, 23% of the difference in the CSI values between two sample sites was attributed to the difference in fragmentation and the disturbance between sites. This negative correlation between CSI and sources of landscape degradation was consistent over various habitats and biogeographical zones.
Main conclusions We demonstrate that the functional homogenization of bird communities is strongly positively correlated to landscape disturbance and fragmentation. We suggest that the CSI is particularly effective for measuring functional homogenization on both local and global scales for any sort of organism and with abundance or presence–absence data.
Few studies have examined how life history traits and the climate envelope influence the ability of species to respond to climate change and habitat degradation. In this study, we test whether 18 species-specific variables, related to the climate envelope, ecological envelope and life history, could predict recent population trends (over 17 years) of 71 common breeding bird species in France. Habitat specialists were declining at a much higher rate than generalists, a sign that habitat quality is decreasing globally. The lower the thermal maximum (temperature at the hot edge of the climate envelope), the more negative are the population trends and the less tolerant these species are climate warming, regardless of the thermal range over which these species occur. The life history trait ‘the number of broods per year’ was positively related to recent trends, suggesting that single-brooded species might be more sensitive to advances in food peak due to climate change, as it increases the risk of mistiming their single-breeding event. Annual fecundity explained long-term declines, as it is a good proxy for most other demographic rates, with shorter-lived species being more sensitive to global change: individuals of species with higher fecundity might have too short a life to learn to adapt to directional changes in their environment. Finally, there was evidence that natal dispersal was a predictor of recent trends, with species with high natal dispersal experiencing smaller population declines than species with low natal dispersal. This is expected if the higher the natal dispersal, the larger the ability to shift spatially when facing changes in local habitat or climate, in order to track optimal conditions and adapt to global change. Identifying decline-promoting factors allow us to infer mechanisms responsible for observed declines in wild bird populations facing global change, and by doing so allow for a more pre-emptive approach to conservation planning.
Two of the most prominent explanations for a positive interspecific relationship between local abundance and regional distribution are the resource breadth and the resource availability hypotheses. Here we test these hypotheses by characterising habitat use of British breeding birds using extensive census and environmental data. A group of 85 bird species was considered for study along with 34 land use or environmental variables, which were used to generate four ordination axes by Canonical Correspondence Analysis. Measures of niche breadth and position were derived from these synthetic environmental axes using standard procedures. Across species, none of five measures of abundance and distribution chosen were correlated with niche breadth, whereas four out of five of these measures were correlated negatively with niche position. Repeating the analyses using a method designed to control for phylogenetic non-independence confirmed these general patterns. Birds that tended to use resources that were more atypical of the environment tended to be rarer and thinly distributed, while those using typical resources were common and widely distributed. Performing the analyses on subsets of the data based on species sample sizes did not alter the conclusions. On the assumption that our analyses properly capture patterns of niche use by birds, we find little support for the resource breadth hypothesis, but considerable support for the resource availability hypothesis.
We infer from the literature that migratory habits of birds evolved in various phylogenetic lineages and biogeographical contexts, either after gradual range expansion into seasonal habitats, or due to environmental changes within established breeding ranges. Shifts of breeding ranges are the results of interactions between colonization due to dispersal and extinction due to deteriorating conditions. Range expansions provide a platform for the evolution of migration from the newly colonized areas towards seasonally favourable non-breeding areas. A comparison of palaeoclimatic changes with concurrent evolution and distribution of passerine birds suggests that at least some of the basic genera of the Passerida radiated on the northern continents when quasi-tropical or subtropical climates prevailed. The Passerida may be a special case, but they suggest that ‘tropical origin’ does not necessarily imply a ‘southern origin’ of migratory species. Climate deterioration required adaptations either towards on-site survival under harsh conditions or towards escape movements allowing improved non-breeding survival in less seasonal climates or with reversed seasonality. Taxon-specific life-history traits and environmental conditions favoured either sedentary or migratory lines of adaptation. Repeated climate variation induced range shifts and concurrent increases or decreases in the expression of migratory behaviour. Two examples of waders suggest that the principle of range shift, followed by the development of migratory habits, is also applicable for other taxonomic groups.
