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Determinants of fine-scale homogenization and differentiation of native freshwater fish faunas in a Mediterranean Basin: Implications for conservation
Diversity and Distributions
Abstract
Aim Increasing threats to freshwater biodiversity are rapidly changing the distinctiveness of regional species pools and local assemblages. Biotic homogenization/differentiation processes are threatening the integrity and persistence of native biodiversity patterns at a range of spatial scales and pose a challenge for effective conservation planning. Here, we evaluate the extent and determinants of fine‐scale alteration in native freshwater fish assemblages among stream reaches throughout a large river basin and consider the implications of these changes for the long‐term conservation of native fishes.
Location Guadiana River basin (South‐Western Iberian Peninsula).
Methods We quantified the magnitude of change in compositional similarity between observed and reference assemblages and its potential effect on natural patterns of compositional distinctiveness. Reference assemblages were defined as the native species expected to occur naturally (in absence of anthropogenic alterations) and were reconstructed using a multivariate adaptive regression splines predictive model. We also evaluated the role of habitat degradation and introduced species as determinants of biotic homogenization/differentiation.
Results We found a significant trend towards homogenization for native fish assemblages. Changes in native fish distributions led to the loss of distinctiveness patterns along natural environmental gradients. Introduced species were the most important factor explaining the homogenization process. Homogenization of native assemblages was stronger in areas close to reservoirs and in lowland reaches where introduced species were more abundant.
Main conclusions The implementation of efficient conservation for the maintenance of native fish diversity is seriously threatened by the homogenization processes. The identification of priority areas for conservation is hindered by the fact that the most diverse communities are vanishing, which would require the selection of broader areas to adequately protect all the species. Given the principal role that introduced species play in the homogenization process and their relation with reservoirs, special attention must be paid to mitigating or preventing these threats.
... Nonnative species have been shown to be strongly associated with land use alteration and flow regime changes (Gido et al., 2004;Marchetti et al., 2006;Leprieur et al., 2008), and artificially constructed reservoirs appear to be particularly favorable to their life history strategies (Gido et al., 2009;Pool et al., 2010). But despite evidence that reservoirs homogenize freshwater assemblages (Clavero & Hermoso, 2011;Hermoso et al., 2012), the extent to which the homogenizing effects of reservoirs extend into adjacent running water ecosystems is relatively unknown. For example, range expansions of nonnative species out of reservoir environments resulting from climate change could lead to further homogenization between stream and reservoir assemblages (Buisson & Grenouillet, 2009;Clavero & Hermoso, 2011;Bae et al., 2018). ...
... Studies investigating biotic homogenization have focused primarily on large scales (e.g., increased similarity of fish faunas among basins, watersheds, or ecoregions), and there is a lack of comparative studies on how the processes of homogenization and differentiation vary between large and small scales (e.g., local site scales; Lambdon et al., 2008;Hermoso et al., 2012). Differentiation is the process opposite of homogenization, whereby assemblages become less similar in their faunal compositions (Olden & LeRoy Poff, 2003;Rahel, 2010). ...
... We statistically tested for changes in pairwise faunal similarities between contemporary and historical periods for each spatial scale using a test for homogeneity of multivariate dispersion (betadisper function; R v. 3.4.2), which is frequently used for evaluating statistical differences in similarity metrics (Olden et al., 2008;Hermoso et al., 2012). Multivariate dispersion calculates the mean distance of points to the group centroid in multivariate space with decreasing distances to the centroid representing tighter spatial clustering and thus indicative of homogenization. ...
Reservoir construction and the introduction of nonnative species are major anthropogenic drivers of biotic change in freshwater ecosystems. To understand the influence of these drivers, we quantified the degree to which fish faunas have either homogenized or differentiated at multiple spatial scales across the Great Plains—Rocky Mountain continuum (Wyoming, USA), given that homogenization processes are scale-dependent. Homogenization was most prevalent at the largest scale, with an average increase in similarity of 6.8% among river basins. At an intermediate scale, sub-basins with reservoirs had homogenized faunas in comparison to sub-basins without reservoirs, which were more differentiated. Differentiation was dominant at the smallest scale with a 7.8% average decrease in similarity among individual sampling sites. Reservoirs had only localized homogenization impacts along stream systems, and homogenization was greater for streams connected to large reservoirs. Large-sized streams appeared to trend towards homogenization, whereas small and medium streams trended towards differentiation. Reservoirs altered fish faunas from historical conditions, but did not result in cross-stream homogenization because of the idiosyncratic nature of reservoir introductions that reflect environmental gradients and socio-economic factors. Our results provide insight into how spatial scale, reservoirs, and nonnative species interact to influence the degree of homogenization and differentiation.
... For instance, the taxonomic similarity between the world's freshwater fish faunas in river basins has increased on average by 0.5% over the past two centuries (Vill eger et al., 2011). This overall trend towards regional and global taxonomic homogenization is nevertheless contrasted for several taxa, with some assemblages' pairs showing taxonomic differentiation (Shaw et al., 2010;Vill eger et al., 2011;Hermoso et al., 2012). ...
... Indeed, the industrial revolution of the 19th century was the starting point of a steep increase of human impacts on natural ecosystems (Butchart et al., 2010;Ellis et al., 2010) and of the development of a massive intercontinental trade responsible for most non-native species introductions (Taylor & Irwin, 2004;Vander Zanden, 2005;Leprieur et al., 2008a;Blanchet et al., 2009). Although the patterns and determinants of changes in taxonomic similarity between assemblages from historical to current situation have been increasingly studied (Rahel, 2000;Olden & Poff, 2004;Leprieur et al., 2008b;Spear & Chown, 2008;Winter et al., 2009;Vill eger et al., 2011;Hermoso et al., 2012), much less attention has been devoted to future trends (but see Duncan & Lockwood, 2001;Olden & Poff, 2004;Olden et al., 2008a;Matsuzaki et al., 2013), especially at large spatial scales. Yet, both native species extirpations and non-native species introductions are supposed to increase in the next decades under accelerated rates of climate change, resource exploitation, habitat change and global trade (Sala et al., 2000;Hulme et al., 2009;Clavero, 2011). ...
... non-native species introductions not dependent on native species richness) and a frequencydependent probability of introduction appear the most probable scenarios for most river basins. Indeed, previous studies have found that, at the river basin scale, the nonnative species richness is mainly driven by human activities, whereas biotic acceptance or biotic resistance has weak effects (Leprieur et al., 2008a;Blanchet et al., 2009;Hermoso et al., 2012). Furthermore, the non-native species already established in numerous river basins will have the highest probability to increase their number of occurrences in the near future through natural expansion of their distribution range (Kolar & Lodge, 2001;Olden et al., 2006b;Britton et al., 2011). ...
AimAssessing the consequences of a future increase in non-native species introductions and native species extirpations on taxonomic similarity among fish faunas.LocationWorld-wide.Methods
We designed 42 scenarios of future species introductions and extirpations to simulate future fish composition for 1054 river basins. Using these simulated future compositions, we computed the change in taxonomic similarity among pairs of fish faunas from historical to future situation at the river basin, biogeographic realm and world scales.ResultsAccording to all our scenarios, taxonomic similarity among fish faunas will strongly increase in the future at the three spatial scales considered. Fish faunas from the Southern Hemisphere, which are currently the less affected by taxonomic homogenization, are forecasted to show the steepest changes. Our scenarios also reveal that non-native species introductions will account for most of the predicted changes, whereas the effect of native species extirpations will be weak.Main conclusionsThe predicted future taxonomic homogenization will blur the current high level of taxonomic dissimilarity among freshwater fish faunas, and therefore, imperil the conservation programmes based on beta-diversity mapping.
... Owing to past isolation, high variation in flow regimes, and frequent droughts, freshwater fish communities in mediterranean climates are usually depauperate, but often with a high proportion of endemic 123 species (Swift et al., 1993;Bianco, 1995;Economidis, 1995;Vila-Gispert et al., 2002;Lin & Ambrose, 2005;Marchetti et al., 2006;Ferreira et al., 2007;Impson, 2007;Zogaris et al., 2009;Clavero et al., 2010;Marr et al., 2010). Fish species richness in these regions has been considerably augmented by the introduction or invasion of exotic species, often associated with reservoirs and altered flow regimes (Bianco, 1995(Bianco, , 1998Economidis et al., 2000;Corbacho & Sánchez, 2001;Elvira & Almodóvar, 2001;Marchetti et al., 2004;Innal & Erk'akan, 2006;Kara, 2011;Hermoso et al., 2012). Most, but not all, studies in southern California have reported a positive relationship between the number of exotic fish species and urbanization ( Fig. 3c; Brown et al., 2005b;Lin & Ambrose, 2005;Riley et al., 2005). ...
... Clavero et al. (2010) reported that exotic species and waterscape alterations (primarily water extraction) were the dominant threats to endemic species in the Iberian Peninsula, central Italy, and parts of northwestern Turkey, but that agricultural activity and pollution were the major threats to endemic species in the southern Balkan Peninsula and along the Mediterranean eastern rim. Analyses at regional or basin scales suggest that exotic species have had negative effects on native species (Light & Marchetti, 2007;Hermoso et al., , 2012. Other researchers have argued that evidence for the magnitudes and mechanisms of exotic fish species impacts on native species is largely circumstantial and inconclusive (Ribeiro & Leunda, 2012). ...
... In the Western Cape Province of South Africa, the introduction of exotic fish species, particularly piscivorous species like the smallmouth bass (Micropterus dolomieu Lacepede), has resulted in the decline and sometimes local extirpation of native fish species (Clark et al., 2009;Lowe et al., 2010;Woodford et al., 2010). Although fish faunas in the med-regions of the world were originally distinctive, there is increasing homogenization as native species dwindle and introduced species become widespread and dominant (Clavero & García-Berthou, 2006;Marr et al., 2010;Hermoso et al., 2012). ...
We reviewed the literature on the effects of land use changes on mediterranean river ecosystems (med-rivers) to provide a foundation and directions for future research on catchment management during times of rapid human population growth and climate change. Seasonal human demand for water in mediterranean climate regions (med-regions) is high, leading to intense competition for water with riverine communities often containing many endemic species. The responses of river communities to human alterations of land use, vegetation, hydrological, and hydrochemical conditions are similar in mediterranean and other climatic regions. High variation in hydrological regimes in med-regions, however, tends to exacerbate the magnitude of these responses. For example, land use changes promote longer dry season flows, concentrating contaminants, allowing the accumulation of detritus, algae, and plants, and fostering higher temperatures and lower dissolved oxygen levels, all of which may extirpate sensitive native species. Exotic species often thrive in med-rivers altered by human activity, further homogenizing river communities worldwide. We recommend that future research rigorously evaluate the effects of management and restoration practices on river ecosystems, delineate the cause–effect pathways leading from human perturbations to stream biological communities, and incorporate analyses of the effects of scale, land use heterogeneity, and high temporal hydrological variability on stream communities.
... urban development, water diversion and stream flow modification for agriculture; Marchetti et al., 2004;Kennard et al., 2005;Light and Marchetti, 2007;Hermoso et al., 2011). Non-natives can also modify the homogenisation or heterogenisation effect of land use on biodiversity at regional scales (Olden and Poff, 2003;Marchetti et al., 2006;Hermoso et al., 2012). However, the scale dependent effect of non-natives on the biodiversity of native communities in different land use types remains largely unknown (e.g. ...
... We predicted that differences in land use would induce changes in the environmental characteristics of streams, which would subsequently lead to differences in the diversity and structure of fish communities. We expected that both the alpha and beta diversity of native fishes would be highest in protected, relatively natural sites, intermediate in agricultural sites, and lowest in urban sites (Kennard et al., 2005;Scott, 2006;Trautwein et al., 2012), due to increasing perturbation effects and, consequently, homogenisation of habitat structure (Scott, 2006;Hermoso et al., 2012). We also expected that natural stream conditions would make the habitat more resistant to invasion (Marchetti and Moyle, 2001), and that protected status would ensure the preservation of natural stream habitats to some degree. ...
Increasing agriculture and urbanization inevitably lead to changes in the biodiversity of stream ecosystems. However, few studies examined comprehensively how biodiversity is distributed within and among protected, agricultural and urban land use types in streams. We studied environmental characteristics of streams and patterns of species richness and other community attributes of stream fish communities in these three characteristic land use types in the catchment of the Danube River, Hungary. Land use separated streams to some degree based on their environmental characteristics. However, both between stream environmental and fish community variability were high in most types, and comparable to land use type level differences in case of many streams. A variety of environmental gradients influenced fish community structure rather independently of land use type, which was also influenced by spatial drivers. Non-native fishes modified the structure of native fish communities, especially in agricultural streams, although their modification effect varied more among individual streams than among land use types. In conclusion, land use type proved to be a poor predictor of fish communities in this human modified landscape. We found that even intensively managed areas (i.e. agricultural and urban) can contribute to the maintenance of fish diversity in this biogeographic region, or at least their potential can be comparable to those streams which flow in protected areas. Thus, conservation management should focus on maintaining streams in more natural condition in protected areas and/or use the potential of non-protected agricultural and urban streams in maintaining fish diversity in human modified landscapes.
