Species Range Size Research Articles

The effect of topographic complexity on species range size estimation and its conservation implications: a subtle oversight

The effect of topographic complexity on species range size estimation and its conservation implications: a subtle oversight

Range expansions of sexual versus asexual organisms: Effects of reproductive assurance and migration load.

It is generally considered that sexual organisms show faster evolutionary adaptation than asexual organisms because sexuals can accumulate adaptive mutations through recombination. Yet, empirical evidence often shows that the geographic range size of sexual species is narrower than that of closely related asexual species, which may seem as if asexuals can adapt to more varied environments. Two potential explanations for this apparent contradiction considered by the existing theory are reproduction assurance and migration load. Here, we consider both reproductive assurance and migration load within a single model to comparatively examine their effects on range expansions of sexuals and asexuals across an environmental gradient. The model shows that higher dispersal propensity decreases sexuals' disadvantage in reproductive assurance while increasing their disadvantage in migration load. Moreover, lower mutation rate constrains adaptation more strongly in asexuals than in sexuals. Thus, high dispersal propensity and high mutation rates promote that asexuals have wider range sizes than sexuals. Intriguingly, our model reveals that sexuals can have wider geographic range sizes than asexuals under low dispersal propensity and low mutation rates, a pattern consistent with a few exceptional empirical cases. Combining reproductive assurance and migration load provides a useful perspective to better understand the relationships between species' mating systems and their geographic ranges.

Habitat and not topographic heterogeneity constrains the range sizes of African mammals

Aim The extinction risks of species are influenced by their geographical range sizes, as species with smaller ranges are more likely to go extinct following disturbance events. Theoretically, heterogeneous landscapes can maintain small-ranged species, because they facilitate the coexistence of taxa that are each constrained to distinct abiotic conditions. However, we do not fully understand whether this process is more attributable to variation in habitat types (habitat heterogeneity) or physical elevations (topographic heterogeneity) across landscapes. Here, we compare the influences of habitat versus topographic heterogeneity on mammalian range sizes in Africa. Location Africa. Taxon Mammalia. Methods We built a phylogenetic generalized least squares model to predict the range sizes of 1033 mammalian species from their functional traits and abiotic conditions. We assessed how the performance of the model changed when we incorporated measures of the local habitat and, separately, topographic heterogeneity that species experience. Results Habitat and topographic heterogeneity are weakly correlated across Africa (ρ = 0.14). Habitat heterogeneity is inversely related to range size (model coefficient = −0.88). Incorporating habitat heterogeneity significantly decreased the model's AICc, increased its likelihood and increased the proportion of variance that is explained in the range sizes of species. Conversely, topographic heterogeneity is not significantly related to range size and had no impact on the model's AICc, likelihood or predictive performance. This contrast between habitat and topographic heterogeneity is particularly prevalent in carnivorous mammalian clades. Results at multiple spatial resolutions differed minimally. Main Conclusions Our findings advance ecological theory by demonstrating that a landscape's variation in habitats, and not in elevations, relates inversely with mammalian range size and therefore facilitates the coexistence of small-ranged mammals. Conservation efforts in regions of high habitat heterogeneity will be critical to prevent extinctions in Africa's biodiverse mammalian species.