The analysis of a local community of forest passerines (13 species) using phylogenetic contrasts shows a correlation between body size of bird species and mean prey size, minimum prey size, maximum prey size and the size range of dietary items. This suggests that larger birds drop small prey taxa from their prey list, because of the difficulty of capturing very small prey, for energetic reasons or because of microhabitat usage. We find some support for the third hypothesis. Dietary niche breadth calculated across prey taxa is not related to body size. Dietary niche breadth, however, is correlated with size-corrected measurements of the bill and locomotor apparatus. Long and slender bills increase the dietary niche breadth. Thus subtle differences constrain foraging and the techniques of extracting certain prey taxa form crevices. Dietary niche breadth and foraging diversity are positively correlated with population density: at least locally dietary generalists occur at higher breeding densities than specialists.
Previous ecological studies of Palearctic passerine migrants in Africa have claimed to reveal some general features with respect
to habitat use, foraging ecology and interspecific relationships with Afrotropical residents. In this review we discuss apparent
contradictions between earlier generalisations and more recent results from more detailed field studies and explore in which
areas our ecological knowledge and theoretical understanding remain poor and have given rise to misconceptions. For example,
it has been claimed that migrants use structurally more diverse and open habitats and that they forage higher and in more
peripheral parts of the vegetation than their ecologically similar Afrotropical counterparts, yet in the past these characteristics
were often not clearly defined and not always correlated in practice. It has also been stated that migrants are more flexible
in habitat use, occupying a wider range of habitat types and employing a higher diversity of foraging techniques, both of
which were assumed to be adaptations to permit coexistence with Afrotropical residents by using untapped resources that are
only seasonally available. Yet results from studies of the role of competition in shaping migrant-resident communities remain
largely unconvincing. While flexibility may facilitate migrant-resident coexistence, it may also favour the evolution of migration
because specialists are less able to use their advantages in different environments. We note that definitions of flexibility
and specialisation may themselves depend on the ecological or evolutionary approach adopted by researchers. We conclude that
few generalisations can safely be made about the ecology of Palearctic migrants in Africa and that adaptive explanations for
the behaviours observed are largely lacking, as are studies of the fitness consequences of different migrant strategies such
as have been conducted in the Nearctic-Neotropical migration system.
We present the first continent-wide analysis of the population trends of European breeding birds to show that populations of Afro-Palearctic migrant birds have shown a pattern of sustained, often severe, decline. The mean trend of inter-continental migrants was significantly negative between 1970 and 1990 and non-significantly so between 1990 and 2000. Mean population trends were positively correlated between periods, suggesting little change in the trajectory of most migrant species’ populations over this 30-year period. In both periods, trends of inter-continental migrants were significantly more negative than those of short-distance migrants or residents. This negative trend appeared to be largely, although not entirely, due to declines in species wintering in dry, open habitats in Africa. Analyses of trends of 30 closely related pairs of species, one a long-distance migrant and the other not, indicated significantly more negative trends in the former, irrespective of breeding habitat. Conservation action to address these declines is required under the Convention on Migratory Species and the Pan-European Biological and Landscape Diversity Strategy, to which most European countries are signatories and which aim, respectively, to conserve migratory species and to halt the loss of biodiversity by 2010. Our results indicate that more conservation action may be required outside Europe to achieve these targets. Further research is needed to assess whether the declines are caused by factors operating on the birds’ wintering grounds, breeding grounds or on migration routes, and to identify ways to reverse them.
Many of the morphological features of animals are considered to be adaptations to the habitat that the animals utilize. The habitats utilized by birds vary, perhaps more than for any other group of vertebrates. Here, we study possible adaptations in the morphology of the skeletal elements of the hind limbs to the habitat of birds. Measurements of the lengths of the femur, tibiotarsus and tarsometatarsus of 323 bird species from 74 families are used together with body mass data, taken from the literature. The species are separated into six habitat groups on the basis of literature data on leg use. A discriminant analysis of the groups based on leg morphology shows that swimming birds, wading birds and ground living species are more easily identified than other birds. Furthermore, functional predictions are made for each group based on ecological and mechanical considerations. The groups were tested for deviation from the norm for all birds for three indices of size- and leg-length-independent measures of the bones and for a size-independent-index of leg length. Several of the groups deviate significantly from the norm for one or more of the indices used, suggesting habitat-related adaptations in the leg morphology of birds. The results indicate that stability is an important factor affecting the leg morphology of primarily long-legged birds. The femur seems to be more important than previously thought because several of the groups have high femur indices, suggesting a positive selection pressure on this bone. On a general basis, the results suggest that the effect of leg length should be taken into consideration when discussing adaptations of mass-independent lengths of the long bones of the legs of birds. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 461–484.
