Extinction debt in naturally contracting mountain meadows in the Pacific Northwest,USA: varying responses of plants and feeding guilds of nocturnal moths

Fire suppression and climate change are leading to habitat fragmentation in temperate montane meadows across the globe, raising concerns about biodiversity loss. Restoration strategies may depend on the rate and nature of species response to habitat loss. We examined the effects of habitat loss and fragmentation on plants and nocturnal moths in natural montane meadows in the western Cascades, Oregon, USA, using generalized additive mixed models, non-metric multidimensional scaling, and multiple response permutation procedure. Historic (1949) rather than current (2005) meadow size explained species richness of herbaceous plants and herb-feeding moths and meadow plant community structure, indicating that loss of meadow species may be delayed by many decades following loss of meadow habitat, resulting in an extinction debt. In contrast, abundance of herb-feeding moths and species richness and abundance of woody plant-feeding moths were related to recent meadow configuration: as meadows are invaded by woody plants, abundance of meadow species declines, and woody plants and associated moths increase. Despite decades of fire suppression and climate change, montane meadows in many temperate mountain landscapes may still be amenable to restoration.     

Migration of moth species in a network of small islands

Rapidly increasing fragmentation of natural landscapes decreases the ability of many species to reach the smaller and more isolated patches of habitat in a metapopulation. The densities of local populations of several moth species and the butterfly Hipparchia semele in a network of small islands, and the rates of inter-island movement and movement patterns, were investigated, to determine the factors affecting the rate and pattern of movements. The estimated population densities ranged from 0.001 to 0.2 individuals/m². The observed emigration and immigration rates depended on island isolation and various traits of the species, with great variability in migration rates among species. Thin-bodied, slow-flying species did not move among the islands, whereas many robust, fast-flying species moved among the islands relatively frequently. Migration rate increased significantly with body size and was significantly higher in oligophagous than in polyphagous species, suggesting that these factors are important determinants of the migration rate of the species. Migration rate was low when the surface temperature of the sea was low, and a greater proportion of individuals emigrated from small than large patches of habitat. The migration distances of female noctuids were shorter than those of males and those of both sexes of the butterfly H. semele. The observed movement patterns are consistent with a metapopulation structure in most of the moth species.     

Ecological traits modulate bird species responses to forest fragmentation in an Amazonian anthropogenic archipelago

Aim

We assessed patterns of avian species loss and the role of morpho‐ecological traits in explaining species vulnerability to forest fragmentation in an anthropogenic island system. We also contrasted observed and detectability‐corrected estimates of island occupancy, which are often used to infer species vulnerability.

Location

Tucuruí Hydroelectric Reservoir, eastern Brazilian Amazonia.

Methods

We surveyed forest birds within 36 islands (3.4–2,551.5 ha) after 22 years of post‐isolation history. We applied species–area relationships to assess differential patterns of species loss among three data sets: all species, forest specialists and habitat generalists. After controlling for phylogenetic non‐independence, we used observed and detectability‐corrected estimates of island occupancy separately to build competing models as a function of species traits. The magnitude of the difference between these estimates of island occupancy was contrasted against species detectability.

Results

The rate of species loss as a function of island area reduction was higher for forest specialists than for habitat generalists. Accounting for the area effect, forest fragmentation did not affect the overall number of species regardless of the data set. Only the interactive model including natural abundance, habitat breadth and geographic range size was strongly supported for both estimates of island occupancy. For 30 species with detection probabilities below 30%, detectability‐corrected estimates were at least tenfold higher than those observed. Conversely, differences between estimates were negligible or non‐existent for all 31 species with detection probabilities exceeding 45.5%.

Main conclusions

Predicted decay of avian species richness induced by forest loss is affected by the degree of habitat specialisation of the species under consideration, and may be unrelated to forest fragmentation per se. Natural abundance was the main predictor of species island occupancy, although habitat breadth and geographic range size also played a role. We caution against using occupancy models for low‐detectability species, because overestimates of island occupancy reduce the power of species‐level predictions of vulnerability.