Global distribution and richness of terrestrial mammals in tidal marshes

AbstractAimUnderstanding the determinants of species distribution and richness is key to explaining global ecological patterns. We examined the current knowledge about terrestrial mammals in tidal marshes and evaluated whether species richness increased with the marsh surface area and/or with their proximity to the equator and whether species distribution ranges decreased with latitude.LocationGlobal.MethodsWe reviewed the existing literature on terrestrial mammals in tidal marshes. We examined their ecological characteristics (e.g. habitat specialists, native or alien), predicted their variation in species richness and range size along latitude, and explored factors, such as surface area, underlying the global patterns found.ResultsWe found 962 records, describing 125 mammalian species using tidal marshes worldwide, also including several alien species. Most species (95%) were not marsh specialized, and some (18%) were of conservation concern. There were information gaps in South America, Africa, Australia and Asia, and a lack of information about mammalian ecological roles worldwide. We found that species richness increased with surface area, and showed a bimodal pattern peaked between 40° and 50° latitude in each hemisphere. We found no relationship between latitude and species range size.Main conclusionsOur worldwide findings revealed a broader range of tidal marshes inhabited by terrestrial mammals, and higher values of species richness than previously reported. The bimodal pattern of species richness was consistent with the species–area hypothesis, but it also suggested that further studies of species distribution in relation to historical and environmental factors will yield significant insights about variables driving richness in tidal marshes. Despite terrestrial mammal ubiquitous distribution in these ecosystems, there are considerable geographic gaps as regards knowledge about their functional importance and the impact of alien species on tidal marsh functioning. Consequently, extending our research efforts is key to planning the conservation of these coastal ecosystems.

Robustness of Bergmann’s and Rapoport’s rules to different geographical range estimates in New World pit vipers

AbstractAimBergmann's and Rapoport's rules are two ecogeographical patterns that predict an increase in species body size and range size, respectively, with increasing latitudes. Here, we evaluated whether using different geographical range estimates affects the assessment of Bergmann's and Rapoport's rules at the cross‐species and assemblage levels in New World pit vipers.LocationNew World.TaxonNew World pit vipers (Crotalinae).MethodsWe estimated geographical ranges for 135 (i.e. ≈93%) Crotalinae species using ecological niche modelling (ENM) and expert maps and assessed alternative hypotheses that could account for Bergmann's and Rapoport's rules. We evaluated both rules using ‘cross‐species’ (i.e. species as units of observation) and ‘assemblage’ (i.e. sites/grid cells as units of observation) approaches. We used phylogenetic generalized least squares (PGLS) analyses and generalized least squares (GLS) analyses to account for phylogenetic and spatial autocorrelation that could affect the evaluation of these rules at the cross‐species and assemblage levels, respectively.ResultsExpert maps differed significantly from ENM ranges. The cross‐species approach was robust to these different range estimates when Bergmann's and Rapoport's rules were evaluated. The assemblage analyses were more vulnerable to different range estimates, where contrasting results were observed in the assessment of Bergmann's rule but not in the evaluation of Rapoport's rule.Main ConclusionsDifferent geographical range estimates affected mainly the assessment of ecogeographical rules at the assemblage level, whereas the cross‐species analyses were more robust. However, this increased susceptibility of the assemblage approach to different range estimates was only observed when evaluating Bergmann's rule. Thus, our findings suggest that ecogeographical rules can have different levels of sensitivity to different range estimates, which can especially affect the assemblage‐level assessment of these ecogeographical patterns.

Environmental correlates of body size influence range size and extinction risk: A global study in rodents

AbstractAimSpecies‐level traits, such as body and range sizes, are important correlates of extinction risk. However, both are often related and are driven by environmental factors. Here, we elucidated links between environmental factors, body size, range size and susceptibility to extinction, across the whole order of rodents.LocationGlobal.Time periodCurrent.Major taxa studiedRodents (order Rodentia).MethodsWe compiled an unprecedentedly large database of rodent morphology, phylogeny, range size, conservation status, global climate and normalized difference vegetation index (NDVI), comprising >86% of all described species. Using phylogenetic regressions, we initially explored the environmental factors driving body size. Next, we modelled the relationship between body size and range size. From this relationship, we computed and mapped (at the assemblage level) an index of relative range size, corresponding to the deviation from the expected range size of each species, given its body size. Finally, we tested whether relative range was correlated with the risk of extinction of the species derived from an assessment by the International Union for Conservation of Nature.ResultsWe found that, contrary to the expectations of Bergmann's rule, the body size of rodents was mostly influenced by variation in NDVI (rather than latitude/temperature). Body size, in turn, imposed a constraint on species range size, as evidenced by a triangular relationship that was segmented at the lower bound. The relative species range size derived from this relationship highlighted four geographical regions where rodents with small relative range were concentrated globally. We demonstrated that lower relative range size was associated with increased risk of extinction.Main conclusionsSpecies that, given their body size, are distributed across ranges that are smaller than expected have elevated extinction risk. Therefore, investigating the relationships between environmental drivers, body size and range size might help to detect species that could become threatened in the near future.