There are many sources of natural selection that can favour the evolution of ecological specialization in diet, habitat use or physiological tolerance. This review includes discussion of the ecological bases of such an evolution: environmental constancy, foraging theory, interspecific interactions, and mating rendezvous. Trade-offs and constraints are noted, and macroevolutionary aspects are outlined. Clades may be distinguished in which a particular specialization is phylogenetically conservative; in other clades species have different specializations. In the former case, trade-offs in morphological and physiological traits may enforce commitment to a historically acquired particular specialization; in the latter, selection for specialization per se may be imposed by ecological factors, eg competition or mating success. -P.J.Jarvis
Examined the expected relationship between the ubiquity of species in samples and the realized edaphic habitat volumes of these species. The habitat space of a suite of plants from southern Western Australia was defined by principal-components analysis of soil data. The habitat volumes of 36 scarce and 41 ubiquitous species were not significantly different. An alternative hypothesis is suggested, that scarce plants do not have restricted environmental tolerances but, rather, fill their habitat space more sparsely. Strong correlations between species frequencies in samples and habitat volume were observed in the total data set and in 8 of 10 plant guilds, corroborating predictions, but only half the correlations within guilds were significant at the 5% level when statistical bias from sampling frequency was taken into account. -from Author
Ecology Letters (2010) 13: 267–283
Predicting changes in community composition and ecosystem function in a rapidly changing world is a major research challenge in ecology. Traits-based approaches have elicited much recent interest, yet individual studies are not advancing a more general, predictive ecology. Significant progress will be facilitated by adopting a coherent theoretical framework comprised of three elements: an underlying trait distribution, a performance filter defining the fitness of traits in different environments, and a dynamic projection of the performance filter along some environmental gradient. This framework allows changes in the trait distribution and associated modifications to community composition or ecosystem function to be predicted across time or space. The structure and dynamics of the performance filter specify two key criteria by which we judge appropriate quantitative methods for testing traits-based hypotheses. Bayesian multilevel models, dynamical systems models and hybrid approaches meet both these criteria and have the potential to meaningfully advance traits-based ecology.
Despite increasing interest in urban ecology the factors limiting the colonisation of towns and cities by species from rural areas are poorly understood. This is largely due to the lack of a detailed conceptual framework for this urbanisation process, and of sufficient case studies. Here, we develop such a framework. This draws upon a wide range of ecological and evolutionary theory and the increasing number of studies of how the markedly divergent conditions in urban and rural areas influence the traits of urban populations and the structure of urban assemblages. We illustrate the importance of this framework by compiling a detailed case study of spatial and temporal variation in the urbanisation of the blackbird Turdus merula. Our framework identifies three separate stages in the urbanisation process: (i) arrival, (ii) adjustment, and (iii) spread. The rate of progress through each stage is influenced by environmental factors, especially human attitudes and socio-economic factors that determine the history of urban development and the quality of urban habitats, and by species' ecological and life-history traits. Some traits can positively influence progression through one stage, but delay progression through another. Rigorous assessment of the factors influencing urbanisation should thus ideally pay attention to the different stages. Urbanisation has some similarities to invasion of exotic species, but the two clearly differ. Invasion concerns geographic range expansion that is external to the species' original geographic range, whilst urbanisation typically relates to filling gaps within a species' original range. This process is exemplified by the blackbird which is now one of the commonest urban bird species throughout its Western Palearctic range. This is in stark contrast to the situation 150 years ago when the species was principally confined to forest. Blackbird urbanisation was first recorded in Germany in 1820, yet some European cities still lack urban blackbirds. This is especially so in the east, where urbanisation has spread more slowly than in the west. The timing of blackbird urbanisation exhibits a marked spatial pattern, with latitude and longitude explaining 76% of the variation. This strong spatial pattern contrasts with the weaker spatial pattern in timing of urbanisation exhibited by the woodpigeon Columba palumbus (with location explaining 39% of the variation), and with the very weak spatial pattern in timing of black-billed magpie Pica pica urbanisation (in which location explains 12% of the variation). Strong spatial patterns in timing of urbanisation are more compatible with the leap-frog urbanisation model, in which urban adapted or imprinted birds colonise other towns and cities, than with the independent urbanisation model, in which urban colonisation events occur independently of each other. Spatial patterns in isolation do not, however, confirm one particular model. Factors relating to the arrival and adjustment stages appear particularly likely to have influenced the timing of blackbird urbanisation. Spatial variation in the occurrence of urban populations and the timing of their establishment creates opportunities to assess the factors regulating urbanisation rates, and how the composition of urban assemblages develops as a result. These are major issues for urban ecology.