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Spatial and Temporal Variation in Costa Rican Fruit and Fruit-Eating Bird Abundance
Ecological Monographs
Abstract and Figures
Understory fruit and fruit-eating birds were censused monthly for a year in gaps, intact forest, and second-growth sites of a lowland Costa Rican rain forest. Both fruits and birds displayed significant seasonal variation. Peak fruit abundance corresponded with peak fruit-eating bird abundance. Fruits were most abundant in the mid-to-late rainy season (August-January). Crop sizes were larger on second-growth plants than on either gap or intact forest plants. Also, fruit was much more common in second growth than in gaps and more common in gaps than in intact forest. Fruit-eating birds followed the same general patterns of spatial and temporal variation. They were significantly most abundant in second growth, significantly least abundant in intact forest, and most common from October to January. A large increase in the frugivore population in October was due to an influx of temperate and altitudinal migrants. In addition, populations of some resident frugivore species increased concurrently, suggesting altitudinal migration in some of these species as well. The two most common understory frugivores molted during the period of fruit high and bred during the period of fruit low. I suggest that insect abundance may be more important than fruit abundance in determining breeding cycles of these birds. Given the extent of spatial and temporal variation in fruit and frugivore abundance, and the apparent tracking of fruit resources by birds, large areas of diverse habitats are probably necessary for the long-term maintenance of frugivore populations.
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... The greatest bird diversity was observed in the natural forest type habitat all year-round, but peaking during the wet season when fruits and insects are expected to be the most abundant. Overall, the natural forest is believed to provide more resources such as insects, rodents, and seeds or fruits to birds (Levey 1988;Williams and Middleton 2008), together with nesting sites, wintering sites for migratory birds, and thermal refugia (Stratford and Şekercioğlu 2015). Another important factor likely explaining the higher diversity of birds in the natural forest is the fact that this is the most extensive habitat in the area, with a correspondingly higher capacity for resource provisioning (Dwyer 1972;Wu et al. 2011;Cintra and Naka 2012;Morelli et al. 2017). ...
... Such seasonal variation is likely associated with patterns of seasonality in the food supply, habitat quality and breeding behaviour of the species (Ayinalem and Bekele 2008;Ganjeh et al. 2017;Girma et al. 2017). In general, spatio-temporal patterns of bird species distribution and abundance are determined by abundance and the seasonal availability of food (Levey 1988) as well as climate variability, particularly rainfall, which is strongly associated with food availability (Williams and Middleton 2008). Levey (1988) states that edible fruits are most abundant during the mid-to-late rainy season, and crop sizes are more extensive in the late rainy season, which aligns with findings of the present study that showed an increase in the numbers of individuals in the natural forest and farmland habitats during the wet and dry seasons, respectively. ...
... In general, spatio-temporal patterns of bird species distribution and abundance are determined by abundance and the seasonal availability of food (Levey 1988) as well as climate variability, particularly rainfall, which is strongly associated with food availability (Williams and Middleton 2008). Levey (1988) states that edible fruits are most abundant during the mid-to-late rainy season, and crop sizes are more extensive in the late rainy season, which aligns with findings of the present study that showed an increase in the numbers of individuals in the natural forest and farmland habitats during the wet and dry seasons, respectively. ...
... (a) Reconciling positive and negative density-dependent frugivory At first, the widespread occurrence of NDD frugivory may seem paradoxical because what has been amply documented is the opposite. Studies show that fruit abundance is a strong predictor of frugivore activity in habitats and landscapes [38][39][40]. ...
Negative density dependence (NDD) in biotic interactions of interference such as plant–plant competition, granivory and herbivory are well-documented mechanisms that promote species’ coexistence in diverse plant communities worldwide. Here, we investigated the generality of a novel type of NDD mechanism that operates through the mutualistic interactions of frugivory and seed dispersal among fruit-eating birds and plants. By sampling community-wide frugivory interactions at high spatial and temporal resolution in Pennsylvania, Puerto Rico, Peru, Brazil and Argentina, we evaluated whether interaction frequencies between birds and fruit resources occurred more often (selection), as expected, or below expectations (under-utilization) set by the relative fruit abundance of the fruit resources of each plant species. Our models considered the influence of temporal scales of fruit availability and bird phylogeny and diets, revealing that NDD characterizes frugivory across communities. Irrespective of taxa or dietary guild, birds tended to select fruits of plant species that were proportionally rare in their communities, or that became rare following phenological fluctuations, while they mostly under-utilized abundant fruit resources. Our results demonstrate that negative density-dependence in frugivore–plant interactions provides a strong equalizing mechanism for the dispersal processes of fleshy-fruited plant species in temperate and tropical communities, likely contributing to building and sustaining plant diversity.
