More species-rich communities are often assumed to contain more specialist species, typically characterized by narrower niche breadths or 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 niches and distributions is challenging. Thus, it remains unclear how general richness-specialization relationships are. Here, we assess relationships between specialization and interspecific competition along richness gradients of bats across four understudied global biodiversity hotspots. Using a novel, integrated species distribution modeling approach that combines expert range maps and occurrence records of 49 bat species, we produced fine-scale distribution and species richness maps, allowing us to assess environmental niche breadth and range sizes. Further, contrasting potential ranges obtained from traditional distribution models with realized ranges obtained through the integration of expert ranges, we assessed range filling and derived indicators of geographic exclusion that characterize how interspecific competition is limiting species' ranges. Our results highlight that the narrowest niche breadths and strongest geographic exclusion occur in species-poor, not species-rich bat communities, in contrast to what was found for other taxa. While niche breadth peaked at intermediate richness, range sizes decreased continuously with richness. These findings show that increasing bat species richness is not closely linked to environmental specialization across the entire richness gradient and that decreasing range sizes in species-rich communities could be driven by the number of interacting species, rather than by environmental specialization or individually stronger interactions. Our study shows how innovative distribution modeling approaches can shed new light on the interplay of species richness, interspecific competition, and community structure. More generally, our findings caution against generalizing relationships between richness and specialization across taxa and geographies.

Theoretical and empirical studies have shown that species radiations are facilitated when a trait under divergent natural selection is also involved in sexual selection. It is yet unclear how quick and effective radiations are where sexual selection is unrelated to the ecological environment. We address this question using grasshopper species of the genus Chorthippus, which have evolved strong assortative mating while lacking noticeable eco-morphological divergence. Mitochondrial genomes suggest that the radiation is relatively recent, dating to the mid-Pleistocene, which leads to extensive incomplete lineage sorting throughout the mitochondrial and the nuclear genomes. Nuclear data show extremely low genomic differentiation among species, yet hybrids are absent in sympatric localities. Demographic analyses shed some light into these seemingly contradictory patterns. The estimated demographic model shows a long period of geographic isolation, followed by secondary contact and extensive introgression. This suggests that an initial period of geographic isolation might favor the coupling of male signaling and female preference, which currently maintains species boundaries in the face of long-term gene flow. More generally, these results suggest that sexual selection can lead to radiations without a primary role of divergent natural selection, resulting in cryptic species that are genetically, morphologically and ecologically similar, but otherwise behave mostly as good biological species.