... urban development, water diversion and stream flow modification for agriculture; Marchetti et al., 2004;Kennard et al., 2005;Light and Marchetti, 2007;Hermoso et al., 2011). Non-natives can also modify the homogenisation or heterogenisation effect of land use on biodiversity at regional scales (Olden and Poff, 2003;Marchetti et al., 2006;Hermoso et al., 2012). However, the scale dependent effect of non-natives on the biodiversity of native communities in different land use types remains largely unknown (e.g. ...
... We predicted that differences in land use would induce changes in the environmental characteristics of streams, which would subsequently lead to differences in the diversity and structure of fish communities. We expected that both the alpha and beta diversity of native fishes would be highest in protected, relatively natural sites, intermediate in agricultural sites, and lowest in urban sites (Kennard et al., 2005;Scott, 2006;Trautwein et al., 2012), due to increasing perturbation effects and, consequently, homogenisation of habitat structure (Scott, 2006;Hermoso et al., 2012). We also expected that natural stream conditions would make the habitat more resistant to invasion (Marchetti and Moyle, 2001), and that protected status would ensure the preservation of natural stream habitats to some degree. ...
Increasing agriculture and urbanization inevitably lead to changes in the biodiversity of stream ecosystems. However, few studies examined comprehensively how biodiversity is distributed within and among protected, agricultural and urban land use types in streams. We studied environmental characteristics of streams and patterns of species richness and other community attributes of stream fish communities in these three characteristic land use types in the catchment of the Danube River, Hungary. Land use separated streams to some degree based on their environmental characteristics. However, both between stream environmental and fish community variability were high in most types, and comparable to land use type level differences in case of many streams. A variety of environmental gradients influenced fish community structure rather independently of land use type, which was also influenced by spatial drivers. Non-native fishes modified the structure of native fish communities, especially in agricultural streams, although their modification effect varied more among individual streams than among land use types. In conclusion, land use type proved to be a poor predictor of fish communities in this human modified landscape. We found that even intensively managed areas (i.e. agricultural and urban) can contribute to the maintenance of fish diversity in this biogeographic region, or at least their potential can be comparable to those streams which flow in protected areas. Thus, conservation management should focus on maintaining streams in more natural condition in protected areas and/or use the potential of non-protected agricultural and urban streams in maintaining fish diversity in human modified landscapes.
... Freshwater fish species are recognizably among the most threatened taxa worldwide, facing an increasingly risk of local, regional, or global extinction mostly due to habitat loss and degradation, invasive species proliferation, pollution, over-exploitation, and direct and indirect effects of climate change (Jenkins 2003, Xenopoulos et al. 2005, Arthington et al. 2016). In the Mediterranean Basin, one of the main hotspots for freshwater biodiversity at a global scale, holding over 200 Key Biodiversity Areas (Máiz-Tomé et al. 2017), the main drivers of native fish declines are water extraction, pollution, and invasive species proliferation (Clavero et al. 2010, Hermoso and Clavero 2011, Hermoso et al. 2012, Gozlan 2012. The Iberian Peninsula is not an exception to this scenario, with about 68% of its native cyprinid ichthyofauna imperilled due to similar threats (Sousa-Santos et al. 2016). ...
... The Iberian Peninsula is not an exception to this scenario, with about 68% of its native cyprinid ichthyofauna imperilled due to similar threats (Sousa-Santos et al. 2016). In particular, the spread and establishment of introduced species poses a strong threat to the conservation of native fishes in highly fluctuating environments and with human-induced disturbances such as the temporary streams of southern Iberia (Hermoso et al. 2012, Ilhéu et al. 2014. ...
Background. Freshwater fishes are among the most threatened taxa worldwide. The proliferation of introduced species in the Iberian Peninsula is currently one of the main drivers of native fish declines. One of such species, the bleak, Alburnus alburnus (Linnaeus, 1758), has become widespread in the last 25 years and, due to its phylogenetic proximity, poses a high risk of hybridization with native species. The aim of this study was to improve the current knowledge on this issue by 1) evaluating the presence of hybrids with Alburnus alburnus in the wild, using molecular screening of individuals representing the intermediate morphology and 2) testing if artificial crosses between Alburnus alburnus and the highly threatened native cyprinid Anaecypris hispanica (Steindachner, 1866) resulted in viable hybrid offspring. Material and methods. The genetic profile of Alburnus alburnus was established using the cytochrome b and beta-actin genes to allow comparisons with the profiles of the sympatric species with which it could potentially hybridize: Anaecypris hispanica; Squalius alburnoides (Steindachner, 1866); and Squalius pyrenaicus (Günther, 1868). This profile was further used to assess if fish with the intermediate morphological features were indeed hybrids. Finally, artificial crosses between Alburnus alburnus and Anaecypris hispanica were conducted to test the viability of the offspring. Results. Alburnus alburnus individuals were genetically identical to the stocks introduced in Spain and the Czech Republic. A reference library composed of 15 species-specific nDNA loci was built and used to characterize wild fish showing intermediate morphological features. Results showed that Alburnus alburnus is currently hybridizing with males and females of Squalius alburnoides and that morphometric identification is insufficient for a reliable detection of the hybrids. Artificial crosses between the bleak and the highly threatened Anaecypris hispanica did not result in viable offspring. Conclusion. Phylogenetic relatedness, traduced in the absence of pre-and post-zygotic barriers to reproduction, together with other factors related to the ecology and life history of the species involved are essential for hybridization to occur. As such, the proliferation of the bleak through the Iberian hydrographical network represents a serious additional threat for the already imperilled native Squalius and Anaecypris species.
... In such impaired contexts, the alteration of species distribution (Parmesan 2006), loss of endangered species ) and the increase in occurrence and abundance of allochthonous invasive species is expected (Fenoglio et al. 2010, Hermoso et al. 2012. ...
This study aims at investigating the environmental factors that drive the presence and proliferation of the invasive diatom Achnanthidium delmontii in some Mediterranean rivers of Liguria (NW-Italy). Achnanthidium delmontii was detected for the first time in Italy in 2013 and has rapidly spread throughout Liguria since then, becoming the dominant taxon in several sites. In this
paper, we analysed chemical data and hydromorphological features to define the ecological preferences of this species. Through a statistical model we showed that the presence of A. delmontii was strongly influenced by its occurrence in upper sections of the watershed or previous sampling campaigns; once established in a certain site the species remains. Moreover, its abundance was significantly related to high percentage of agricultural surrounding land use, alkaline pH and medium-high water temperatures. For the first time, we also observed that the abundance of A. delmontii is positively correlated with hydrological disturbance. Indeed, extreme water scarcity events during summer, the presence of dams along the watercourse, and significant water abstractions, are positively correlated with its proliferation. Conversely, the presence of A. delmontii seems to be negatively affected by hydropeaking events. Our results proved that the conservation of a good habitat integrity and heterogeneity, coupled with the maintenance of a natural flow, represent important defence strategies against the establishment and proliferation of this invasive diatom.
... On the other hand, eDNA metabarcoding sampling in the reservoir showed fewer species, however S. trutta and A. melas were detected that had not been detected in the river by electrofishing, both used for fishing purposes. Likewise, the discrepancies in the composition of fishes between the reservoir and the river to which it flows have been sufficiently demonstrated for other places in the Iberian Peninsula [94,95]. ...
Environmental DNA (eDNA) metabarcoding has been increasingly used to monitor the community assemblages of a wide variety of organisms. Here, we test the efficacy of eDNA metabarcoding to assess the composition of Iberian freshwater fishes, one of the most endangered groups of vertebrates in Spain. For this purpose, we sampled 12 sampling sites throughout one of Spain’s largest basins, the Duero, which is home to approximately 70% of the genera and 30% of the primary freshwater fish in Spain. We sampled these sampling sites in the summer by using electrofishing, a traditional sampling method, and eDNA metabarcoding of river water samples using the mitochondrial 12S rRNA gene ( 12S ) as a marker. We also resampled four of these sampling sites in autumn by eDNA. We compared the results obtained through eDNA metabarcoding with those of electrofishing surveys (ones conducted for the present study and past ones) and assessed the suitability of 12S as an eDNA metabarcoding marker for this group of freshwater fishes. We found that the 12S fragment, analysed for 25 Iberian species, showed sufficient taxonomic resolution to be useful for eDNA approaches, and even showed population-level differences in the studied populations across the tissue samples for Achondrostoma arcasii . In most cases, a greater number of species was detected through eDNA metabarcoding than through electrofishing. Based on our results, eDNA metabarcoding is a powerful tool to study the freshwater fish composition in the Iberian Peninsula and to unmask cryptic diversity. However, we highlight the need to generate a local genetic database for 12S gene for such studies and to interpret the results with caution when studying only mitochondrial DNA. Finally, our survey shows that the high detection sensitivity of eDNA metabarcoding and the non-invasiveness of this method allows it to act as a detection system for species of low abundance, such as early invasive species or species in population decline, two key aspects of conservation management of Spanish freshwater fishes.
... Os resultados de diversidade β evidenciam que a heterogeneidade de substratos é importante para manter a riqueza de espécies de macroinvertebrados, e o componente principal da diversidade β entre os riachos e os substratos foi a substituição de espécies. Ou seja, a cada novo sítio amostrado, as variações são causadas pelo encontro de novas espécies, reforçando a importância de conservar o conjunto de riachos e evitar a homogeneização dos hábitats para manter a diversidade taxonômica de organismos (Hermoso et al., 2012) nos riachos de cabeceira do PARNA Serra do Gandarela e seu entorno. ...
Durante uma disciplina de pós-graduação, realizamos
uma Avaliação Ecológica Rápida sobre qualidade de água e
biodiversidade de bioindicadores bentônicos no Parque Nacional
(PARNA) da Serra do Gandarela, MG. Os objetivos foram: (a)
capacitar profissionais na utilização de metodologias atuais em
Rapid Assessment Protocols (RAP) para estudos de diagnóstico
e monitoramento de integridade ecológica de ecossistemas
aquáticos em regiões de cabeceira de bacias hidrográficas; (b)
contribuir ao conhecimento da biodiversidade aquática em corpos
d’água no PARNA Serra do Gandarela; (c) fomentar intercâmbio
e colaboração entre mestrandos, doutorandos, guarda-parques,
visitantes, membros de comitês de bacia, gestores ICMBio,
moradores e interessados na conservação de biodiversidade
no Quadrilátero Ferrífero; (d) gerar informações de base
sobre qualidade de água, biodiversidade de macroinvertebrados
bentônicos bioindicadores de qualidade de água no PARNA
Serra do Gandarela. Os principais resultados revelam que o
PARNA Serra do Gandarela é guardião de riachos de cabeceira
em condições de referência, com elevada diversidade de hábitats
aquáticos e ótima qualidade de água, onde vivem organismos
bentônicos sensíveis, tolerantes e resistentes à poluição. Sendo a
Serra do Gandarela responsável pela segurança hídrica de grande
parte dos municípios do Quadrilátero Ferrífero de Minas Gerais,
é extremamente importante que estes riachos em condições de
referência sejam conservados e utilizados em futuros estudos de
avaliação de impactos ambientais e programas de monitoramento
de condições ecológicas de longo prazo. As condições de
alta preservação devem servir como baliza de referência para
tomadores de decisão em processos de licenciamento ambiental de empreendimentos potencialmente causadores de impactos
ambientais e riscos à biodiversidade.
... Hill et al., 2017;Skultety & Matthews, 2018). By contrast, homogenisation of assemblages in streams draining modified landscapes was driven by (i) increasing similarity of abundance-based assemblage composition or (ii) increased occurrence of generalist species and/or the loss of species with narrow environmental niches (Hermoso, Clavero & Kennard, 2012;Mykrä & (Figure legend continued from previous page.) Fig. 4. Conceptual model 3 depicting how dispersal propensity and landscape connectivity drive directional change in beta diversity over time. ...
Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.
... Agricultural activity has strict negative impact on condition of surface water bodies, their ecosystems, the degradation of vegetation, and the quantitative and qualitative changes in fish populations in the Mediterranean basin [62]. The main factor affecting the Baltic Sea region environment is the increased amount of nutrients in rivers, mainly from diffuse agricultural sources [63]. ...