A latitudinal signal in the relationship between species geographic range size and climatic niche area

Species with broader niches may have the opportunity to occupy larger geographic areas, assuming no limitations on dispersal and a relatively homogeneous environmental space. Here, we use data on a large set of mammal (n = 1225), bird (n = 1829) and tree (n = 341) species to examine the 1) relationship between geographic range size and climatic niche area, 2) influence of species traits on species departures from this relationship and 3) sensitivity of these relationships to how species range size and climatic niche area are estimated. We find positive geographic range size–climatic niche area relationships for all taxa, with residual variation dependent on latitude, and differing from a null model for mammals and birds, but not for trees. Together, we provide support for this general macroecological relationship which is dependent on space, weakly influenced by species traits, and different enough from a null model to suggest that geographic and demographic processes are important.

Seed traits and phylogeny explain plants' geographic distribution

Abstract. Understanding the mechanisms that shape the geographic distribution of plant species is a central theme of biogeography. Although seed mass, seed dispersal mode and phylogeny have long been suspected to affect species distribution, the link between the sources of variation in these attributes and their effects on the distribution of seed plants are poorly documented. This study aims to quantify the joint effects of key seed traits and phylogeny on species distribution. We collected the seed mass and seed dispersal mode from 1426 species of seed plants representing 501 genera of 122 families and used 4 138 851 specimens to model species distributional range size. Phylogenetic generalized least-squares regression and variation partitioning were performed to estimate the effects of seed mass, seed dispersal mode and phylogeny on species distribution. We found that species distributional range size was significantly constrained by phylogeny. Seed mass and its intraspecific variation were also important in limiting species distribution, but their effects were different among species with different dispersal modes. Variation partitioning revealed that seed mass, seed mass variability, seed dispersal mode and phylogeny together explained 46.82 % of the variance in species range size. Although seed traits are not typically used to model the geographic distributions of seed plants, our study provides direct evidence showing seed mass, seed dispersal mode and phylogeny are important in explaining species geographic distribution. This finding underscores the necessity to include seed traits and the phylogenetic history of species in climate-based niche models for predicting the response of plant geographic distribution to climate change.

The agony of choice: Species richness and range size in the determination of hotspots for the conservation of phyllostomid bats

Area-based strategies for conservation include defining species richness and rarity hotspots. However, excluding vulnerable species (e.g., with restricted distribution and categorized as threatened), in establishing such hotspots may limit their representativeness, so the convenience of asserting them has been widely debated. To inform conservation assessments for the New World leaf-nosed bats (Chiroptera: Phyllostomidae), we identified hotspots based simultaneously on species richness and rarity of 214 species. We projected species range maps on a 0.5° × 0.5° longitude-latitude grid, from which we built a presence-absence matrix with 6951 sites. Using range-diversity plots, we described richness-rarity hotspots (sites with high species richness and presence of rare species) and poorness-rarity hotspots (with low species richness and presence of rare species). We assess the representativeness of the hotspots within established protected areas using the World Database on Protected Areas. The richness-rarity hotspot was located in the Andean zone from Peru to Panama within which 46 species of phyllostomid bats are distributed and 37% of its surface is protected. While the poorness-rarity hotspot was located in the northern region of Mexico and the Caribbean with 50 phyllostomid bats species and 19% of its surface protected. We hope that our analysis represents a relevant tool for the conservation of phyllostomid bats, which provide several ecosystem services and are currently facing different threats derived from anthropogenic activities.

