Variations of niche breadth, range sizes, and geographic exclusion with bat species richness

Aim More species-rich communities are often assumed to contain more specialist species with narrower niches and smaller ranges. Stronger interspecific competition in species-rich communities is thought to be a key mechanism explaining these patterns. Yet, the relationship between richness and specialization has so far only been studied for a few taxa, and characterizing the effects of interspecific competition on species distributions is challenging. Here, we assess broad-scale relationships between niche breadth, range sizes, and geographic exclusion along richness gradients of bats. Location Eastern Mediterranean, Western Asia, and Central Asia. Taxon Bats (Chiroptera) Methods Based on a novel integrated species distribution modeling approach that combines occurrence information with expert range maps, we assessed how niche breadth and range sizes varied with species richness. In addition, by contrasting species’ potential and realized distributions in areas where species pairs overlap, we derive indicators of geographic exclusion to understand how potential interspecific competition is affecting range limits along richness gradients. Results and Main conclusions We found a non-linear association between niche breadth and richness, with the most specialized species occurring in species-poor regions and niche breadth peaking at intermediate richness. Despite a positive association of niche breadth and range sizes at the species level, range sizes in predicted bat communities declined continuously with species richness. In addition, patterns of geographic exclusion were linked to patterns of niche breadth, with species filling less of their potential range overlaps when overlapping species were more specialized. Our findings suggest that small range sizes in species-rich bat communities are better explained by the number of interacting species than by environmental specialization or stronger exclusion between individual species. More broadly, we show how integrated distribution modeling approaches can shed new light on the interplay of species richness, specialization, and community structure, and caution against generalizing relationships between richness and specialization across taxa and geographies.

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