Twenty-four rivers in different parts of Lithuania were selected for the study. The aim of the research was to evaluate the impact of anthropogenic load on the ecological status of rivers. Anthropogenic loads were assessed according to the pollution sources in individual river catchment basins. The total nitrogen (TN) values did not correspond to the “good” and “very good” ecological status classes in 51% of the tested water bodies; 19% had a “bad” to “moderate” BOD7, 50% had “bad” to “moderate” NH4-N, 37% had “bad” to “moderate” NO3-N, and 4% had “bad” to “moderate” PO4-P. The total phosphorus (TP) values did not correspond to the “good” and “very good” ecological status classes in 4% of the tested water bodies. The largest amounts of pollution in river basins were generated from the following sources: transit pollution, with 87,599 t/year of total nitrogen and 5020 t/year of total phosphorus; agricultural pollution, with 56,031 t/year of total nitrogen and 2474 t/year of total phosphorus. The highest total nitrogen load in river basins per year, on average, was from transit pollution, accounting for 53.89%, and agricultural pollution, accounting for 34.47%. The highest total phosphorus load was also from transit pollution, totaling 58.78%, and agricultural pollution, totaling 28.97%. Multiple regression analysis showed the agricultural activity had the biggest negative influence on the ecological status of rivers according to all studied indicators.
... Although homogenization studies in freshwater fish assemblages are increasing, most part of them come from temperate latitudes of the Northern Hemisphere [e.g., [11][12][13][14][15][16][17][18][19][20], evidencing a remarkable geographical bias. Because the species diversity is differentially distributed between hemispheres, continents, and regions [2], it is desirable to know whether biotic homogenization occurs in areas beyond those most frequently reported [10,21]. ...
Aim:
Exotic species' introductions together with extinction of native species represent the main mechanisms driving biotic homogenization of freshwater fish assemblages around the world. While generally ichtyofaunistic realms transit towards biotic homogenization, for conservation purposes it is essential to understand what specific mechanisms are promoting it on particular areas or regions. Here, we report the occurrence of biotic homogenization in 29 Chilean watersheds, analyzing its β-diversity (including turnover and nestedness) and predicting future trends.
Location:
Continental Chile (18o-56o S).
Methods:
We determined fish composition per basin for historical and current assemblages; extant native, exotic, and extinct species were recorded as 1 (presence) or 0 (absence) in two matrices basins × species. For each matrix, we calculated the turnover (βsim), nestedness (βnes), and β-diversity (βsor); then, we obtained Δβsim, Δβnes, and Δβsor, as the arithmetical difference between basin pairs over time. In addition, we search for explanatory variables correlating Δβsim, Δβnes, and Δβsor with geographical and land use variables. Finally, simulating events of species introduction (i.e., invasion) and extinction, we generated 15 hypothetical assemblages, looking to establish future trends towards biotic change in Chilean basins.
Results:
Species turnover and β-diversity significantly decreased from historical to current assemblages (Δβsim = -0.084; Δβsor = -0.061, respectively), while the species nestedness did not show significant changes (Δβnes = 0.08). Biotic changes have been driven mainly by the introduction of 28 exotic species, with a minor role of extinctions (one species) and translocations (0 species) of native species. Changes in β-diversity were negatively correlated with area, elevation, and geographical distance between basins but not with land-use nor human population. Finally, the analysis of 15 future assemblages predicts a significant decrease of β-diversity and turnover, and an increase for species nestedness, this time promoted by an increase in the extinction of native species.
Main conclusion:
Chilean basins show a significant decrease of the distributional β-diversity and species turnover of the freshwater fish fauna, evidencing a trend towards biotic homogenization. This trend is shared with other Neotropical basins; however, specific mechanisms driving it show different magnitude. Changes in the β-diversity components do not show correlation with variables associated to land use, thus suggesting that casual introductions of freshwater fishes in Chile follow an opportunistic mode related to commercial use. According to future scenarios simulated, biotic homogenization should increase further, mainly as consequence of increased native extinctions.
... Biotic homogenization has become one of the most prominent and pressing topics in conservation biology (Rooney et al., 2007;Olden et al., 2010), yet only limited research has been conducted to elucidate the complex interactions of the multiple ecological and environmental determinants of this process (Rahel, 2000;Hermoso et al., 2012;Brice et al., 2017). A recent systematic review showed that several components of the biotic homogenization process remain unclear or unknown . ...
The conservation challenges facing freshwater ecosystems necessitate broadening our science from understanding individual species loss to anticipating multi-faceted changes to biodiversity. In recent decades, the process of biotic homogenization by which regional biotas become more similar through time has attracted considerable attention. Here, we (1) quantified spatial and temporal changes in taxonomic and functional similarity of fish assemblages among Neotropical reservoirs, (2) determined nonnative species contributions to changes in taxonomic and functional composition, and (3) evaluated relationships between the changes in taxonomic and functional similarity among reservoirs. We did so by considering different spatial scales: inter- and intra-ecoregions. At inter-ecoregion scale, reservoir fish assemblages have become taxonomically homogenized over time, whereas functional trait composition has tended to differentiate. At intra-ecoregion scale, we detected both taxonomic and functional differentiation over time. Despite these overall trends, different ecoregions exhibited considerable variation in patterns of fish faunal homogenization and differentiation. We found a moderate positive relationship between changes in mean taxonomic and functional similarity among reservoirs at inter-ecoregion scale, which was no longer evident within ecoregions. In conclusion, this study demonstrates the strong scale-dependence of perceived patterns in homogenization, and further highlights the magnitude of threats to freshwater biodiversity in the Neotropical ecosystems.
... For instance, fish beta diversity among streams subjected to agricultural land use and with a high concentration of phosphorus was reduced in relation to a group of reference streams (Johnson and Angeler 2014). Different mechanisms are involved in faunal homogenization (Rahel 2002), such as the invasion or introduction of non-native species, the local extinction of rare/specialist species and the concomitant spread of common/generalist species (Olden and Poff 2004;Hermoso et al. 2012). In riverine systems, the latter mechanism has been recorded in disturbed regions, where widespread fish species present in downstream sections colonize upstream streams (Walters et al. 2003). ...
Despite the importance of assessing beta diversity to understand the effects of human modifications on biological communities, there are almost no studies that properly addressed how beta diversity varies along anthropogenic gradients. We developed an algorithm to calculate beta diversity among a set of sites included in a moving window along any given environmental gradient. This allowed us to assess beta diversity among sites with similar conditions in terms of human modifications (e.g., land use or instream degradation). We investigated beta diversity using stream fish community data and indicators of human modification quantified at four spatial scales (whole catchment, riparian, local, and instream). Variation in beta diversity was dependent on the scale of human modifications (catchment, riparian, local, instream, and all four scales combined) and on the type of diversity considered (taxonomic or functional). We also found evidence for non-linear responses of both taxonomic and functional beta diversity to human-induced environmental alterations. Therefore, the response of beta diversity was more complex than expected, as it depended on the scale used to quantify human impact and exhibited opposite responses depending on the location along the environmental impact gradient and on whether the response was taxonomic or functional diversity. Anthropogenic modifications can introduce unexpected variability among stream communities, which means that low beta diversity may not necessarily indicate a degraded environmental condition and high beta diversity may not always indicate a reference environmental condition. This has implications for how we should consider beta diversity in environmental assessments.
... Due to the loss of native freshwater biodiversity worldwide (Strayer & Dudgeon, 2010), the need for the identification of priority areas for conservation (Hermoso, Clavero, & Kennard, 2012) and the limited conservation resources available; there are three main implications for future conservation strategies found in this paper: (a) not only headwaters require conservation measures but also large upland rivers are important in contributing to native fish diversity. These systems resulted in a low exotic species presence, promoting zones with high native diversity. ...
Aim
Exotic species are a major threat to biodiversity and have modified native communities worldwide. Invasion processes have been extensively studied, but studies on species richness and beta diversity patterns of exotic and native species are rare. We investigate such patterns among exotic and native fish communities in upland and lowland rivers to explore their relationship with environmental drivers.
Location
Northern Italy.
Methods
Exotic and native fish beta diversity patterns were investigated separately in lowland and upland sites using Local Contribution to Beta Diversity (LCBD) and Species Contribution to Beta Diversity (SCBD) analyses. To examine the main environmental variables affecting the LCBD, a Boosted Regression Trees (BRT) method was used. Community dispersion among and within stream orders was investigated with the PERMDISP test.
Results
In lowland sites, exotic species richness was higher than native species richness, especially in large rivers and drainage canals. An opposite trend was found in upland sites, where native species richness was higher than exotic species richness, especially in large rivers. No clear LCBD patterns were found along stream orders in the lowland, whereas higher stream orders in the upland showed the highest LCBD. Its patterns in upland and lowland sites were related to a number of factors, such as total suspended solids and total phosphorus. Community dispersion among stream orders did not show a relationship with environmental heterogeneity. SCBD values were positively correlated with species occupancy in the study area, and native species showed higher SCBD values than exotic species only in the uplands.
Main conclusions
Large rivers in the uplands are important in maintaining native fish diversity and should be protected against invasive fish. In contrast, most lowland rivers have suffered from biological homogenization. Some rare native species can show low contribution to beta diversity, but still need conservation actions due to their risk of local extinction.
... Agricultural land use has shown to have strong negative effects on water quality, stream habitat, and degradation of riparian vegetation, ultimately resulting in fish assemblages' impoverishment and clearly benefiting non-native species, which thrive under altered conditions [95]. The most negative effects were associated with intensive, heavily irrigated, fertilized, and pastured agricultural systems, mostly represented at the basin scale by olive groves, irrigated crops, and pastures. ...
Southern Europe has been shaped by human activity and maintained by traditional practices of land use for centuries. In the last decades a rather accelerated intensification of agricultural systems was observed, with consequent environmental effects. This study aimed to evaluate the effects of agricultural land use in two small-medium river basins in the South of Portugal, regarding: i) water quality and stream habitat; ii) fish fauna; iii) soil. Sampling took place in 2012 in nine stream sites located in the Azambuja and Alcáçovas river basins, where fish were captured, hydromorphological habitat features were assessed and water samples were collected. Additionally, soil samples were collected in nineteen dominant soil types from the slopes that drain into the stream section immediately upstream stream sites. Land use was quantified for each sampled site at the basin and local scales. Results showed negative effects on water quality and stream habitat, including increased sedimentation and nutrient loading, morphological and hydrological alterations, and degradation of riparian vegetation, ultimately resulting in fish assemblages’ impoverishment. The most negative effects were associated with intensive, heavily irrigated, fertilized and pastured local systems, mostly represented at the basin scale by olive groves, irrigated crops and pastures. Conversely, local agricultural intensity did not prove to be a threat to the integrity and quality of the soil, seeming to ensure the sustainability of the local uses and their systems. These are preliminary findings based on a case study, and more detailed research is further required to substantiate the results. Nevertheless, this study contributes to a comprehensive approach to the effects of agricultural land use, highlighting the need to integrate the results of different natural resources to efficiently support policy and decision-makers towards a sustainable agriculture, water management and land use planning.
Keywords: agricultural intensity, agricultural systems, water quality, stream habitat, fish assemblages, soil quality, sustainable agriculture, water management, land use planning.
... Humans rely on healthy freshwater ecosystems for the benefits and services they provide [30,32]. The fish faunas are homogenized by few non-native species, globally [33][34][35][36][37]. Illegal fishing using dynamite, pesticides, electrofishing are also major threats to fish biodiversity all over the world [38][39][40]. ...
The loss of biodiversity is one of the most reflective effects of humans on the global perspective and it is more
and more urgent to understand how this loss will affect and what will be the profound consequences to the ecosystem functioning. Non-native fishes can cause considerable adverse impacts on the function of aquatic ecosystems and loss of biodiversity. Ecology of ecosystem focuses on the fluctuation of energy and nutrients through ecological systems. It has been confirmed that the fishes are sensitive indicators of environmental degradation and alteration. Study was undertaken during the period of October 2015 to September 2016 from the Paisuni river, India. Fish faunas of the Paisuni river have harbors of 58 species belonging to 5 order, 18 family and 43 genera. Cypriniformes and Cyprinidae were the most rich fish species order and families, respectively from the river. The Cyprinidae family has highest harbors family with 25 fish species. The family Anabaniitidae has 5 fish species which is second dominant family from the Paisuni river. According to abundance, Cyprinus carpio and Oreochromis niloticus were powerfully invaded in the Paisuni river. The detonated frequency of O. niloticus and C. carpio was recorded from the Paisuni river. Exotic species is alarming for indigenous fish species biodiversity. C. carpio and O. niloticus are frequently recorded in the Ganga river. Very highly important and ecological indicator fish species, Tor mahseer, Tor tor is declining in the catch. Current ecosystem functioning is favour to non-native species from the Paisuni river.
... Humans rely on healthy freshwater ecosystems for the benefits and services they provide[30,32]. The fish faunas are homogenized by few non-native species, globally[33][34][35][36][37]. Illegal fishing using dynamite, pesticides, electrofishing are also major threats to fish biodiversity all over the world[38][39][40]. ...