Does regional species diversity resist biotic invasions?

The role of regional species diversity in large-scale species invasions has been largely controversial. On the one hand, it has been proposed that diversity may facilitate invasion (“diversity begets diversity”) because regions with higher diversity may indicate favorable conditions for many more species. On the other hand, high diversity may indicate high levels of niche occupation, thus making it more difficult for new species to invade. In the past, invasion biologists have evaluated how regional native and exotic richness are related. Here, we test whether the range size of exotic species may be constrained by regional native richness using plant data from three continental regions in the Northern Hemisphere, i.e., Europe, Eastern Asia, and North America. We found that regional native plant diversity is inversely related to the range size of exotic species. This result may be due to stronger species interactions such as competition in species-rich habitats that limit the establishment and spread of exotic species.

Fitness homeostasis across an experimental water gradient predicts species' geographic range and climatic breadth.

Species range sizes and realized niche breadths vary tremendously. Understanding the source of this variation has been a long-term aim in evolutionary ecology and is a major tool in efforts to ameliorate the impacts of changing climates on species distributions. Species ranges that span a large climatic envelope can be achieved by a collection of specialized genotypes locally adapted to a small range of conditions, by genotypes with stable fitness across variable environments, or a combination of these factors. We asked whether fitness expressed along a key niche axis, water availability, could explain a species' realized niche breadth, its geographic range and climate breadth, in 11 species from a clade of jewelflowers whose range sizes vary by two orders of magnitude. Specifically, we explored whether the range size of a species was related to the ability of genotypes (maternal families) to maintain fitness across a range of experimental water availabilities based on 30-year historical field precipitation regimes. We operationally characterized fitness homeostasis through the coefficient of variation in fitness of a genotype (family) across the experimental water gradient. We found that species with genotypes that had high fitness homeostasis, low variation in fitness over our treatments, had larger climatic niche breadth and geographic range in their field distributions. The result was robust to alternate measures of fitness homeostasis. Our results show that the fitness homeostasis of genotypes can be a major factor contributing to niche breadth and range size in this clade. Fitness homeostasis can buffer species from loss of genetic diversity and under changing climates, provides time for adaptation to future conditions.

On the relationship between species diversity and range size

AbstractAimWhat factors may affect species range sizes remains a central question in ecology and biogeography. Particularly, whether and how species richness may regulate average species range size remains largely elusive. Here, we explore the relationship between species diversity and species range size at a global extent and discuss its implications and significance for ecology and management.LocationWorldwide.TaxonPlants and various groups of animals.MethodsWe used published data on plant richness and range size from around the world and synthesized related literature to assess the richness–range size relationships. We used paired t‐tests and spatial autoregressive models in data analyses. We conducted a series of partial regressions to partition the variation in species ranges explained by paired independent variables (i.e. species richness versus latitude, species richness versus temperature or species richness versus temperature variability).ResultsA negative relationship between species diversity (richness) and species range size is nearly ubiquitous. In most cases, species diversity was a better predictor for species range size than latitude, temperature or temperature variability.Main conclusionsThe diversity predictor works well for different taxonomic groups, regions, continents, and for both terrestrial and marine biomes. High species diversity could imply stronger species interactions such as competition which limit the range sizes of constituent species. A nearly universal negative richness–range size relationship thus has significant implications for species invasion biology and conservation.