     

Explanations for bird species range size: ecological correlates and phylogenetic effects in the Canary Islands

Aim To explore the determinants of island occupancy of 48 terrestrial bird species in an oceanic archipelago, accounting for ecological components while controlling for phylogenetic effects. Location The seven main islands of the Canary archipelago. Methods We obtained field data on population density, habitat breadth and landscape distribution in Tenerife, Fuerteventura and La Palma, aiming to sample all available habitats and the gradient of altitudes. In total, 1715 line transects of 0.5 km were carried out during the breeding season. We also reviewed the literature for data on occupancy, the distance between the Canary Islands and the nearest distribution border on the mainland, body size and endemicity of the 48 terrestrial bird species studied. Phylogenetic eigenvector regression was used to quantify (and to control for) the amount of phylogenetic signal. Results The two measurements of occupancy (number of occupied islands or 10 × 10 km UTM squares) were tightly correlated and produced very similar results. The occupancy of the terrestrial birds of the Canary Islands during the breeding season had a very low phylogenetic effect. Species with broader habitat breadth, stronger preferences for urban environments, smaller body size, and a lower degree of endemicity had a broader geographical distribution in the archipelago, occupying a larger number of islands and 10 × 10 UTM squares. Main conclusions The habitat‐generalist species with a tolerance for novel urban environments tend to be present on more islands and to occupy a greater area, whereas large‐sized species that are genetically differentiated within the islands are less widespread. Therefore, some properties of the ranges of these species are explicable from basic biological features. A positive relationship of range size with local abundance, previously shown in continental studies, was not found, probably because it relies on free dispersal on continuous landmasses, which may not be applicable on oceanic islands.     

Metapopulations of moths on islands: a test of two contrasting models

1. We describe a generalized mainland-island metapopulation model which includes migration among the island populations. We test model predictions with quantitative data on more than 200 species of moths in two contrasting networks of small islands. The data include a direct measure of migration rate, based on trapping of moths on rocky skerries with no local populations of the vast majority of species.
2. We predicted that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, because the latter 'compete' for immigrants from the mainland. In contrast, we predicted that weakly flying species with potentially large local populations on the islands occur more frequently on islands in a group due to enhanced colonization rate.
3. Both predicted patterns were observed. Island occupancy increased significantly with the number of individuals caught on the rocky skerries, which is our measure of migration rate from the mainland, supporting the basic assumption that the species occur on the islands in a balance between colonizations and extinctions.
4. These results demonstrate that the moth metapopulations on islands represent a mixture of Levins's and mainland-island metapopulations, and that the mixture is different for different species in the same landscape.     

Dispersal and the interspecific abundance-occupancy relationship in British birds

Aim To test the prediction that deviations of species from the positive interspecific relationship between abundance and occupancy (a measure of geographical range size) are related to differences in dispersal. Location Great Britain. Methods Quantitative data on the abundances, occupancy and dispersal distances of British birds are compared using phylogenetic comparative methods. Results Measures of natal and adult dispersal distance, and the intraspecific variance in these parameters, explain little variation in occupancy in addition to that accounted for by population size. Individual dispersal variables failed to explain significant variance when added individually to a model with population size as a predictor. Migrants and species using wet habitats tend to disperse further than residents and dry habitat species. Analysing these four groups separately revealed effects of dispersal only on the occupancy attained by dry habitat species. Conclusions The only consistent predictor of occupancy in these analyses was population size.     

Finite metapopulation models with density-dependent migration and stochastic local dynamics

The effects of small density-dependent migration on the dynamics of a metapopulation are studied in a model with stochastic local dynamics. We use a diffusion approximation to study how changes in the migration rate and habitat occupancy affect the rates of local colonization and extinction. If the emigration rate increases or if the immigration rate decreases with local population size, a positive expected rate of change in habitat occupancy is found for a greater range of habitat occupancies than when the migration is density-independent. In contrast, the reverse patterns of density dependence in respective emigration and immigration reduce the range of habitat occupancies where the metapopulation will be viable. This occurs because density-dependent migration strongly influences both the establishment and rescue effects in the local dynamics of metapopulations.     