The loss of biodiversity is one of the most reflective effects of humans on the global perspective and it is more
and more urgent to understand how this loss will affect and what will be the profound consequences to the ecosystem functioning. Non-native fishes can cause considerable adverse impacts on the function of aquatic ecosystems and loss of biodiversity. Ecology of ecosystem focuses on the fluctuation of energy and nutrients through ecological systems. It has been confirmed that the fishes are sensitive indicators of environmental degradation and alteration. Study was undertaken during the period of October 2015 to September 2016 from the Paisuni river, India. Fish faunas of the Paisuni river have harbors of 58 species belonging to 5 order, 18 family and 43 genera. Cypriniformes and Cyprinidae were the most rich fish species order and families, respectively from the river. The Cyprinidae family has highest harbors family with 25 fish species. The family Anabaniitidae has 5 fish species which is second dominant family from the Paisuni river. According to abundance, Cyprinus carpio and Oreochromis niloticus were powerfully invaded in the Paisuni river. The detonated frequency of O. niloticus and C. carpio was recorded from the Paisuni river. Exotic species is alarming for indigenous fish species biodiversity. C. carpio and O. niloticus are frequently recorded in the Ganga river. Very highly important and ecological indicator fish species, Tor mahseer, Tor tor is declining in the catch. Current ecosystem functioning is favour to non-native species from the Paisuni river.
... Moreover, the introduction of species is creating biotic homogenization, where species have gained locally in the short term, but there are losses of beta diversity and rare and unique species only in the long term (McKinney & Lockwood, 1999;Rahel, 2000;Olden et al., 2004Olden et al., , 2008Clavero & García-Berthou, 2006). Although this is usually understood to mean taxonomic homogenization (Rahel, 2000;Marchetti et al., 2001;Taylor, 2004;Clavero & García-Berthou, 2006;Clavero & Hermoso, 2011;Villéger et al., 2011;Hermoso et al., 2012;Petesse & Petrere, 2012;Pool & Olden, 2012;Magurran et al., 2015;Toussaint et al., 2016a), it is possible that fish communities can become more similar in terms of their functional properties (Buisson et al., 2013;Villéger et al., 2014). This fact is of growing concern, especially in regions such as the Neotropics that possess >75% of global fish functional diversity (Toussaint et al., 2016b). ...
The Reis et al. (2016) review, which addressed patterns of fish biodiversity and their conservation status in South America, failed to take into account several issues that are highlighted in this commentary. There is particular disagreement with their main conclusion: ‘ ...conservation status of South American freshwater fish faunas is better than in most other regions of the world’, given their arguments were based on questionable comparisons supported by a limited set of examples and with overconfidence in lists of threatened species that are clearly incomplete. The review is also incomplete because it ignores the introduction of non-native species, their sources and consequences of the biological invasion process, which are pivotal for many of the actual threats to fish and all aquatic biodiversity.
... Other studies investigating the homogenisation of fish communities include Taylor (2004), Hermoso et al. (2012), Glowacki and Penczak (2013), Li et al. (2013) and Vargas et al. (2015). ...
Biotic homogenisation is the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more locations over a specified time interval. Recent years have witnessed enhanced interest and research effort in the study of biotic homogenisation across taxonomic groups and geographic regions, with the first article published over 20 years ago. Despite sustained interest, past research efforts have been unevenly distributed with regard to taxonomic groups and ecosystems. Biotic homogenisation of vertebrate and plant communities have been studied the most, while invertebrates have received little attention. Concurrent with heightened quantification of biotic homogenisation, is continued clarification on the significant ecological, evolutionary and social consequences of this phenomenon. Biotic homogenisation is now considered one of the most prominent forms of biotic impoverishment worldwide, and it will likely continue to increase in response to anthropogenic forces associated with growing human populations.
Key Concepts
In the wake of continued human‐driven species invasions and extinctions, the process of biotic homogenisation has rapidly emerged as a topic of interest in conservation biology.
Biotic homogenisation is the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more locations over a specified time interval.
This is a unique research challenge, because it is a multifaceted process that subsumes many aspects of the modern biodiversity crisis, including species invasions, extirpations and environmental alteration.
Current knowledge of the patterns, mechanisms and implications of biotic homogenisation is highly variable across taxonomic groups, but in general is most complete for freshwater fishes, birds and plants.
Biotic homogenisation is an important dimension of the modern biodiversity crisis having significant ecological, evolutionary and social implications.
... Although a number of biotic homogenisation studies of freshwater fish assemblages have been completed, the majority have focused on taxonomic homogenisation in temperate latitudes of the Northern Hemisphere. In contrast, comparative studies between different regions or over multiple scales are lacking ), but see Villéger et al. (2011), Hermoso et al. (2012), and Vitule et al. (2012). A comparison of introductions across climatically similar regions promotes an understanding of invasion processes by isolating large-scale drivers other than regional climate ( Pauchard et al., 2004), and focuses on the role of human activities ( Jiménez et al., 2008) and the characteristics of the invading species (Moyle & Marchetti, 2006). ...
... This index ranges between 0 (no human influence) and 100 (very high human influence), and it is mapped at the global scale with a spatial resolution of 1 km (for details see Sanderson et al., 2002 and http://sedac.ciesin.columbia.edu/data/set/wildareas-v2human-footprint-geographic). Finally, given the important role of river regulation as a global threat to freshwater biodiversity (V€ or€ osmarty et al., 2010), particularly in the Iberian Peninsula (Hermoso et al., 2011a;Hermoso, Clavero & Kennard, 2012a;Clavero et al., 2013), we also checked the proportion of areas in Natura 2000 that contain at least one reservoir (sourced from the Global Reservoir and Dam database; Lehner et al., 2011; downloaded from http://atlas.gwsp.org/) and the proportion of Natura 2000 areas that have at least one reservoir downstream that constrains migration between the protected area and the ocean or river reaches downstream. ...
1. Although coverage by protected areas is increasing worldwide, their capacity to protect freshwater biodiversity is uncertain. This may be the case of the European Natura 2000, the world’s largest reserve network, given its primary focus on terrestrial biodiversity. We tested this hypothesis by assessing the effectiveness of Natura 2000 in protecting freshwater biodiversity and associated key ecological processes in the Iberian Peninsula, where more than 25% of land is under some kind of protection.
2. We compiled distributional data on 91 species of freshwater fish, amphibians and aquatic reptiles, at the subcatchment scale (≈20km2 9 resolution), for the whole Iberian Peninsula, and assessed the proportion of their ranges covered by Natura 2000. We also explored the coverage of the main environmental gradients, and the capacity of Natura 2000 to offer protection against human impacts. To do so, we evaluated land use intensity and the human footprint within and upstream of protected areas, both of which might compromise the protection of biodiversity. Finally, we also analysed the incidence of reservoirs within and downstream of protected areas.
3. Natura 2000 broadly covers the main environmental gradients in the Iberian Peninsula, but fails to provide sufficient coverage of freshwater biodiversity, with less than 20% of the range of species covered on average. This would be insufficient to achieve a modest conservation target of 25% of the range for more than 80% of species, including most of species specifically listed in the legislation. Moreover, although the network tends to comprise areas with the least human impact, it seems to be vulnerable to the propagation of upstream effects (intensive land use downstream) and the loss of downstream connectivity (reservoirs).
4. Large reserve networks, primarily designed to protect terrestrial biodiversity, 24 may not offer adequate protection for freshwater biodiversity. We recommend re-visiting the design of Natura 2000 to improve the representation of freshwater biodiversity and enhance its capacity to address threats and particular ecological needs, such as for migration. Given the high pressure on land and the poor condition of the remaining unprotected habitat, conservation efforts must minimise conflicts of interest and management costs.
... Global Ecology and Biogeography, © 2014 John Wiley & Sons Ltd intensity of change in taxonomic dissimilarity among pairs of fish assemblages was variable, but on average we found a weak trend towards taxonomic homogenization (Tables 1 & 2, Fig. 3), which is consistent with previous studies on freshwater fish faunas in Europe (Clavero & García-Berthou, 2006;Leprieur et al., 2008b;Villéger et al., 2011a;Hermoso et al., 2012). We also found that the contribution of turnover to dissimilarity tended to decrease, but this change was marked by a high variability among pairs of assemblages, a pattern also found at the global scale (Toussaint et al., 2014). ...
Aim
Human activities and the consequent extirpations of native species and introductions of non‐native species have been modifying the composition of species assemblages throughout the world. These anthropogenic impacts have modified the richness of assemblages as well as the biological dissimilarity among them. However, while changes in taxonomic dissimilarity (i.e. accounting for species composition) have been assessed intensively during the last decade there are still few assessments of changes in functional dissimilarity (i.e. accounting for the diversity of biological traits). Here, we assess the temporal changes in both taxonomic and functional dissimilarities for freshwater fish assemblages across E urope.
Location
Western P alaearctic, 137 river basins.
Methods
The J accard index was used to quantify the changes in both taxonomic and functional dissimilarity. We then partitioned dissimilarity to extract its turnover component and measured the changes in the contribution of turnover to dissimilarity.
Results
Functional homogenization exceeded taxonomic homogenization six‐fold. More importantly, we found only a moderate positive correlation between these changes. For instance, 40% of assemblages that experienced taxonomic differentiation were actually functionally homogenized. Taxonomic and functional homogenizations were stronger when the historical level of taxonomic dissimilarity among assemblages was high and when a high number of non‐native species were introduced in the assemblages. Moreover, translocated species (i.e. non‐native species originating from E urope) played a stronger role than exotic species (i.e. those coming from outside E urope) in this homogenization process, while extirpation did not play a significant role.
Main conclusions
Change in taxonomic diversity cannot be used to predict changes in functional diversity. In addition, as functional diversity has been proven to be a better indicator of ecosystem functioning and stability than taxonomic diversity, further studies are required to test the potential effects of functional homogenization at the local scale.
... Han et al., 2008). In the Iberian Peninsula, river stretches located near reservoirs have been shown to have high densities of introduced fish species, which again have a direct negative effect on the native fish fauna (Rinc on et al., 1990;Hermoso et al., 2011;Hermoso, Clavero & Kennard, 2012). Reservoirs also facilitate the spread of introduced species by acting as introduction centres and easing the establishment of new populations (e.g. ...
1. Introduced species often thrive in modified systems, although it is not clear whether they have
negative effects on native biota that might also be present or, alternatively, occupy niches that have
been left empty due to the original habitat modification.
2. We used 247 surveys of fish assemblages (48 species in all) in riverine reservoirs across the Iberian
Peninsula to analyse the relationships between the species richness of introduced and native fish.
Most of the samples (195) were from areas with a Mediterranean climate, while the reminder (52)
had a temperate climate.
3. Mediterranean reservoirs had more introduced than native species, with an opposite pattern in the
temperate areas. The richness of non-natives was positively related to the area of reservoir and
human pressures and negatively related to altitude. Native richness was higher in larger and deeper
reservoirs and lower in older and more impacted reservoirs, as well as in those with more introduced
piscivores.
4. There was a negative relationship between the richness of native fish and that of non-native piscivores
in Mediterranean reservoirs, confirmed through multiple regression and structural equation
modelling. Contrastingly, native fish richness was mainly controlled by variables related to water
quality in temperate areas, implying that the negative impacts of introduced fishes in reservoirs can
be context dependent.
5. The presence of introduced piscivores thus seems an important factor excluding many native fish
from reservoirs in Mediterranean environments in the Iberian Peninsula.
... Anthropogenic disturbance is one of the main drivers of biotic homogenization associated with changes in the natural colonization and extinction rates, in comparison with non-disturbed environments (Olden & Poff, 2003). Hence, there is evidence of increasing assemblage similarity under landscape transformation and urbanization in different groups of organisms, either vertebrates, for example birds and fishes (Blair, 2001;Hermoso et al., 2012), or invertebrates, for example beetles, spiders and butterflies (Dormann et al., 2007;Ekroos et al., 2010). ...
AimsHuman landscape disturbance can drive the degradation of natural environments, thereby contributing to indigenous (endemic and native non-endemic) species extinctions, facilitating the establishment of exotic species and ultimately resulting in more similar species compositions over time and space. We assessed whether similarities in epigean arthropod assemblages differ between indigenous and exotic species in an oceanic archipelago, and we also examined whether such assemblage similarities depend on the most dominant species, the island, the type of habitat, the degree of landscape disturbance or local environmental variables. LocationFour oceanic islands in the Azores archipelago, Portugal. Methods
We examined the degree of assemblage similarity and the effect of environmental variables and spatial disturbance to explain the epigean arthropod distributions for indigenous and exotic species. ResultsExotic species increased overall assemblage similarity. Distinct arthropod assemblages occurred on the different islands and in the different habitats. Assemblage differences between the habitats depended on the island. This pattern was largely explained by the abundance patterns of the most abundant indigenous and exotic species (ten indigenous and ten exotic species accounted for 75% of total individuals). In comparison with the high explanatory capacity of the habitats and islands per se, local environmental variables and disturbance hardly explained the assemblage composition in both groups of species. Main conclusionsWe demonstrate that exotic species promote assemblage homogenization on these oceanic islands, and that such process is contingent and independent between islands and habitats. General habitat characteristics seemed to be the main driver of assemblage structure, independently of the different climatic conditions or disturbance levels.