This article is part of the theme issue 'Diversitydependence of dispersal: interspecific interactions determine spatial dynamics'.
... Percentage ripe fruit abundance was measured during the early (November-December), mid (January-February), and late ( Successional stage also influences local abiotic conditions, especially light availability. The increased flower and fruit abundance we observed on more recently disturbed transects has been found in younger seres elsewhere (Blake & Loiselle, 1991;Levey, 1988;Martin, 1985). Second growth species reproduce over longer periods and produce larger fruit crops relative to species that grow in the shaded understory of mature forests (Denslow et al., 1986;Opler et al., 1980). ...
The reproductive phenology of plants has profound influence on ecosystem dynamics including plant–animal interactions. Broad phenological patterns, especially the timing of reproduction, may result from long-term climate trends and co-evolution between plants and their pollinators, dispersers, and predators. Yet, interannual climate variation and local abiotic conditions may also affect the timing and magnitude of plant reproduction. Understanding the patterns of and controls on plant reproduction are crucial for conservation efforts under a changing global climate and rapidly expanding human development. However, phenology studies from the Neotropics are sparse. Here, we examine the relative timing and magnitude of fleshy-fruited plant reproduction during the winter dry season in subtropical dry forest on Eleuthera, The Bahamas over a nine-year period. At least 47 species were observed with some dry season reproductive activity, but only 17% showed evidence of a fruiting peak or continuous reproduction. Overall fruit abundance generally declined through the dry season, but flower production increased between mid and late dry season. Variation in fruit and flower abundance among years was related to temperature and rainfall, but local site conditions—particularly stage and groundwater availability—explained more variability in reproductive activity than climate variation. Groundwater availability had a particularly strong positive influence on flower and fruit abundance at the end of the dry season, a critical time for migrant frugivores preparing to return to their breeding grounds. This emphasizes the importance of protecting sites with accessible groundwater to conserve biodiversity in the archipelago and elsewhere.
... Even in climatically harsh boreal and tundra biomes, some plants retain fruits into the autumn and winter (Mulder et al., 2021), representing a crucial resource of frugivores outside of the growing season. Shifting availability of floral and fruit resources can also have strong effects on the spatial and temporal distribution of pollinators and frugivorous seed-disperser populations (Levey, 1988a;Levey, 1988b;Kinnaird et al., 1996;Olesen et al., 2011). Over the past 30 years, a rapidly growing literature on the structure and function of bipartite plant-mutualist networks has developed (Jordano, 1987;Bascompte and Jordano, 2013;Valdovinos, 2019;Valdovinos and III, 2021), yet it has remained largely distinct from classic food web studies. ...
Recent theoretical work has provided major new insights into the ways that species interactions in food webs are organized in ways that permit the coexistence of significant numbers of species. But, we seem to have forgotten about trees! Not the phylogenetic ones that are increasingly important for dissecting the evolutionary structure of food webs, but the trees, shrubs and grasses that are the basal species in all terrestrial ecosystems. Many of the food webs available for analysis over the last 30 years were based on freshwater or marine systems where algae were the main plants. Trees are very different from algae; they can live for centuries, while annually producing leaves, fruits and seeds that provide nutrients for a diversity of species on higher trophic levels. In sharp contrast to algae, they are only partly consumed by herbivores and usually compensate or recover from herbivory. Most of the biomass in terrestrial systems is in the plants, this again contrasts with aquatic systems, where most of the biomass is in primary and secondary consumers. Moreover, each individual tree supports its own food web of species that are only partially coupled to those of surrounding trees. If we are going to apply our theoretical understanding of food-web structure to species-rich terrestrial ecosystems in ways that are insightful for conservation, then we need a deeper examination of the role that higher plants play in food webs. While community ecology has developed an increasingly detailed understanding of the ways plant communities are organized, this seems to have evolved almost independently of the food-web literature. In this article, we make a plea to more sharply consider higher plants in food webs and to do this by combining recent theoretical work on food webs, with recent empirical and theoretical work on plant communities. Ultimately, we argue for a deeper integration of plant community ecology into studies of food webs.
... Frugivores are concentrated in the few trees where they can find their preferred fruit (e.g. Levey 1988, Herrera 1998, Jordano 2015 and nectarivores select nectar-producing flowering trees (e.g. Feinsinger 1976, Pettet 1977, Symes et al. 2008. ...