Integration of hotspot identification, gap analysis, and niche modeling supports the conservation of Chinese threatened higher plants

AbstractA significant fraction of higher plants in China are threatened due to dramatic landscape transformation and increasing climate change. However, the conservation effectiveness of threatened higher plants (THPs) and their response to climate change are still underexplored to date. Based on the latest list of THPs in China, we obtained 102 593 occurrence records with latitude and longitude for 3858 THPs. By integrating the distribution patterns of three biodiversity indexes (i.e., species richness, species complementarity, and weighted endemism) and 10 plant categories, we identified hotspots for THPs and calculated the conservation effectiveness of nature reserves. We then selected 1959 THPs to project the shift of species richness and range sizes under climate change (representative concentration pathway [RCP] 2.6 and RCP 8.5). In total, 16 hotspot areas covering 7.38% of Chinese land area and containing 91.73% of THPs were identified. Current nature reserves protected 35.05% of hotspots, 73.07% of all THPs, and 56.64% of narrow‐ranged species. By the 2070s, the species richness of THPs were predicted to decrease in Southeast and Central China, and 42.42% (RCP 2.6) and 51.40% (RCP 8.5) of the 1959 THPs would confront habitat contraction. Future conservation efforts should focus on the conservation gaps and carry out targeted conservation for THPs with narrow distribution range. In order to cope with climate change, the hotspots with relatively low species loss can serve as important areas to contain current species diversity and the areas with high species gain offer opportunities for ex‐situ conservation of THPs.

Understanding the relationship between dispersal and range size.

The drivers of variability in species range sizes remain an outstanding enigma in ecology. The theoretical expectation of a positive dispersal-range size relationship has received mixed empirical support, despite dispersal being one of the most prominent hypothesised predictors of range size. Here, we synthesised results from 86 studies examining the dispersal-range size relationship for plants and animals in marine, terrestrial and freshwater realms. Overall, our meta-analysis showed that dispersal positively affects range size, but its effect is dependent on the clade and dispersal proxy studied. Moreover, despite potential differences in habitat connectivity, we did not find an effect of realm on the dispersal-range size relationship. Finally, the strength of the dispersal-range size relationship was dependent on latitude, range size metric and the taxonomic breadth of the study clade. Our synthesis emphasizes the importance of developing a mechanistic understanding of the trait to dispersal to range size relationship, considering the complexity of dispersal departure, transfer and settlement, as well as evolutionary components such as time for range expansion, speciation and past geological-environmental dynamics. We, therefore, call for a more integrative view of the dispersal process and its causal relationship with range size.

The Darwinian shortfall in plants: phylogenetic knowledge is driven by range size

The Darwinian shortfall, i.e. the lack of knowledge of phylogenetic relationships, significantly impedes our understanding of evolutionary drivers of global patterns of biodiversity. Spatial bias in the Darwinian shortfall, where phylogenetic knowledge in some regions is more complete than others, could undermine eco‐ and biogeographic inferences. Yet, spatial biases in phylogenetic knowledge for major groups – such as plants – remain poorly understood. Using data for 337 023 species (99.7%) of seed plants (Spermatophyta), we produced a global map of phylogenetic knowledge based on regional data and tested several potential drivers of the observed spatial variation. Regional phylogenetic knowledge was defined as the proportion of the regional seed plant flora represented in GenBank's nucleotide database with phylogenetically relevant data. We used simultaneous autoregressive models to explain variation in phylogenetic knowledge based on three biodiversity variables (species richness, range size and endemism) and six socioeconomic variables representing funding and accessibility. We compared observed patterns and relationships to established patterns of the Wallacean shortfall (the lack of knowledge of species distributions). We found that the Darwinian shortfall is strongly and significantly related to the macroecological distribution of species' range sizes. Small‐ranged species were significantly less likely to have phylogenetic data, leading to a concentration of the Darwinian shortfall in species‐rich, tropical countries where range sizes are small on average. Socioeconomic factors were less important, with significant but quantitatively small effects of accessibility and funding. In conclusion, reducing the Darwinian shortfall and smoothen its spatial bias will require increased efforts to sequence the world's small‐ranged (endemic) species.