... New statistical approaches such as Quantile Regression (QR) and Structural Equation Modelling (SEM) allow better integration of sound ecological and statistical theory as well as the possibility of testing whether data are consistent with hypothesized causal pathways. Development of these approaches provides promising areas for future development (see Pittman et al. 2004;Vaz et al. 2008;Hermoso et al. 2011;Johnson et al. 2012). ...
Adoption of the ecosystem approach to fisheries management relies on recognition of the link between fish and other components of the ecosystem, namely their physical and biological habitat. However, identifying the habitat requirements of marine fishes and hence determining their distribution in space and time is scientifically complex. We analysed the methodologies and findings of research on temperate, demersal fish habitat requirements to highlight the main developments in this field and to identify potential shortfalls. Many studies were undertaken over large spatial scales (≥100s km2) and these generally correlated abundances of fish to abiotic variables. Biological variables were accounted for less often. Small spatial scale (≤m2), experimental studies were comparatively sparse and commonly focused on biotic variables. Whilst the number of studies focusing on abiotic variables increased with increasing spatial scale, the proportion of studies finding significant relationships between habitat and fish distribution remained constant. This mismatch indicates there is no justification for the tendency to analyse abiotic habitat variables at large spatial scales. Innovative modelling techniques and habitat mapping technologies are developing rapidly, providing new insights at the larger spatial scales. However, there is a clear need for a reduction in study scale, or increase in resolution additional to the integration of biotic variables. We argue that development of sound predictive science in the field of demersal fish habitat determination is reliant on a change in focus along these lines. This is especially important if spatial management strategies, such as Marine Protected Areas (MPA) or No Take Zones (NTZ), are to be used in future ecosystem-based approaches to fisheries management.
... Although a number of biotic homogenisation studies of freshwater fish assemblages have been completed, the majority have focused on taxonomic homogenisation in temperate latitudes of the Northern Hemisphere. In contrast, comparative studies between different regions or over multiple scales are lacking (Olden et al., 2010, 2011), but see Villéger et al. (2011), Hermoso et al. (2012), and Vitule et al. (2012). A comparison of introductions across climatically similar regions promotes an understanding of invasion processes by isolating large-scale drivers other than regional climate (Pauchard et al., 2004), and focuses on the role of human activities (Jiménez et al., 2008) and the characteristics of the invading species (Moyle & Marchetti, 2006). ...
Mediterranean-climate regions (med-regions) are global hotspots of endemism facing mounting environmental threats associated with human-related activities, including the ecological impacts associated with non-native species introduc-tions. We review freshwater fish introductions across med-regions to evaluate the influences of non-native fishes on the biogeography of taxonomic and func-tional diversity. Our synthesis revealed that 136 freshwater fish species (26 families, 13 orders) have been introduced into med-regions globally. These introductions, and local extirpations, have increased taxonomic and functional faunal similarity among regions by an average of 7.5% (4.6–11.4%; Jaccard) and 7.2% (1.4–14.0%; Bray–Curtis), respectively. Faunal homogenisation was highest in Chile and the western Med Basin, whereas sw Cape and the Aegean Sea drainages showed slight differentiation (decrease in faunal similarity) over time. At present, fish faunas of different med-regions have widespread species in common (e.g. Gambusia holbrooki, Cyprinus carpio, Oncorhynchus mykiss, Carassius auratus, and Micr-opterus salmoides) which are typically large-bodied, non-migratory, have higher physiological tolerance, and display fast population growth rates. Our findings suggest that intentional and accidental introductions of Electronic supplementary material The online version of this article (doi:10.1007/s10750-013-1486-9) contains supplementary material, which is available to authorized users.
Anthropogenic introduction of non-native species has occurred since the first European colonization of South America in the 1500s, with the Atlantic Forest being the most heavily affected biome in the continent. Biological invasions, together with other anthropogenic pressures occurring over the subsequent 500 years, led to many biological changes such as biotic homogenization. In this chapter, we discuss patterns of non-native species introductions, highlight invasions or population explosions of problematic native species, and explore the phenomenon of biotic homogenization in the Atlantic Forest, Brazil. We explore examples related to the effect of recent introductions of non-native species, highlighting the loss of native biodiversity (e.g., rare, specialist, and endemic) and the proliferation of human-mediated non-native species of economic importance (e.g., genrealist, common and widely distributed). We also discuss the role of society and policymakers in developing policies of public interest. Finally, we discuss how raising awareness of the negative effects of invasive non-native species will contribute to inform management policies and provoke more in-depth research, resulting in greater protection and sound management strategy for the Atlantic Forest.
Australoheros facetus is a neotropical cichlid and an exotic species in the Guadiana and Odelouca basins (Southern Portugal). In this research, we aimed to characterize the main behavioural patterns and circulating hormones, 17β-estradiol (E2) for females, and testosterone, 11-ketotestosterone (11KT) and cortisol for both sexes during the formation of social groups, a crucial step in the life-history of A. facetus. A pair-breeding strategy with territorial behaviour and aggressive interactions was found, with a positive correlation between dominance and size for both sexes. There were no significant differences between non-territorial and territorial individuals in the baseline levels of hormones, but 11KT was higher in males when they became territorial, as E2 for territorial females, while there was no clear pattern for testosterone. In contrast, cortisol was higher in non-territorial males and correlated negatively with social dominance. These results suggest that size is the main driver for social dominance and that formation of stable hierarchies result in higher circulating 11KT and lowers stress in territorial males. Related to A. facetus' behaviour, aggressiveness and biparental care may be an advantage during the invasion process of A. facetus, facilitating colonization of new habitats.
Non-native species introduced into reservoirs cause major changes in biodiversity, resulting in spatial and temporal biotic homogenization and/or differentiation. We used a sampling standardized temporally and spatially in reservoirs of basins located in the Neotropics, the Coastal, Iguaçu, and Upper Paraná basins. Our analyses were conducted at the interbasin and intrabasin scales, aimed at: (i) identifying the non-native species and their major vectors of introductions, (ii) assessing temporal and spatial changes in the fish assemblages, and (iii) evaluating temporal changes in the beta diversity of the basins/reservoirs. The spatial occupation of non-native species was variable, with Tilapia
rendalli, Cyprinus carpio and Oreochromis niloticus the most frequently introduced species. This highlights aquaculture as the main vector of invasives on a large spatial scale. The percentage of non-native species at the interbasin and intrabasin scales increased over time. Temporal comparisons of the fishes support the hypothesis that biotic homogenization occurred at the interbasin scale, whereas the biotic differentiation was observed at the intrabasin scale. Beta diversity decreased over time at the interbasin and intrabasin scales, with decrease in species richness serving as the variable that best explained changes in biological diversity. There was no relation between beta diversity and time for the Iguaçu.
The decline of native fish populations and the invasion of non-native fishes are the most noticeable trends in California's freshwater fish assemblages over the last century (Moyle and Williams 1990, Moyle 2000). Moyle (2000) and Dill and Cordone (1997) date the first introduction of non-native fish into California back to the latter half of the 19th Century. Yoshiyama et al. (1998) place the beginning of the decline of the state's chinook salmon populations also near the turn of the century. The mid-1800's also marks the beginning of a population explosion in California, driven by the discovery of gold in the Sierra Nevada in 1848.
Assemblages of native stream fishes in California show a remarkable ability to resist invasion by introduced fishes as long as the streams are relatively undisturbed by human activity. Previous studies had indicated a high degree of spatial (microhabitat) segregation among the native fishes, which was confirmed by a principal components analysis of microhabitat use data from Deer Creek, a tributary of the Sacramento River. A null modelling study using the same data set was performed to see if competition was a major force structuring the assemblage, because theoretical studies had indicated that a competitively structured assemblage should be most able to resist invasions. The null models indicated that competition was not the major structuring force, so it is likely the assemblages are structured through a combination of morphological specialization (reflecting evolutionary history), predation, and some competition. The assemblages resist invasion through both environmental and biotic factors. Predation seems to be an especially important biotic factor.
We tested the hypothesis that urbanization alters stream sediment regimes and homogenizes fish assemblages in 30 sub-basins of the Etowah River. Sediment variables included average particle size (mean phi) of the stream bed, percent fines (<2 mm) in riffles, and baseflow turbidity (NTU). Homogenization was quantified as ratios of endemic to cosmopolitan species richness (Er:Cr) and abundance (Ea:Ca). High NTU and fine stream beds were associated with homogenized assemblages (i.e., lower E:C ratios). Mean phi and NTU were significantly correlated with E:C ratios (r = −0.74 to −0.76) and, when combined using multiple regression, accounted for 73% of the variance in ratios. Stream slope strongly covaried with mean phi (r = −0.92) and percent fines in riffles (r = −0.79), but multiple regression models showed that urbanized sites had finer beds and riffles than predicted by slope alone. Urban land cover was the primary predictor of NTU (r
2
= 0.42) and, combined with slope in multiple regression, explained 51% of the variance in NTU. Our results indicate that stream slope is a background variable predicting particle size and E:C ratios in these streams. Urbanization disrupts these relationships by transforming clear streams with coarse beds into turbid streams with finer beds. These conditions favor cosmopolitan species, ultimately homogenizing fish assemblages. Bed texture was linked to urbanization; however, NTU was the best indicator of urban impacts because it was statistically independent from slope.
Faunal homogenization and differentiation occur when geographic regions show increased or decreased, re- spectively, similarity to each other in species composition owing to introductions and extinctions or extirpations. I used species presence-absence data for "native" (i.e., estimated species compositions before European settlement) and "total" (i.e., including nonnative fishes and extinctions) faunas to examine faunal similarity of freshwater fishes among aquatic ecoregions of British Columbia and among Canadian provinces and territories. British Columbia ecoregions showed faunal differentiation as the mean Jaccard's faunal similarity coefficient for total faunas was significantly less than that for native faunas (31.4% versus 34.9%), but some ecoregions showed homogenization (e.g., Vancouver Island and Columbia River ecoregions). Comparisons across Canada showed low but significant homogenization; average pairwise Jaccard's coefficient was higher in total versus native faunas (29.1% similarity versus 27.8%, respectively). British Columbia's fish fauna increased the most in similarity to other areas (except the three territories), with an average increase of 4.9%. Native faunal similarity patterns are part of Canada's natural heritage but are threatened by human- mediated increases in nonnative species and extinctions. This analysis provides a baseline to track changes in inter- regional faunal relationships at different geographic scales. Résumé : L'homogénéisation et la différentiation de la faune se produisent lorsque des régions géographiques présen- tent des compositions spécifiques respectivement plus semblables ou moins similaires à cause d'introductions ou
Freshwater ecosystems are at the forefront of the global biodiversity crisis, with more declining and extinct species than in terrestrial or marine environments. Hydrologic alterations and biological invasions represent two of the greatest threats to freshwater biota, yet the importance of linkages between these drivers of environmental change remains uncertain. Here, we quantitatively test the hypothesis that impoundments facilitate the introduction and establishment of aquatic invasive species in lake ecosystems. By combining data on boating activity water body physicochemistry, and geographical distribution of five nuisance invaders in the Laurentian Great Lakes region, we show that non-indigenous species are 2.4 to 300 times more likely to occur in impoundments than in natural lakes, and that impoundments frequently support multiple invaders. Furthermore, comparisons of the contemporary and historical landscapes revealed that impoundments enhance the invasion risk of natural lakes by increasing their proximity to invaded water bodies, highlighting the role of human-altered ecosystems as "stepping-stone" habitats for the continued spread of freshwater invaders.
Freshwater habitats occupy ,1% of the Earth's surface, yet are hotspots that support ,10% of all known species, and ,M of vertebrate species. Fresh waters also are hotspots for human activities that have led to widespread habitat degradation, pollution, flow regulation and water extraction, fisheries overexploitation, and alien species introductions. These impacts have caused severe declines in the range and abundance of many freshwater species, so that they are now far more imperiled than their marine or terrestrial counterparts. Here, we review progress in conservation of freshwater biodiversity, with a focus on the period since 1986, and outline key challenges for the future. Driven by rising conservation concerns, freshwater ecologists have conducted a great deal of research over the past 25 y on the status, trends, autecology, and propagation of imperiled species, threats to these species, the consequences of biodiversity loss for ecosystem functioning, metapopulation dynamics, biodiversity hotspots, reserve design, habitat restoration, communication with stakeholders, and weaknesses of protective legislation. Nevertheless, existing efforts might be insufficient to stem the ongoing and coming multitude of freshwater extinctions. We briefly discuss 4 important challenges for freshwater conservation. First, climate change will imperil both freshwater species and human uses of fresh water, driving engineering responses that will further threaten the freshwater biota. We need to anticipate both ecological and human responses to climate change, and to encourage rational and deliberate planning of engineering responses to climate change before disasters strike. Second, because freshwater extinctions are already well underway, freshwater conservationists must be prepared to act now to prevent further losses, even if our knowledge is incomplete, and engage more effectively with other stakeholders. Third, we need to bridge the gap between freshwater ecology and conservation biology. Fourth, we suggest that scientific societies and scholarly journals concerned with limnology or freshwater sciences need to improve their historically poor record in publishing important papers and influencing practice in conservation ecology. Failure to meet these challenges will lead to the extinction or impoverishment of the very subjects of our research.