Estimating breeding season abundance of golden-cheeked warblers in Texas,USA

Population abundance estimates using predictive models are important for describing habitat use and responses to population-level impacts, evaluating conservation status of a species, and for establishing monitoring programs. The golden-cheeked warbler (Setophaga chrysoparia) is a neotropical migratory bird that was listed as federally endangered in 1990 because of threats related to loss and fragmentation of its woodland habitat. Since listing, abundance estimates for the species have mainly relied on localized population studies on public lands and qualitative-based methods. Our goal was to estimate breeding population size of male warblers using a predictive model based on metrics for patches of woodland habitat throughout the species' breeding range. We first conducted occupancy surveys to determine range-wide distribution. We then conducted standard point-count surveys on a subset of the initial sampling locations to estimate density of males. Mean observed patch-specific density was 0.23 males/ha (95% CI = 0.197–0.252, n = 301). We modeled the relationship between patch-specific density of males and woodland patch characteristics (size and landscape composition) and predicted patch occupancy. The probability of patch occupancy, derived from a model that used patch size and landscape composition as predictor variables while addressing effects of spatial relatedness, best predicted patch-specific density. We predicted patch-specific densities as a function of occupancy probability and estimated abundance of male warblers across 63,616 woodland patches accounting for 1.678 million ha of potential warbler habitat. Using a Monte Carlo simulation, our approach yielded a range-wide male warbler population estimate of 263,339 (95% CI: 223,927–302,620). Our results provide the first abundance estimate using habitat and count data from a sampling design focused on range-wide inference. Managers can use the resulting model as a tool to support conservation planning and guide recovery efforts. © 2012 The Wildlife Society.     

Demographic and spatial responses of resident bird populations to the arrival of migratory birds within an urban environment

Long-distance migration allows many bird species to overcome the severe climatic changes that occur in seasonal environments. Migration is highly demanding, and given its cyclical nature, we currently know that it has substantial effects on the population parameters of migratory birds during both breeding and wintering seasons. However, the potential effects of the presence of migratory birds in their wintering grounds on populations of resident birds have remain largely unexplored. Here, we propose the hypothesis that migratory birds negatively affect the habitat occupancy and population abundance of resident birds because of the arrival of numerous individuals during the most limiting months of the year. Here, we studied different species of migratory and resident birds that coexist during winter in an urban ecological reserve located within Mexico City. We used single-species multiseason occupancy models, two-species occupancy models, and distance sampling techniques to evaluate changes in occupancy and population density of resident bird species during three consecutive winters. We found an aggregation pattern between two resident species (Psaltriparus minimus and Thryomanes bewickii) with three migratory warblers (Cardellina pusilla, Setophaga coronata and Setophaga townsendi). Thus, our results provide evidence of the formation of mixed-species flocks in our study area. We also conclude that resident birds experience different demographic and behavioral processes during winter that not necessarily result from interspecific interactions with migratory birds.     

Contrasting effects of habitat quantity and quality on moth communities in fragmented landscapes

Habitat loss is commonly identified as a major threat to the loss of global biodiversity. In this study, we expand on our previous work by addressing the question of how lepidopteran species richness and composition vary among remnants of North American eastern deciduous forest located within agricultural or pastoral landscapes. Specifically, we tested the relative roles of habitat quantity (measured as stand area and percent forest in the greater landscape) and habitat quality (measured as tree species diversity) as determinants of moth species richness. We sampled >19 000 individuals comprising 493 moth species from 21 forest sites in two forested ecoregions. In the unglaciated Western Allegheny Plateau, the species richness of moths with woody host plants diminished as forest stand size and percent forest in the landscape decreased, but the total species richness and abundance of moths were unaffected by stand size, percent forest in the landscape, or tree species diversity. In contrast, the overall species richness and abundance of moths in the glaciated North Central Tillplain were affected primarily by tree species diversity and secondarily by forest size. Higher tree species diversity may reduce species loss from smaller forest stands, suggesting that small, diverse forests can support comparable numbers of species to those in less diverse, large stands. Smaller forests, however, contained a disproportionate number of moth species that possess larvae known to feed on herbaceous vegetation. Thus, although woody plant feeding moths are lost from forests with changes in stand area, new species appear capable of recolonizing smaller fragments from the surrounding habitat matrix. Our study further suggests that when species replacement occurs, local patch size and habitat quality may be more important than landscape context in determining the community structure of forest Lepidoptera.     

The effect of urbanization on the quality of remnant habitats for leaf-mining Lepidoptera on Quercus agrifolia

Previous studies suggest that urbanization alters the abundance and species richness of native insects on remnant habitat patches. However, the effects of urbanization on biological communities caused by habitat loss and fragmentation have not been separated from effects caused by altered habitat quality within remnant habitats or by the nature of the urban matrix. To test for an effect of urbanization acting via altered habitat quality or matrix characteristics, we controlled for the effects of habitat loss and fragmentation by comparing remnant habitat patches in urban and agricultural regions experiencing similar levels of habitat loss and fragmentation. We studied the species richness and abundance of the community of leaf-mining Lepidoptera on Quercus agrifolia in the San Francisco Bay Area. We measured the extent of five land-use types within a 500 m radius of each study patch. We built generalized linear models to determine if the extent of any of the landscape variables was associated with the species richness and abundance of the leaf-miner community. The extent of urbanization was not associated with species richness or total abundance. However, the abundance of three species of leaf-mining moths was associated with the extent of urbanization, but not in a consistent pattern. The abundances of Stigmella variella and Bucculatrix albertiella were higher and the abundance of Dryseriocrania auricyanea was lower at highly urbanized sites. The absence of a consistent association between urban land-use and both species richness and abundance indicates that the effects of urbanization on the community of leaf-mining moths of Q. agrifolia do not differ from the effects of replacing and fragmenting habitats with similar amounts of agricultural land-uses.     