Species range size shapes distance‐decay in community similarity

AbstractAim(i) To assess the dependence between the form of the decrease in biological similarity with distance (distance‐decay) and species range size and (ii) to introduce the use of a sigmoidal model, the Gompertz function, as a flexible alternative able to fit distance‐decay models under a wide variety of species range sizes.LocationApplicable worldwide.MethodsWe computed distance‐decay curves from simulated communities to assess how the species range sizes shape the functional form of distance‐decay patterns (i.e. negative exponential, power‐law or sigmoidal [Gompertz] relationships). Simulations were performed using different sample sizes and species detection probabilities. We also used distribution data of South American mammals to explore the relationship between species range size and the distance‐decay form in an empirical dataset.ResultsOur simulations showed that the power‐law is the best supported model when range sizes tend to be small. An increase in range sizes leads to a negative exponential relationship, taking the shape of a sigmoidal (Gompertz) relationship with the largest range size values. Similar results have been found in the distance‐decay pattern of South American mammals. Remarkably, the Gompertz function fits the data reasonably well in all scenarios.Main conclusionsThe functional form of distance‐decay patterns depends on a key biogeographical attribute: species range size. This dependence makes it an interesting tool to detect biodiversity threats associated with species range expansion, such as the biotic homogenization of faunas. The Gompertz function is the mathematical model that best accommodates different frequency distributions of species range size and, thus, allows cross‐taxa comparison of this biogeographical and ecological pattern.

Range-wide habitat use of the Harpy Eagle indicates four major tropical forest gaps in the Key Biodiversity Area network

Abstract Quantifying habitat use is important for understanding how animals meet their requirements for survival and provides information for conservation planning. Currently, assessments of range-wide habitat use that delimit species distributions are incomplete for many taxa. The Harpy Eagle (Harpia harpyja) is a raptor of conservation concern, widely distributed across Neotropical lowland forests, that currently faces threats from habitat loss and fragmentation. Here, we use penalized logistic regression to identify species-habitat associations and predict habitat suitability based on a new International Union for the Conservation of Nature range metric, termed Area of Habitat. From the species-habitat model, we performed a gap analysis to identify areas of high habitat suitability in regions with limited coverage in the key biodiversity area (KBA) network. Range-wide habitat use indicated that Harpy Eagles prefer areas of 70%–75% evergreen forest cover, low elevation, and high vegetation species richness. Conversely, Harpy Eagles avoid areas of >10% cultivated landcover and mosaic forest, and topographically complex areas. Our species-habitat model identified a large continuous area of potential habitat across the pan-Amazonia region, and a habitat corridor from the Chocó-Darién ecoregion of Colombia running north along the Caribbean coast of Central America. Little habitat was predicted across the Atlantic Forest biome, which is now severely degraded. The current KBA network covered 18% of medium to high Harpy Eagle habitat exceeding a target biodiversity area representation of 10%, based on species range size. Four major areas of high suitability habitat lacking coverage in the KBA network were identified in north and west Colombia, western Guyana, and north-west Brazil. We recommend these multiple gaps of habitat as new KBAs for strengthening the current KBA network. Modeled area of habitat estimates as described here is a useful tool for large-scale conservation planning and can be readily applied to many taxa.

Genetic evidence for post-glacial expansion from a southern refugium in the eastern moa (Emeus crassus).

Cycles of glacial expansion and contraction throughout the Pleistocene drove increases and decreases, respectively, in the geographical range and population size of many animal species. Genetic data have revealed that during glacial maxima the distribution of many Eurasian animals was restricted to small refugial areas, from which species expanded to reoccupy parts of their former range as the climate warmed. It has been suggested that the extinct eastern moa (Emeus crassus)-a large, flightless bird from New Zealand-behaved analogously during glacial maxima, possibly surviving only in a restricted area of lowland habitat in the southern South Island of New Zealand during the Last Glacial Maximum (LGM). However, previous studies have lacked the power and geographical sampling to explicitly test this hypothesis using genetic data. Here we analyse 46 ancient mitochondrial genomes from Late Pleistocene and Holocene bones of the eastern moa from across their post-LGM distribution. Our results are consistent with a post-LGM increase in the population size and genetic diversity of eastern moa. We also demonstrate that genetic diversity was higher in eastern moa from the southern extent of their range, supporting the hypothesis that they expanded from a single glacial refugium following the LGM.