Determining the strengths of interactions among species in natural communities presents a major challenge to ecology. Using an approach combining experimental perturbations and path analysis, I examined the mechanisms by which birds directly and indirectly affected other members of an intertidal community, evaluated alternative causal hypotheses, and predicted whether interactions among other unmanipulated species would be strong or weak. Comparing treatments with t tests indicated that excluding bird predators with cages caused increases in Pollicipes polymerus, and declines in Nucella spp., Mytilus californianus, and Semibalanus cariosus. However, these conclusions provided no insight into the underlying mechanisms causing the differences. Path analysis permitted insight into the causal mechanisms by making a variety of predictions about the strength of direct interactions: (a) Bird predation negatively affects Pollicipes, but not Nucella, Leptasterias, or Mytilus; (b) Pollicipes reduces Semibalanus and Mytilus abundance because of space competition; (c) Mytilus reduces Semibalanus cover through competition for space; and (d) as prey species, Semibalanus and Pollicipes enhance Nucella density, but Nucella predation does not have important effects on Semibalanus or Pollicipes. Based on the estimated strength of direct interactions, the importance of indirect effects among species could also be predicted. In experiments manipulating Nucella, Pollicipes, Semibalanus, and birds independently of one another, I tested 11 of the interactions predicted by the path analysis; all were supported. Path analysis in conjunction with limited experiments may provide an efficient means to predict important direct and indirect interactions among unmanipulated species within ecological communities.
The extensive construction of reservoirs over the past century has radically altered the environmental landscape on a global scale. Construction of dams on most large rivers has interrupted the connectivity of water flow and greatly increased the abundance of standing freshwater habitats. Reservoirs act as stepping-stones for the dispersal of exotic species across landscapes. A variety of passively dispersing species have invaded reservoirs, spread through interconnected waterways, and been transported to nearby disconnected habitats. We hypothesize that reservoirs are more readily invaded than natural lakes, because of their physiochemical properties, greater connectivity, and higher levels of disturbance. Here we summarize properties of reservoirs that would make them prone to invasions and discuss cases in which reservoirs have facilitated rapid range expansion. Our overview illustrates linkages between two important forms of global environmental change: the widespread manipulation of river flows and the accelerating spread of exotic species.
Aim Biotic homogenization describes the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more biotas over a specified time interval. The study of biotic homogenization is a young and rapidly emerging research area in the budding field of conservation biogeography, and this paper aims to synthesize our current knowledge of this process and advocate a more systematic approach to its investigation.
Methods Based on a comprehensive examination of the primary literature this paper reviews the process of biotic homogenization, including its definition, quantification, underlying ecological mechanisms, environmental drivers, the empirical evidence for different taxonomic groups, and the potential ecological and evolutionary implications. Important gaps in our knowledge are then identified, and areas of new research that show the greatest promise for advancing our current thinking on biotic homogenization are highlighted.
Results Current knowledge of the patterns, mechanisms and implications of biotic homogenization is highly variable across taxonomic groups, but in general is incomplete. Quantitative estimates are almost exclusively limited to freshwater fishes and plants in the United States, and the principal mechanisms and drivers of homogenization remain elusive. To date research has focused on taxonomic homogenization, and genetic and functional homogenization has received inadequate attention. Trends over the past decade, however, suggest that biotic homogenization is emerging as a topic of greater research interest.
Main conclusions My investigation revealed a number of important knowledge gaps and priority research needs in the science of biotic homogenization. Future studies should examine the homogenization process for different community properties (species occurrence and abundance) at multiple spatial and temporal scales, with careful attention paid to the various biological mechanisms (invasions vs. extinctions) and environmental drivers (environmental alteration vs. biotic interactions) involved. Perhaps most importantly, this research should recognize that there are multiple possible outcomes resulting from the accumulation of species invasions and extinctions, including biotic differentiation whereby genetic, taxonomic or functional similarity of biotas decreases over time.
Ongoing species invasions and extinctions are changing biological diversity in different ways at different spatial scales. Biotic homogenization (or BH) refers to the process by which the genetic, taxonomic or functional similarities of regional biotas increase over time. It is a multifaceted process that encompasses species invasions, extinctions and environmental alterations, focusing on how the identities of species (or their genetic or functional attributes) change over space and time. Despite the increasing use of the term BH in conservation biology, it is often used erroneously as a synonym for patterns of species invasions, loss of native species or changes in species richness through time. This reflects the absence of an agreed-upon, cogent definition of BH. Here, we offer an operational definition for BH and review the various methodologies used to study this process. We identify the strengths and weaknesses of these approaches, and make explicit recommendations for future studies. We conclude by citing the need for researchers to: (1) consider carefully the definition of BH by recognizing the genetic, taxonomic and functional realms of this process; (2) recognize that documenting taxonomic homogenization requires tracking the identity of species (not species richness) comprising biotas through space and time; and (3) employ more rigorous methods for quantifying BH.
The Guadiana River basin’s freshwater fish species richness, endemicity and threatened status (92% of native species are threatened)
highlight the need for a large-scale study to identify priority areas for their conservation. One of the most common problems
in conservation planning is the assessment of a site’s relative value for the conservation of regional biodiversity. Here
we used a two-tiered approach, which integrates an assessment of biodiversity loss and the evaluation of conservation value
through site-specific measures. These measures based on the reference condition approach introduce the ability to make objective
comparisons throughout the Guadiana River basin, thus avoiding a priori target areas. We identified a set of biodiversity
priority areas of special conservation significance—which contain rare taxa as well as intact fish communities—because of
their outstanding contribution to the basin’s biodiversity. The inclusion of complete sub-basins in these priority areas might
guarantee an optimal solution in terms of spatial aggregation and connectivity. However, the high spatial fragmentation to
which the Guadiana River basin is submitted due to river regulation highlights the necessity of a systematic approach to evaluate
the capability of the identified priority areas to maintain the Guadiana’s freshwater fish biodiversity.
Protocols for bioassessment often relate changes in summary metrics that describe aspects of biotic assemblage structure and
function to environmental stress. Biotic assessment using multimetric indices now forms the basis for setting regulatory standards
for stream quality and a range of other goals related to water resource management in the USA and elsewhere. Biotic metrics
are typically interpreted with reference to the expected natural state to evaluate whether a site is degraded. It is critical
that natural variation in biotic metrics along environmental gradients is adequately accounted for, in order to quantify human
disturbance-induced change. A common approach used in the IBI is to examine scatter plots of variation in a given metric along
a single stream size surrogate and a fit a line (drawn by eye) to form the upper bound, and hence define the maximum likely
value of a given metric in a site of a given environmental characteristic (termed the ‘maximum species richness line’ – MSRL).
In this paper we examine whether the use of a single environmental descriptor and the MSRL is appropriate for defining the
reference condition for a biotic metric (fish species richness) and for detecting human disturbance gradients in rivers of
south-eastern Queensland, Australia. We compare the accuracy and precision of the MSRL approach based on single environmental
predictors, with three regression-based prediction methods (Simple Linear Regression, Generalised Linear Modelling and Regression
Tree modelling) that use (either singly or in combination) a set of landscape and local scale environmental variables as predictors
of species richness. We compared the frequency of classification errors from each method against set biocriteria and contrast
the ability of each method to accurately reflect human disturbance gradients at a large set of test sites. The results of
this study suggest that the MSRL based upon variation in a single environmental descriptor could not accurately predict species
richness at minimally disturbed sites when compared with SLR’s based on equivalent environmental variables. Regression-based
modelling incorporating multiple environmental variables as predictors more accurately explained natural variation in species
richness than did simple models using single environmental predictors. Prediction error arising from the MSRL was substantially
higher than for the regression methods and led to an increased frequency of Type I errors (incorrectly classing a site as
disturbed). We suggest that problems with the MSRL arise from the inherent scoring procedure used and that it is limited to
predicting variation in the dependent variable along a single environmental gradient.
During the past decade there has been an explosion in computation and information technology. With it have come vast amounts of data in a variety of fields such as medicine, biology, finance, and marketing. The challenge of understanding these data has led to the development of new tools in the field of statistics, and spawned new areas such as data mining, machine learning, and bioinformatics. Many of these tools have common underpinnings but are often expressed with different terminology. This book describes the important ideas in these areas in a common conceptual framework. While the approach is statistical, the emphasis is on concepts rather than mathematics. Many examples are given, with a liberal use of color graphics. It should be a valuable resource for statisticians and anyone interested in data mining in science or industry. The book's coverage is broad, from supervised learning (prediction) to unsupervised learning. The many topics include neural networks, support vector machines, classification trees and boosting---the first comprehensive treatment of this topic in any book. This major new edition features many topics not covered in the original, including graphical models, random forests, ensemble methods, least angle regression & path algorithms for the lasso, non-negative matrix factorization, and spectral clustering. There is also a chapter on methods for "wide" data (p bigger than n), including multiple testing and false discovery rates. Trevor Hastie, Robert Tibshirani, and Jerome Friedman are professors of statistics at Stanford University. They are prominent researchers in this area: Hastie and Tibshirani developed generalized additive models and wrote a popular book of that title. Hastie co-developed much of the statistical modeling software and environment in R/S-PLUS and invented principal curves and surfaces. Tibshirani proposed the lasso and is co-author of the very successful An Introduction to the Bootstrap. Friedman is the co-inventor of many data-mining tools including CART, MARS, projection pursuit and gradient boosting.
Traditional methods of establishing control sites in field-oriented biomonitoring studies of water quality are limited. The reference-condition approach offers a powerful alternative because sites serve as replicates rather than the multiple collections within sites that are the replicates in traditional designs using inferential statistics. With the reference-condition approach, an array of reference sites characterises the biological condition of a region; a test site is then compared to an appropriate subset of the reference sites, or to all the reference sites with probability weightings. This paper compares the procedures for establishing reference conditions, and assesses the strengths and deficiencies of multimetric (as used in the USA) and multivariate methods (as used in the UK, Canada, and Australia) for establishing water-quality status. A data set of environmental measurements and macroinvertebrate collections from the Fraser River, British Columbia, was used in the comparison. Precision and accuracy of the 2 multivariate methods tested (AUStralian RIVer Assessment Scheme: AusRivAS, Benthic Assessment of SedimenT: BEAST) were consistently higher than for the multimetric assessment. Classification by ecoregion, stream order, and biotic group yielded precisions of 100% for the AusRivAS, 80-100% for the BEAST, and 40-80% for multimetrics; and accuracies of 100%, 100%, and 38-88%, respectively. Multimetrics are attractive because they produce a single score that is comparable to a target value and they include ecological information. However, not all information collected is used, metrics are often redundant in a combination index, errors can be compounded, and it is difficult to acquire current procedures. Multivariate methods are attractive because they require no prior assumptions either in creating groups out of reference sites or in comparing test sites with reference groups. However, potential users may be discouraged by the complexity of initial model construction. The complementary emphases in the multivariate methods examined (presence/absence in AusRivAS cf. abundance in BEAST) lead us to recommend that they be used together, and in conjunction with, multimetric studies.
The relative efficiency of single-pass electrofishing of longer stream sections vs. double-pass electrofishing of shorter reaches was evaluated in small (<5 m wide) wadable lowland streams in the Lake Balaton basin, Hungary. Two hundred meters long stream sections at 8 sites were divided into ten 20 m long sampling units each. These units were used to estimate the representativeness of species richness, species composition and relative abundance data at each level of sampling effort (single vs. double-pass, and number of sampling units pooled) using rarefaction and similarity-based approaches. Assemblage variables showed strong response to the length of the stream sampled (number of sampling units pooled). However, no differences were found between the single- and double-pass methods at any level of sample size for any assemblage variable. Estimates of species richness and species occurrence distributions required more sampling effort than estimates of species relative abundances, using any evaluation method. If a proxy estimate of sample representativeness cannot be obtained in the field, a minimum sampling of single-pass electrofishing of 100 m long sections may be necessary even in small wadable streams with low level of habitat and assemblage diversity to get a relatively unbiased picture on assemblage characteristics.
The realization of conservation goals requires strategies for managing
whole landscapes including areas allocated to both production and protection.
