Disentangling the drivers of continental mammalian endemism

Abstract

Endemic species and species with small ranges are ecologically and evolutionarily distinct and are vulnerable to extinction. Determining which abiotic and biotic factors structure patterns of endemism on continents can advance our understanding of global biogeographic processes, but spatial patterns of mammalian endemismhave not yet been effectively predicted and reconstructed. Using novel null model techniques, we reconstruct trends in mammalian endemism and describe the isolated and combined effects of physiographic, ecological, and evolutionary factors on endemism. We calculated weighted endemism for global continental ecoregions and compared the spatial distribution of endemism to niche-based, geographic null models of endemism. These null models distribute species randomly across continents, simulating their range sizes from their degree of climatic specialization. They isolate the effects of physiography (topography and climate) and species richness on endemism. We then ran linear and structural models to determine how topography and historical climate stability influence endemism. The highest rates of mammalian endemism were found in topographically rough, climatically stable ecoregions with many species. The null model that isolated physiography did not closely approximate the observed distribution of endemism (r 2 = .09), whereas the null model that incorporated both physiography and species richness did (r 2 = .59). The linear models demonstrate that topography and climatic stability both influenced endemism values, but that average climatic niche breadth was not highly correlated with endemism.Climate stability and topography both influence weighted endemism in mammals, but the spatial distribution of mammalian endemism is driven by a combination of physiography and species richness. Despite its relationship to individual range size, average climate niche breadth has only a weak influence on endemism. The results highlight the importance of historical biogeographic processes (e.g. centers of speciation) and geography in driving endemism patterns, and disentangle the mechanisms structuring species ranges worldwide.

Patterns of species richness and turnover in endemic amphibians of the Guineo‐Congolian rain forest

“…Our results are consistent with previous studies that have identified montane regions as areas of high vertebrate species richness and endemism (e.g. Kafash et al, 2020; Rahbek et al, 2019; Shipley & McGuire, 2023). The Nigeria‐Cameroon mountains consist of dense humid rain forests and deep gorges flanked by towering mountains (e.g.…”

The environmental conditions of endemism hotspots shape the functional traits of mammalian assemblages

“…Using WWF ecoregions for this study allowed us to divide the global community of mammals into assemblages of species that are likely to interact with each other and be influenced by similar ecological and physiographic processes, in contrast to other, arbitrary study units [12,51,52]. Ecoregions vary widely in size, but ecoregion area has little effect on mammalian endemism patterns not already explained by species richness patterns [13].…”

“…The abiotic, environmental pattern of vertebrate endemism on continental scales is well studied [13][14][15][16][17]. However, the biological mechanisms underlying the global pattern of endemism is still unclear, and little consensus has been reached on how the biotic, functional traits of vertebrate species within endemism hotspots might covary with this pattern [15,18,19].…”

“…By contrast, mammal species living in stable climates (through time and across seasons) and tropical regions are often 'packed' into trait space, with strong environmental filtering, niche partitioning and slow trait evolution [37,46]. Climate stability and species richness are integral drivers of mammalian endemism [13,15]. Therefore, endemism hotspots may likewise have strong environmental filtering, leading to assemblages that are functionally clustered in trait space when compared to areas of lower endemism.…”

“…Although patterns of endemism are correlated with richness, endemism hotspots (areas of high endemism) are environmentally distinct from those of high species richness [11,12]. In particular, endemism hotspots have rougher topography and more stable climates over time than expected given the number of species in the hotspot [13].…”