Species traits predict island occupancy in noctuid moths

Knowing how species’ traits relate to processes that underlie occupancy patterns such as colonisation and population persistence, is important for our understanding of how species survive in fragmented and changing landscapes. We used automatic UV light-traps to sample noctuid moths on two remote islands, and compared traits of island occupants with those of a species pool from mainland southeast Sweden. Widely distributed species, generalist species, species with a long adult activity period and species active late in the summer had higher probability of occupancy on the remote islands. The results were consistent between islands. The traits of host plant specificity and species with an adult activity period during late summer remained robust and were statistically significant after controlling for any possible phylogenetic bias. This indicates that species exhibiting those traits survive better when habitat and climate changes. It is crucial to include our results in; (1) conservation planning, e.g. when devising conservation measures in fragmented landscapes; (2) for predictions of future occupancy patterns; and (3) ecosystem impact assessments, e.g. the importance of moths as pollinators, herbivores and being the functional link between parasitoids, plants, consumers and predators.     

Patch quality and context, but not patch number, drive multi-scale colonization dynamics in experimental aquatic landscapes

Colonization and extinction are primary drivers of local population dynamics, community structure, and spatial patterns of biological diversity. Existing paradigms of island biogeography, metapopulation biology, and metacommunity ecology, as well as habitat management and conservation biology based on those paradigms, emphasize patch size, number, and isolation as primary characteristics influencing colonization and extinction. Habitat selection theory suggests that patch quality could rival size, number, and isolation in determining rates of colonization and resulting community structure. We used naturally colonized experimental landscapes to address four issues: (a) how do colonizing aquatic beetles respond to variation in patch number, (b) how do they respond to variation in patch quality, (c) does patch context affect colonization dynamics, and (d) at what spatial scales do beetles respond to habitat variation? Increasing patch number had no effect on per patch colonization rates, while patch quality and context were critical in determining colonization rates and resulting patterns of abundance and species richness at multiple spatial scales. We graphically illustrate how variation in immigration rates driven by perceived predation risk (habitat quality) can further modify dynamics of the equilibrium theory of island biogeography beyond predator-driven effects on extinction rates. Our data support the importance of patch quality and context as primary determinants of colonization rate, occupancy, abundance, and resulting patterns of species richness, and reinforce the idea that management of metapopulations for species preservation, and metacommunities for local and regional diversity, should incorporate habitat quality into the predictive equation.     

Ontogenetic variation in density‐dependent growth of brown trout through habitat competition

1. Density‐dependent growth has been widely reported in freshwater fishes, but the ontogenetic evolution of competition and its subsequent effects on growth through a life span remains unclear. 2. Patterns of competition can be described by integrating population abundance data with habitat‐modelling results. Weighted usable area (WUA; m² WUA ha^?1) curves are obtained for each flow value and are then coupled with demographic data to obtain the occupancy rates (trout m^?2 WUA, the density of a given age class related to its suitable habitat) of the WUA for every age class, year and site. 3. We examined a long‐term data series searching for temporal variation in the influence of habitat occupancy rate on the growth of brown trout Salmo trutta. We tested whether (i) mean cohort mass (mean mass of the cohort during the first 3 years of life) is affected by the occupancy rate experienced across a life span; and (ii) the occupancy rate experienced at different ages influenced mean body size. 4. We observed a consistent negative power relationship between average cohort mass and mean occupancy rate through a life span, indicating that stronger cohorts were related to a reduced growth, with likely consequences for individual fitness. 5. The effects of occupancy rate on size‐at‐age were mainly detected in the size attained at the second year of life, but they were because of the competition at different times. Thus, the level of competition varied through ontogeny, in some of the rivers affecting growth since the first year of life, whereas in most of the rivers the main effects on body size resulted from the competition during the second year of life. 6. Occupancy rate appears more appropriate than density for assessing the occurrence of habitat competition in freshwater fishes, since it encompasses the differences in quantity and quality of suitable habitat for each age class. 7. Our study highlights the importance of density‐dependent growth as a key process in the dynamics of brown trout populations, its temporal variation depending on the temporal changes of density and the variation of competition associated with the habitat capacity for each life stage.     