Reserves alone are not adequate for nature conservation but they are the cornerstone
on which regional strategies are built. Reserves have two main roles. They
should sample or represent the biodiversity of each region and they should
separate this biodiversity from processes that threaten its persistence. Existing
reserve systems throughout the world contain a biased sample of biodiversity,
usually that of remote places and other areas that are unsuitable for commercial
activities. A more systematic approach to locating and designing reserves
has been evolving and this approach will need to be implemented if a large
proportion of today's biodiversity is to exist in a future of increasing numbers
of people and their demands on natural resources.
Biotic homogenization is the increased similarity of biotas over time caused by the replacement of native species with nonindigenous species, usually as a result of introductions by humans. Homogenization is the outcome of three interacting processes: introductions of normative species, extirpation of native species, and habitat alterations that facilitate these two processes. A central aspect of the homogenization process is the ability of species to overcome natural biogeographic barriers either through intentional transport by humans or through colonization routes created by human activities. Habitat homogenization through reservoir construction contributes to biotic homogenization as local riverine faunas are replaced with cosmopolitan lentic species. The homogenization process has generally increased biodiversity in most freshwater faunas, as the establishment of new species has outpaced the extinction of native species. There are important exceptions, however, where the establishment of nonindigenous species has had devastating impacts on endemic species. The homogenization process appears Rely to continue, although it could be slowed through reductions in the rate of invasions and extirpations and by rehabilitating aquatic habitats so as to favor native species.
It is commonly held that species loss is linked to human population size
but there are surprisingly few quantitative studies that measure the
strength and nature of this linkage. In a study of about 150 nations,
a highly significant positive relationship (P << 0.01) was found between
population size and threat levels of birds and mammals. For continental
nations, log population explains 16-33% of the variation in threat level
among nations. The pattern of the continental population-threat correlation
indicates that per
capita human impacts are initially very high and
asymptotically diminish with increasing population size. No
population-threat correlation was found for island nations, since
human impacts are apparently so catastrophic that human population
size is largely irrelevant. Surprisingly, for both islands and continents,
area does not affect the level of threat after human population size is
accounted for. Thus, even on continents the harmful impacts of humans,
for a given population size, are evidently so profound that no amount of
added area provides compensatory refugia for native species. Major regional
differences in levels of threat are shown, with nations in Asia and the
Middle East having generally higher proportions of threatened species
than nations in Africa. The causes of these differences are only partly
related to population size. Other factors not related to population size
are that Asian nations tend to have much higher rates of mammal
over-harvesting and Middle Eastern nations tend to have statistically
lower percentages of area set aside as preserves. Threat proportions are
correlated between birds and mammals among nations implying that one group
may be a proxy indicator of impacts on the other. The slope of this
relationship indicates that mammals suffer more losses during initial
human impacts but proportions of threatened birds increase more rapidly
than mammals as human impacts become more widespread.
Information theory and log-likelihood models - a basis for model selection and inference practical use of the information theoretic approach model selection uncertainty with examples Monte Carlo insights and extended examples statistical theory.
Biotic homogenization is the increased similarity of biotas over time caused by the replacement of native species with nonindigenous species, usually as a result of introductions by humans. Homogenization is the outcome of three interacting processes: introductions of nonnative species, extirpation of native species, and habitat alterations that facilitate these two processes. A central aspect of the homogeniza-tion process is the ability of species to overcome natural biogeographic barriers either through intentional transport by humans or through colonization routes created by hu-man activities. Habitat homogenization through reservoir construction contributes to biotic homogenization as local riverine faunas are replaced with cosmopolitan lentic species. The homogenization process has generally increased biodiversity in most freshwater faunas, as the establishment of new species has outpaced the extinction of native species. There are important exceptions, however, where the establishment of nonindigenous species has had devastating impacts on endemic species. The ho-mogenization process appears likely to continue, although it could be slowed through reductions in the rate of invasions and extirpations and by rehabilitating aquatic habitats so as to favor native species.
Key Words flooding, drying, human impact s Abstract Streams in mediterranean-climate regions (areas surrounding the Mediterranean Sea, parts of western North America, parts of west and south Australia, southwestern South Africa and parts of central Chile) are physically, chemically, and biologically shaped by sequential, predictable, seasonal events of flooding and drying over an annual cycle. Correspondingly, aquatic communities undergo a yearly cycle whereby abiotic (environmental) controls that dominate during floods are reduced when the discharge declines, which is also a time when biotic controls (e.g. predation, compe-tition) can become important. As the dry season progresses, habitat conditions become harsher; environmental pressures may again become the more important regulators of stream populations and community structure. In contrast to the synchronous input of autumn litterfall in forested temperate streams, riparian input to mediterranean-type streams is more protracted, with fall and possibly spring peaks occurring in streams in the Northern Hemisphere and a summer peak existing in their Southern Hemisphere counterparts. We present 25 testable hypotheses that relate to the influence of the stream hydrograph on faunal richness, abundance, and diversity; species coexistence; seasonal changes in the relative importance of abiotic and biotic controls on the bi-otic structure; riparian inputs and the relative importance of heterotrophy compared to autotrophy; and the impact of human activities on these seasonally water-stressed streams. Population increases in mediterranean-climate regions (particularly in fer-tile regions) result in an intensification of the competition for water among different users; consequently, water abstraction, flow regulation, increased salinity, and pollu-tion severely limit the ability of the streams to survive as sustainable, self-regulated systems.
Widespread introduction of common species coupled with extirpa-tion of endemic species can cause fish assemblages to lose much of their regional uniqueness. This process of biotic homogenization contrasts with biotic differenti-ation, whereby initially similar fish faunas diverge due to introductions of different species. The relative importance of homogenization and differentiation in altering fish faunas has been examined across the world. Synthesis of these studies indi-cates that homogenization of fish faunas has been widespread and that introduc-tions, especially of sport fishes, have played a bigger role in altering fish faunas than extirpations. In the United States, pairs of states now average 15.4 more species in common than before European settlement. Additionally, the 89 pairs of states that formerly had no fish species in common now share an average of 25.2 spe-cies. While homogenization is prevalent at large spatial scales, differentiation of fish faunas is evident at intermediate spatial scales such as among watersheds within an ecoregion. This differentiation is largely the result of the idiosyncratic nature of fish introductions among individual lakes and streams. In general, translocated species (i.e., species that are native somewhere in the region but that have been moved to new locations) cause homogenization, whereas exotic species (species not native to the region) cause differentiation. Habitat and flow homogenization are major driv-ers of biotic homogenization because altered habitats create conditions that favor a few generalist species at the expense of more-specialized endemic species.
Backpack electrofishing is a common method used to compare total species richness and relative abundance of stream fishes across space and time. However, as with any sampling method, it is important to evaluate the sampling effort necessary to capture patterns of variation in fish assemblage structure across samples. Thus, we evaluated the efficacy of single-pass versus multiple-pass backpack electrofishing for minnows and darters in intermittent prairie streams. We found that in 14 of 19 three-pass electrofishing samples, we detected all species during the first pass. The samples where we missed species on the first pass were in pools with six to nine species, suggesting a single-pass sample worked best for pools with lower species richness. We also found that both the raw abundance (i.e., catch rates) and rank abundance of four common species based on the first pass is highly concordant with the second and third passes. Nevertheless, differences in capture efficiency varied by species and density. In particular, our ability to deplete a species from a stream pool was highly variable when fish densities were low, and for Phoxinus erythrogaster, it was variable across all densities. Overall, our data suggest single-pass electrofishing can be used to detect spatial and temporal trends in abundance and species richness given standardized effort, but may not be representative of absolute population densities.
Current circumstances — that the majority of species distribution records exist as presence-only data (e.g. from museums and herbaria), and that there is an established need for predictions of species distributions — mean that scientists and conservation managers seek to develop robust methods for using these data. Such methods must, in particular, accommodate the difficulties caused by lack of reliable information about sites where species are absent. Here we test two approaches for overcoming these difficulties, analysing a range of data sets using the technique of multivariate adaptive regression splines (MARS). MARS is closely related to regression techniques such as generalized additive models (GAMs) that are commonly and successfully used in modelling species distributions, but has particular advantages in its analytical speed and the ease of transfer of analysis results to other computational environments such as a Geographic Information System. MARS also has the advantage that it can model multiple responses, meaning that it can combine information from a set of species to determine the dominant environmental drivers of variation in species composition. We use data from 226 species from six regions of the world, and demonstrate the use of MARS for distribution modelling using presence-only data. We test whether (1) the type of data used to represent absence or background and (2) the signal from multiple species affect predictive performance, by evaluating predictions at completely independent sites where genuine presence–absence data were recorded. Models developed with absences inferred from the total set of presence-only sites for a biological group, and using simultaneous analysis of multiple species to inform the choice of predictor variables, performed better than models in which species were analysed singly, or in which pseudo-absences were drawn randomly from the study area. The methods are fast, relatively simple to understand, and useful for situations where data are limited. A tutorial is included.
1. Understanding factors that regulate the assembly of communities is a main focus of ecology. Human‐engineered habitats, such as reservoirs, may provide insight into these assembly processes because they represent novel habitats that are subjected to colonization by fishes from the surrounding river basin or transported by humans. By contrasting community similarity within and among reservoirs from different drainage basins to nearby stream communities, we can test the relative constraints of reservoir habitats and regional species pools in determining species composition of reservoirs.
2. We used a large spatial database that included intensive collections from 143 stream and 28 reservoir sites within three major river basins in the Great Plains, U.S.A., to compare patterns of species diversity and community structure between streams and reservoirs and to characterize variation in fish community structure within and among major drainage basins. We expected reservoir fish faunas to reflect the regional species pool, but would be more homogeneous that stream communities because similar species are stocked and thrive in reservoirs (e.g. planktivores and piscivores), and they lack obligate stream organisms that are not shared among regional species pools.
3. We found that fish communities from reservoirs were a subset of fishes collected from streams and dominant taxa had ecological traits that would be favoured in lentic environments. Although there were regional differences in reservoir fish communities, species richness, patterns of rank abundance and community structure in reservoir communities were more homogonous across three major drainage basins than for stream communities.
4. The general pattern of convergence of reservoir fish community structure suggests their assembly is constrained by local factors such as habitat and biotic interactions, and facilitated by the introduction of species among basins. Because there is a reciprocal transfer of biota between reservoirs and streams, understanding factors structuring both habitats is necessary to evaluate the long‐term dynamics of impounded river networks.
Aim The level of imperilment of mediterranean freshwater fish is among the highest recorded for any group of organisms evaluated to date. Here, we describe the geographical patterns in the incidence of threats affecting mediterranean freshwater fish and test whether the effects of specific threats are spatially related to the degree of imperilment of fish faunas.
Location The Mediterranean Basin Biome.
Methods From the IUCN Red List, we recorded the six main threats to 232 endemic freshwater fish species. We used data on fish distributions from IUCN to characterize the spatial patterns in the incidence of threats (as percentage of species affected) through multivariate statistics. We studied the relationships between threat incidence and two estimators of imperilment (proportion of species threatened and an index of extinction risk) at two spatial scales (10 × 10 km and basins) using partial least squares regressions (PLSR) that incorporated the effects of species richness and mean range size.
Results The main axis of variation in the incidence of threats to freshwater fish split areas mainly affected by invasive species from those areas where species are threatened by pollution and agriculture. Wherever invasive species and water extraction were predominant threats, fish assemblages consistently tended to be more imperilled.
Main conclusions As far as we know, this is the first large-scale analysis on the spatial relationships between the incidence of threats and level of imperilment of any taxonomic group. Our results highlight the primary role of invasive species and water extraction as drivers of native fish declines in the Mediterranean Basin. Large-scale patterns described here should be generated by local-scale impacts of both threats on fish biodiversity, widely reported in Mediterranean areas. Because all the species under concern are endemic, control of invasive species and reducing overexploitation of freshwater resources should be conservation priorities for mediterranean freshwater systems.
1. The ability of many introduced fish species to thrive in degraded aquatic habitats and their potential to impact on aquatic ecosystem structure and function suggest that introduced fish may represent both a symptom and a cause of decline in river health and the integrity of native aquatic communities.
2. The varying sensitivities of many commonly introduced fish species to degraded stream conditions, the mechanism and reason for their introduction and the differential susceptibility of local stream habitats to invasion because of the environmental and biological characteristics of the receiving water body, are all confounding factors that may obscure the interpretation of patterns of introduced fish species distribution and abundance and therefore their reliability as indicators of river health.
3. In the present study, we address the question of whether alien fish (i.e. those species introduced from other countries) are a reliable indicator of the health of streams and rivers in south-eastern Queensland, Australia. We examine the relationships of alien fish species distributions and indices of abundance and biomass with the natural environmental features, the biotic characteristics of the local native fish assemblages and indicators of anthropogenic disturbance at a large number of sites subject to varying sources and intensities of human impact.