The Sahel is thinly covered by trees, but nevertheless forms an important habitat
for millions of tree-dwelling birds. We describe tree availability and tree selection
of 14 insectivorous Afro-Palearctic migrants and 18 Afro-tropical residents (10
insectivores, 3 frugivores and 5 nectarivores) inhabiting the Sahel from the
Atlantic to the Red Sea. Of the 304 woody species identified across the region
during systematic fieldwork in stratified plots, we noted height and canopy
surface of 760,000 individual woody plants. Birds present in trees and shrubs
were recorded separately per individual woody plant. 99.5% of the birds were
concentrated in only 41 woody species. For 20 out of 32 bird species, Winter
Thorn Faidherbia albida was the tree species most often used. Two other important
tree species were Umbrella Thorn Acacia tortilis and Desert Date Balanites
aegyptiaca. Representing only 11% of the total woody canopy cover, these three
species attracted 89% of Western Bonelli’s Warblers Phylloscopus bonelli and
77% of Subalpine Warblers Curruca iberiae + subalpina + cantillans. High selectivity
for particular woody species was typical for migrants and residents, irrespective
of their diet. Bird species feeding in shrubs used a larger variety of
woody species than bird species feeding in tall trees. The highest bird densities
(80–160 birds/ha canopy) were found in three shrubs with a limited distribution
in the southern Sahara and northern Sahel: the berry-bearing Toothbrush Tree
Salvadora persica, the small thorny shrub Sodad Capparis decidua and the
small tree Maerua crassifolia. Other bird-rich woody species were without
exception thorny (Balanites aegyptiaca, various species of acacia and ziziphus).
In contrast, the five woody species most commonly distributed across the region
(Cashew Anacardium occidentale, African Birch Anogeissus leiocarpus, Com -
bretum glutinosum, Guiera senegalensis and Shea Tree Vitellaria paradoxa),
representing 27% of the woody cover in the study sites, were rarely visited by
foraging birds. In this sub-Saharan region, it is not total woody cover per se that
matters to birds, but the presence of specific woody species. This finding has
important implications: remote sensing studies showing global increase or
decline of woody vegetation without identifying individual species have little
value in explaining trends in arboreal bird populations. Local people have a large
impact on the species composition of the woody vegetation in the Sahel, with
positive and negative consequences for migrants wintering in this region.
Faidherbia albida, the most important tree for birds in the sub-Saharan dry belt,
is highly valued by local people and has the distinction of leafing in winter and
being attractive to arthropods. On the other hand, migratory and African bird
species have been negatively affected by the rapidly expanding cashew plantations
since the early 1980s.
The 62 species of hornbills around the world are extravagant birds with over-sized beaks that are found in tropical Asia, Africa, Indonesia, and Papua New Guinea. They are icons of their forest habitat. Because they spread the seeds of several tropical trees, they are frequently referred to as the "farmers of the forest" because of the way they spread forest tree seeds over the area they fly over. Hornbills regurgitate or vomit the seeds after eating as they typically occupy a home range of at least 10 km, they may disperse seeds across a far larger area with far greater efficiency than other smaller frugivores. They are a sign of a balanced and prosperous forest. For this reason, hornbills are regarded as an indicator species. The tale of how the bond between these birds and the long-standing custom of protecting forests in the name of a deity has helped to preserve both the unprotected forests and sacred groves throughout wide-ranging terrain. In recognition of the significance of these birds, and to ensure the continuity of this unique alliance, conservation initiatives have gained a greater spotlight. Conservation organizations, farmers, and local communities are working together to protect hornbill habitats and spread awareness among the local communities for safeguarding the agricultural landscapes inhabited by them by fostering a greater appreciation of the ecological and cultural worth of hornbills.
Keywords: Hornbills, ‘Farmers of the Forest’, Wide Ranging Terrain, Agricultural Landscapes, Conservation Organizations.