Increased body size along urbanization gradients at both community and intraspecific level in macro‐moths

Urbanization involves a cocktail of human‐induced rapid environmental changes and is forecasted to gain further importance. Urban‐heat‐island effects result in increased metabolic costs expected to drive shifts towards smaller body sizes. However, urban environments are also characterized by strong habitat fragmentation, often selecting for dispersal phenotypes. Here, we investigate to what extent, and at which spatial scale(s), urbanization drives body size shifts in macro‐moths—an insect group characterized by positive size‐dispersal links—at both the community and intraspecific level. Using light and bait trapping as part of a replicated, spatially nested sampling design, we show that despite the observed urban warming of their woodland habitat, macro‐moth communities display considerable increases in community‐weighted mean body size because of stronger filtering against small species along urbanization gradients. Urbanization drives intraspecific shifts towards increased body size too, at least for a third of species analysed. These results indicate that urbanization drives shifts towards larger, and hence, more mobile species and individuals in order to mitigate low connectivity of ecological resources in urban settings. Macro‐moths are a key group within terrestrial ecosystems, and since body size is central to species interactions, such urbanization‐driven phenotypic change may impact urban ecosystem functioning, especially in terms of nocturnal pollination and food web dynamics. Although we show that urbanization's size‐biased filtering happens simultaneously and coherently at both the inter‐ and intraspecific level, we demonstrate that the impact at the community level is most pronounced at the 800 m radius scale, whereas species‐specific size increases happen at local and landscape scales (50–3,200 m radius), depending on the species. Hence, measures—such as creating and improving urban green infrastructure—to mitigate the effects of urbanization on body size will have to be implemented at multiple spatial scales in order to be most effective.     

Local and Regional Determinants of Colonisation-Extinction Dynamics of a Riparian Mainland-Island Root Vole Metapopulation

The role of local habitat geometry (habitat area and isolation) in predicting species distribution has become an increasingly more important issue, because habitat loss and fragmentation cause species range contraction and extinction. However, it has also become clear that other factors, in particular regional factors (environmental stochasticity and regional population dynamics), should be taken into account when predicting colonisation and extinction. In a live trapping study of a mainland-island metapopulation of the root vole (Microtus oeconomus) we found extensive occupancy dynamics across 15 riparian islands, but yet an overall balance between colonisation and extinction over 4 years. The 54 live trapping surveys conducted over 13 seasons revealed imperfect detection and proxies of population density had to be included in robust design, multi-season occupancy models to achieve unbiased rate estimates. Island colonisation probability was parsimoniously predicted by the multi-annual density fluctuations of the regional mainland population and local island habitat quality, while extinction probability was predicted by island population density and the level of the recent flooding events (the latter being the main regionalized disturbance regime in the study system). Island size and isolation had no additional predictive power and thus such local geometric habitat characteristics may be overrated as predictors of vole habitat occupancy relative to measures of local habitat quality. Our results suggest also that dynamic features of the larger region and/or the metapopulation as a whole, owing to spatially correlated environmental stochasticity and/or biotic interactions, may rule the colonisation – extinction dynamics of boreal vole metapopulations. Due to high capacities for dispersal and habitat tracking voles originating from large source populations can rapidly colonise remote and small high quality habitat patches and re-establish populations that have gone extinct due to demographic (small population size) and environmental stochasticity (e.g. extreme climate events).     

Testing the role of patch openness as a causal mechanism for apparent area sensitivity in a grassland specialist

Area sensitivity, species being disproportionately present on larger habitat patches, has been identified in many taxa. We propose that some apparently area-sensitive species are actually responding to how open a habitat patch is, rather than to patch size. We tested this hypothesis for Bobolinks (Dolichonyx oryzivorus) by comparing density and occupancy to a novel openness index, patch area, and edge effects. Bobolink density and occupancy showed significant relationships with openness, but logistic models based on an openness occupancy threshold had greater explanatory power. Thresholds remained approximately consistent from June through August, and shifted to be more open in September. Variance partitioning supported the openness index as unique and relevant. We found no relationships between measures of body condition (body mass, body size, circulating corticosterone levels) and either openness or area. Our findings have implications for studies of area sensitivity, especially with regards to inconsistencies reported within species: specifically, (1) whether or not a study finds a species to be area sensitive may depend on whether small, open sites were sampled, and (2) area regressions were sensitive to observed densities at the largest sites, suggesting that variation in these fields could lead to inconsistent area sensitivity responses. Responses to openness may be a consequence of habitat selection mediated by predator effects. Finally, openness measures may have applications for predicting effects of habitat management or development, such as adding wind turbines, in open habitat.     