4. Alien fish species were found to be widespread and often abundant in south-eastern Queensland rivers and streams, and the five species collected were considered to be relatively tolerant to river degradation, making them good candidate indicators of river health. Variation in alien species indices was unrelated to the size of the study sites, the sampling effort expended or natural environmental gradients. The biological resistance of the native fish fauna was not concluded to be an important factor mediating invasion success by alien species. Variation in alien fish indices was, however, strongly related to indicators of disturbance intensity describing local in-stream habitat and riparian degradation, water quality and surrounding land use, particularly the amount of urban development in the catchment.
5. Potential confounding factors that may influence the likelihood of introduction and successful establishment of an alien species and the implications of these factors for river bioassessment are discussed. We conclude that the potentially strong impact that many alien fish species can have on the biological integrity of natural aquatic ecosystems, together with their potential to be used as an initial basis to find out other forms of human disturbance impacts, suggest that some alien species (particularly species from the family Poeciliidae) can represent a reliable ‘first cut’ indicator of river health.
There is general agreement among scientists that biodiversity is under assault on a global basis and that species are being lost at a greatly enhanced rate. This article examines the role played by biogeographical science in the emergence of conservation guidance and makes the case for the recognition of Conservation Biogeography as a key subfield of conservation biology delimited as: the application of biogeographical principles, theories, and analyses, being those concerned with the distributional dynamics of taxa individually and collectively, to problems concerning the conservation of biodiversity. Conservation biogeography thus encompasses both a substantial body of theory and analysis, and some of the most prominent planning frameworks used in conservation. Considerable advances in conservation guidelines have been made over the last few decades by applying biogeographical methods and principles. Herein we provide a critical review focussed on the sensitivity to assumptions inherent in the applications we examine. In particular, we focus on four inter-related factors: (i) scale dependency (both spatial and temporal); (ii) inadequacies in taxonomic and distributional data (the so-called Linnean and Wallacean shortfalls); (iii) effects of model structure and parameterisation; and (iv) inadequacies of theory. These generic problems are illustrated by reference to studies ranging from the application of historical biogeography, through island biogeography, and complementarity analyses to bioclimatic envelope modelling. There is a great deal of uncertainty inherent in predictive analyses in conservation biogeography and this area in particular presents considerable challenges.
Abstract – The accuracy of bioassessment programmes is highly limited by the precision of the systems used to derive sensitivity–tolerance values for the organisms used as indicators. We provide quantitative support to the objective evaluation of freshwater fish species sensitivity to different sources of disturbance, accounting for co-variation issues not only between perturbations and natural gradients (especially river size), but also between different perturbations. With this aim, we performed two different principal component analyses: (i) on a general environmental matrix to obtain a perturbation gradient independent of river size effects and (ii) on human impairment-related variables to extract independent synthetic perturbation gradients. Then, we checked each species responses to those gradients to assess their sensitivity–tolerance through an available-used chi-squared analysis in the first approach and through a t-test/ancova analysis in the second one. In this way, we obtained sensitivity–tolerance which could be included in future bioassessment tools, enabling effective evaluations.
A basin approximation was used to analyse distribution patterns of different components of biodiversity (taxonomic richness, endemicity, taxonomic singularity, rarity) and conservation status of freshwater fish fauna in 27 Mediterranean Iberian rivers.
Basin area alone explained more than 80% of variation in native species richness. Larger basins featured not only a higher number of native species, but also more endemic and rare species and fewer diversified genera than smaller basins.
In contrast, smaller basins scored higher community conservation values, owing to their lower degree of invasion by introduced species.
The presence of dams was the most important factor determining the conservation status of fish communities, and it was also positively associated with the number of introduced species.
While the most important components of Iberian freshwater fish biodiversity are located in large basins, small unregulated basins feature better conserved fish communities.
Copyright © 2004 John Wiley & Sons, Ltd.
Reservoirs are important components of modern aquatic ecosystems that have negative impacts on native aquatic biota both up- and downstream. We used a landscape-scale geographic information system (GIS) approach to quantify the spatial effects of 19 large reservoirs on upstream prairie fish assemblages at 219 sites in Kansas, USA. We hypothesized that fish assemblage structure would vary with increasing distance from a reservoir and that the abundance of reservoir fishes in upstream reaches would decline with distance from a reservoir. Ordination of sample sites showed variation in fish assemblage structure occurred primarily across river basins and with stream size. Variance partitioning of a canonical ordination revealed that the pure effect of reservoir distance explained a small but significant (6%; F = 4.90, P = 0.002) amount of variability in fish assemblage structure in upstream reaches. Moreover, reservoir species catch per unit of effort (CPUE) significantly declined with distance from a reservoir, but only in fourth- and fifth- order streams (r2 = 0.32, P < 0.001 and r2 = 0.49, P < 0.001, respectively). Finally, a multivariate regression model including measures of stream size, catchment area, river basin, and reservoir distance successfully predicted CPUE of reservoir species at sites upstream of Kansas reservoirs (R2 = 0.45, P < 0.001). Overall, we found significant upstream effects of reservoirs on Kansas stream fish assemblages, which over time has led to a general homogenization of fish assemblages because of species introductions and extirpations. However, characteristic reservoir species are present throughout these systems and the importance of spatial proximity to reservoirs is probably dependent on the availability of suitable habitat (e.g. deep pools) in these tributary streams. Copyright © 2005 John Wiley & Sons, Ltd.
Most studies analyzing patterns in biotic homogenization of fish communities have used large-scale approaches, while the community-level
effects of species introductions and local extinctions within river basins have been sparsely analyzed. In this article, we
examine patterns in freshwater fish α- and β-diversity in relation to the presence of reservoirs in a Mediterranean river
(Guadiana river; Iberian Peninsula). We used fish samples from 182 river localities and 59 reservoir ones to address two main
questions: (i) do reservoirs favor the establishment of invasive fish species?; and (ii) do reservoirs bear taxonomically
homogenized fish communities? Although total species richness was not different between rivers and reservoirs, the latter
had more invasive species and less native ones. Fish species found in reservoirs tended to be larger ones, but invasive species
of any size showed higher preferences for reservoirs. Native species that were rare or absent in reservoirs were those that
showed higher sensitivity to invasive species in rivers. Reservoir fish communities were taxonomically homogenized in relation
to river ones, both when considering all fish species and using only natives or only invasive ones. Our results suggest that
invasive species occupying reservoirs constitute an ecological filter excluding most native species from such systems. Invasive
species in the study area are often widely introduced elsewhere, while native species found in reservoirs are congeneric and
ecologically similar to those found in other Iberian studies. Thus, we conclude that reservoirs promote taxonomic homogenization
at multiple spatial scales, while could also be promoting the functional homogenization of Iberian fish communities.
KeywordsBiotic homogenization–β-diversity–Freshwater fish–Fish conservation–Mediterranean rivers–Invasive species–Regulated rivers
Freshwater ecosystems are seriously imperiled by the spread of non-native fishes thus establishing profiles of their life-history
characteristics is an emerging tool for developing conservation and management strategies. We did a first approach to determine
characteristics of successful and failed non-native fishes in a Mediterranean-climate area, the Iberian Peninsula, for three
stages of the invasion process: establishment, spread and integration. Using general linear models, we established which characteristics
are most important for success at each invasion stage. Prior invasion success was a good predictor for all the stages of the
invasion process. Biological variables relevant for more than one invasion stage were maximum adult size and size of native
range. Despite these common variables, all models produced a different set of variables important for a successful invasion,
demonstrating that successful invaders have a combination of biological traits that may favor success at all invasion stages.
However, some differences were found in relation to published studies on fish invasions in other Mediterranean-climate areas,
suggesting that characteristics of the recipient ecosystem are as relevant as the characteristics of the invading species.
Predicting the distribution of endangered species from habitat data is frequently perceived to be a useful technique. Models that predict the presence or absence of a species are normally judged by the number of prediction errors. These may be of two types: false positives and false negatives. Many of the prediction errors can be traced to ecological processes such as unsaturated habitat and species interactions. Consequently, if prediction errors are not placed in an ecological context the results of the model may be misleading. The simplest, and most widely used, measure of prediction accuracy is the number of correctly classified cases. There are other measures of prediction success that may be more appropriate. Strategies for assessing the causes and costs of these errors are discussed. A range of techniques for measuring error in presence/absence models, including some that are seldom used by ecologists (e.g. ROC plots and cost matrices), are described. A new approach to estimating prediction error, which is based on the spatial characteristics of the errors, is proposed. Thirteen recommendations are made to enable the objective selection of an error assessment technique for ecological presence/absence models.
Analysis of Ordinal Categorical Data Alan Agresti Statistical Science Now has its first coordinated manual of methods for analyzing ordered categorical data. This book discusses specialized models that, unlike standard methods underlying nominal categorical data, efficiently use the information on ordering. It begins with an introduction to basic descriptive and inferential methods for categorical data, and then gives thorough coverage of the most current developments, such as loglinear and logit models for ordinal data. Special emphasis is placed on interpretation and application of methods and contains an integrated comparison of the available strategies for analyzing ordinal data. This is a case study work with illuminating examples taken from across the wide spectrum of ordinal categorical applications. 1984 (0 471-89055-3) 287 pp. Regression Diagnostics Identifying Influential Data and Sources of Collinearity David A. Belsley, Edwin Kuh and Roy E. Welsch This book provides the practicing statistician and econometrician with new tools for assessing the quality and reliability of regression estimates. Diagnostic techniques are developed that aid in the systematic location of data points that are either unusual or inordinately influential; measure the presence and intensity of collinear relations among the regression data and help to identify the variables involved in each; and pinpoint the estimated coefficients that are potentially most adversely affected. The primary emphasis of these contributions is on diagnostics, but suggestions for remedial action are given and illustrated. 1980 (0 471-05856-4) 292 pp. Applied Regression Analysis Second Edition Norman Draper and Harry Smith Featuring a significant expansion of material reflecting recent advances, here is a complete and up-to-date introduction to the fundamentals of regression analysis, focusing on understanding the latest concepts and applications of these methods. The authors thoroughly explore the fitting and checking of both linear and nonlinear regression models, using small or large data sets and pocket or high-speed computing equipment. Features added to this Second Edition include the practical implications of linear regression; the Durbin-Watson test for serial correlation; families of transformations; inverse, ridge, latent root and robust regression; and nonlinear growth models. Includes many new exercises and worked examples.
1. Relationships between probabilities of occurrence for fifteen diadromous fish species and environmental variables characterising their habitat in fluvial waters were explored using an extensive collection of distributional data from New Zealand rivers and streams. Environmental predictors were chosen for their likely functional relevance, and included variables describing conditions in the stream segment where sampling occurred, downstream factors affecting the ability of fish to move upriver from the sea, and upstream, catchment‐scale factors mostly affecting variation in river flows.
2. Analyses were performed using multivariate adaptive regression splines (MARS), a technique that uses piece‐wise linear segments to describe non‐linear relationships between species and environmental variables. All species were analysed using an option that allows simultaneous analysis of community data to identify the combination of environmental variables best able to predict the occurrence of the component species. Model discrimination was assessed for each species using the area under the receiver operating characteristic curve (ROC) statistic, calculated using a bootstrap procedure that estimates performance when predictions are made to independent data.
3. Environmental predictors having the strongest overall relationships with probabilities of occurrence included distance from the sea, stream size, summer temperature, and catchment‐scale drivers of variation in stream flow. Many species were also sensitive to variation in either the average and/or maximum downstream slope, and riparian shade was an important predictor for some species.
4. Analysis results were imported into a Geographic Information System where they were combined with extensive environmental data, allowing spatially explicit predictions of probabilities of occurrence by species to be made for New Zealand's entire river network. This information will provide a valuable context for future conservation management in New Zealand's rivers and streams.
Declining trends in the integrity of freshwater systems demand exploration of all possible conservation solutions. Freshwater protected areas have received little attention, despite the prominence of protected areas as conservation interventions for terrestrial and more recently marine features. We argue that a dialogue on freshwater protected areas has been neglected both because few models of good protected area design exist, and because traditional notions of protected areas translate imperfectly to the freshwater realm. Partly as a result of this conceptual disconnect, freshwaters have been largely ignored in protected area accounting schemes, even though a number of existing freshwater conservation strategies could qualify according to general protected area definitions. Rather than impose terrestrially-motivated ideas about protected areas onto freshwaters, we propose new vocabulary – freshwater focal area, critical management zone, and catchment management zone – that can be used in conjunction with IUCN protected area categories and that recognize the special ecological dynamics of freshwaters, and in particular the critical role of fluvial processes. These terms, which attempt to diffuse concerns about locking away essential ecosystem goods and services, move us toward consideration of protected areas for freshwaters. This conceptual shift, which acknowledges that freshwater conservation may occur remotely from freshwater features, opens the door for improved integration of freshwater, terrestrial, and marine concerns in protected area design and management.