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33. Sericulture
The ecological effect on the functional diversity of migrant birds in Neotropical habitats is poorly understood. So, the aim of this study is to investigate functional diversity differences of resident and migratory bird species. Hence, we assess trait space occupancy differences in resident and migrant bird species across three Mato Grosso do Sul (MS) state habitats. Using the MS bird checklist and literature data, we categorized migratory species into three groups based on their habitat associations: aquatic, forest, and non-forest. We utilized 26 functional traits, grouped into three categories (morphological traits, diet composition, and foraging forest stratum preference), to assess the functional diversity in habitat dependency groups. Calculating functional richness and functional dispersion for each habitat dependency group, along with the functional beta diversity between resident and migratory species, we found that migratory birds add new traits to aquatic groups, showing high functional turnover. Conversely, the forest and non-forest groups showed greater nestedness, indicating greater functional redundancy between migratory and resident species in these habitats. Migratory and resident groups exhibited higher overlap in functional volume in forest and non-forest habitats but show minimal overlap in aquatic habitats. This suggests that the effect of migratory species should be higher in aquatic habitats of MS because they add considerable variation in functional traits, which do not exist in the resident species. In conclusion, our study underscores the importance of preserving MS wetlands, particularly the Pantanal and the upper Paraná River floodplains, for the conservation of aquatic migratory species and their ecological role.
About half of the approximately 10,000 species of birds are classified as migrants. Ideas about the origins of avian migration are discussed in this chapter and, for present-day birds, the distances, routes, and heights that migrants fly are explained. In mountainous regions, many species of birds are altitudinal migrants and the reasons why birds exhibit such behavior are discussed. The reasons why some migrants follow loop and figure-eight migration routes are also explained. Also discussed is the importance of stopover sites for migrants. Other topics covered in this chapter include bird migration in the Neotropics and seasonal differences in the speed of migration. Many migratory species exhibit protandry, with males arriving in breeding areas before females and factors contributing to such behavior are discussed. Reasons why birds migrate during the day versus at night are explained, and the chapter closes with a discussion of the possible effects of climate change on bird migration.
Bird-dispersed plants of the tropical rain forest understory are widely spaced and produce sparse crops (most with fewer than 10 ripe fruits available at any one time). Such plants probably disperse the greatest proportion of their lifetime output of seeds in the short periods during which they occur in treefall gaps. There, environmental conditions stimulate the production of large crops of fruit. At the same time, however, competition for dispersers is also likely to be high because of the proximity of other fruiting plants in the same clearings. For birddispersed shrubs and treelets, treefall clearings thus represent both critical opportunities for fruit production and seed dispersal and effective bottlenecks of increased competitive pressure from other fruiting plants.
A preliminary series of transects, covering approximately the first 200 years of forest development on undisturbed riverbends in Peruvian lowland forest, were analyzed for community changes in plant dispersal spectrum and its apparent consequences. The annual beach community is composed of approximately half true beach species and half seedlings of forest species. The seedlings of those species dominating the canopy for the first few centuries are present at the initial stages of forest development, and the riverbend deposition process is seen as critical for the maintenance of naturally occuring stands of large trees. Water, bats and wind are the principal initial determinants of forest community structure. Both the understory and canopy fill in first with more bird-dispersed and later with more mammal-dispersed species. Some floristic differences between adjacent old river levees are attributable to age and site characteristics, but seed availability and dispersal are probably more important.
Of 44 species represented by adequate sample sizes (n>5) in spring, 9 were significantly more common in gaps, 2 more common in forest understorey. Nine of 17 species were captured more often in gaps during fall. During spring, flycatchers, ground insectivores, foliage insectivores, and granivore-omnivores were captured more frequently in gaps. Flycatchers showed no difference in fall, but other trophic groups, including frugivores, were captured more frequently in gaps than in forest understory sites. Bark foragers showed no statistical preference for gaps or forest understory in spring or fall. Total species per net and total captures per net correlated positively with density of foliage in the lower canopy and negatively with density of upper canopy foliage in both spring and fall. Total species and captures correlated positively with insect abundance in spring and with fruit abundance in fall. Foliage insectivores correlated positively with low canopy foliage and insect abundance in both spring and fall. Captures of frugivores correlated with fruit abundance in fall. Data support the hypothesis that birds are attracted to tree-fall gaps because of higher resource abundance.-from Authors
Studies at Pasoh Forest Reserve (Negri Sembilan, Peninsular Malaysia) established that flowers and fruits were consistently rare as food for birds. Food resources (flowers, fruits, arthropods) were less abundant in regenerating than in virgin forest; bird species richness and individual abundance were also lower in the regenerating forest understory. However, the two forests did not differ significantly in the relative importance of the various foraging guilds, suggesting that similar types of resources were present in similar proportions. None of the birds was a specialized consumer of understory flowers or fruit, whereas birds feeding mainly on foliage-dwelling arthropods were abundant and were represented by many species. This trophic organization is contrary to that reported for rain forests in other tropical regions but may simple reflect an allocation of harvestable productivity that is different rather than lower.-from Author