Geographical range overlap networks and the macroecology of species co-occurrence.

Direct interactions among species are only possible if there is some overlap in their geographical distributions. However, despite intense focus of macroecological research on species geographical ranges, relatively little theoretical and empirical work has been done on the evolution of range overlap. In this study we explore a simple model of range overlap based on a log-normal distribution of species range sizes along a one-dimensional domain, with or without absorbing boundary conditions. In particular, we focus on the mean and variance of range overlap distributions, as well as the topology of the resulting overlap networks with respect to their degree distribution, evenness, and betweenness scores. According to the model, there is an approximately linear relationship between many aspects of the distribution of range overlaps and their underlying species distributions, such as their mean and variance. However, the expected mean number of non-zero range overlaps for a given species varied from linear to convex depending on the variance of the underlying geographical range distribution. The expected topology of range overlap networks varied substantially depending on the mean and variance in the corresponding geographical distributions, particularly in the case of the degree and closeness distributions. Finally, we test the expectations of our model against five datasets of altitudinal distributions of Neotropical birds. We found strong departures from the expectations based on our model, which could potentially result from phylogenetic niche conservatism related to altitudinal gradients in environmental conditions, or from the asymmetric colonization of mountains by species from lowlands. Potential applications of range overlap networks to a variety of ecological and evolutionary phenomena are discussed.

Trophic Niche Breadth of Falconidae Species Predicts Biomic Specialisation but Not Range Size

Simple SummaryThe diversity of food consumed and the habitats occupied by species and populations, which is called a trophic niche, play a key role in biogeographic distribution patterns. Niche narrowing is considered a strategy to reduce resource-use overlap and competition among coexisting individuals, populations or species. However, the success of narrowing (specialism) or broadening (generalism) the trophic niche seems to depend on the temporal and spatial predictability of food resources. It is thought that specialist strategies are favoured in homogeneous environments predictable in time and space, while environmental unpredictability promotes generalist strategies that, in turn, allow a greater capacity to colonise new niches, thus tending to increase the geographic range size. Interestingly, although known at a within-population scale, the relationship between diet breadth and environmental heterogeneity at global and interspecific scales has not been explicitly assessed. Using the family Falconidae (Aves, Falconiformes) as a model study, we tested the prediction that those species with a wider diet spectrum will have larger geographic range sizes and inhabit more biomes. Our findings show that trophic breadth was not a good predictor for range size but was for total environmental heterogeneity, with more diet-generalist species occupying a higher number of biomes.Trophic niche breadth plays a key role in biogeographic distribution patterns. Theory posits that generalist strategies are favoured in a more heterogeneous set of environments across a spatio-temporal gradient of resources predictability, conferring individuals and species a greater capacity for colonising new habitats and thus expanding their distribution area. Using the family Falconidae (Aves, Falconiformes) as a model study, we tested the prediction that those species with a wider diet spectrum will have larger geographic range sizes and inhabit more biomes. We assessed the relationships between trophic breadth (diet richness and diversity) at different taxonomic resolutions of the prey (class and order), range size and biomic specialisation index (BSI; number of biomes inhabited) for the different species. Despite different diet breadth indexes and taxonomic resolutions defined differently the trophic niche of the clade and species, our findings revealed that trophic breadth was not a good predictor for range size but was for total environmental heterogeneity, with more diet-generalist species occupying a higher number of biomes. Diet breadth at the order taxonomic level showed a higher capacity of predicting BSI than at class level, and can be an important ecological trait explaining biogeographic patterns of the species.