Multilevel landscape utilization of the Siberian flying squirrel: Scale effects on species habitat use

Animals use and select habitat at multiple hierarchical levels and at different spatial scales within each level. Still, there is little knowledge on the scale effects at different spatial levels of species occupancy patterns. The objective of this study was to examine nonlinear effects and optimal‐scale landscape characteristics that affect occupancy of the Siberian flying squirrel, Pteromys volans, in South‐ and Mid‐Finland. We used presence–absence data (n = 10,032 plots of 9 ha) and novel approach to separate the effects on site‐, landscape‐, and regional‐level occupancy patterns. Our main results were: landscape variables predicted the placement of population patches at least twice as well as they predicted the occupancy of particular sites; the clear optimal value of preferred habitat cover for species landscape‐level abundance is a surprisingly low value (10% within a 4 km buffer); landscape metrics exert different effects on species occupancy and abundance in high versus low population density regions of our study area. We conclude that knowledge of regional variation in landscape utilization will be essential for successful conservation of the species. The results also support the view that large‐scale landscape variables have high predictive power in explaining species abundance. Our study demonstrates the complex response of species occurrence at different levels of population configuration on landscape structure. The study also highlights the need for data in large spatial scale to increase the precision of biodiversity mapping and prediction of future trends.     

Occupancy Patterns of Breeding American Black Ducks

Occupancy patterns can assist with the determination of habitat limitation during breeding or wintering periods and can help guide population and habitat management efforts. American black ducks (Anas rubripes; black ducks) are thought to be limited by habitat and food availability during the winter, but breeding sites may also limit the size or growth potential of the population. The Canadian Wildlife Service conducts an annual breeding waterfowl survey that we used to explore the hypothesis that black duck carrying capacity is limited by wetlands available for breeding in Québec, Canada. We applied single-visit, multi-species occupancy models to the 1990–2015 population survey data to determine if there was evidence the black duck population was limited by breeding habitat. Using a dynamic (multi-season) occupancy modeling approach, we estimated latent occupancy (occupancy accounting for imperfect detection) of black ducks and then used latent occupancy estimates to derive occupancy, colonization, and extirpation rates. We jointly modeled the occupancy dynamics of black ducks and other duck species in wetlands where both species were present. Throughout the duration of the survey, 44% of wetlands were never observed to be occupied by black ducks. Occupancy models showed wetland size was positively associated with occupancy at the first time step (initial occupancy) and colonization. All 2-species models indicated initial black duck occupancy, persistence (continued occupancy), and colonization were positively associated with the presence of a second species. Colonization rate over the 26-year period ranged from 7% to 27% across all models. Extirpation rates were similar and were constant through time within each model. Low occupancy rates, combined with approximately equal colonization and extirpation rates, suggest there are available wetlands for breeding black ducks in their core breeding area. If breeding habitats are not saturated, this suggests migration or wintering areas may be more limiting to black duck population abundance. © 2019 The Wildlife Society.     

Extensions of Island Biogeography Theory predict the scaling of functional trait composition with habitat area and isolation

The Theory of Island Biogeography (TIB) predicts how area and isolation influence species richness equilibrium on insular habitats. However, the TIB remains silent about functional trait composition and provides no information on the scaling of functional diversity with area, an observation that is now documented in many systems. To fill this gap, we develop a probabilistic approach to predict the distribution of a trait as a function of habitat area and isolation, extending the TIB beyond the traditional species–area relationship. We compare model predictions to the body‐size distribution of piscivorous and herbivorous fishes found on tropical reefs worldwide. We find that small and isolated reefs have a higher proportion of large‐sized species than large and connected reefs. We also find that knowledge of species body‐size and trophic position improves the predictions of fish occupancy on tropical reefs, supporting both the allometric and trophic theory of island biogeography. The integration of functional ecology to island biogeography is broadly applicable to any functional traits and provides a general probabilistic approach to study the scaling of trait distribution with habitat area and isolation.