A major goal of evolutionary biology is to understand why clades differ dramatically in species richness. A key to this challenge is to uncover the correlates of variation in diversification rate (speciation – extinction) among clades. Here, we explore the relationship between diversification rates and the climatic niches of species and clades among 92 families of terrestrial mammals. We use a time-calibrated molecular phylogeny of mammals and climatic data from 3335 species. We show that considerable variation in net diversification rates among mammal families is explained by niche divergence (59%) and rates of niche change (51%). Diversification rates in turn explain most variation in species richness among families (79%). Contrary to expectations, patterns of diversification are not explained by differences in geographic range areas of clades, nor by their climatic niche position (i.e. whether they are primarily tropical or temperate). Overall, these results suggest that speciation through climatic niche divergence may help drive large-scale patterns of diversification and richness. Our results help explain diversification patterns in a major clade of vertebrates, and suggest that similar underlying principles may explain the diversification of many terrestrial clades.

Disentangling the relative role of environmental filtering and spatial processes in driving metacommunity structure across mountainous regions remains challenging, as the way we quantify spatial connectivity in topographically and environmentally heterogeneous landscapes can influence our perception of which process predominates. More empirical data sets are required to account for taxon‐ and context‐dependency, but relevant research in understudied areas is often compromised by the taxonomic impediment. Here we used haplotype‐level community DNA metabarcoding, enabled by stringent filtering of amplicon sequence variants (ASVs), to characterize metacommunity structure of soil microarthropod assemblages across a mosaic of five forest habitats on the Troodos mountain range in Cyprus. We found similar β diversity patterns at ASV and species (OTU, operational taxonomic unit) levels, which pointed to a primary role of habitat filtering resulting in the existence of largely distinct metacommunities linked to different forest types. Within‐habitat turnover was correlated to topoclimatic heterogeneity, again emphasizing the role of environmental filtering. However, when integrating landscape matrix information for the highly fragmented Quercus alnifolia habitat, we also detected a major role of spatial isolation determined by patch connectivity, indicating that stochastic and niche‐based processes synergistically govern community assembly. Alpha diversity patterns varied between ASV and OTU levels, with OTU richness decreasing with elevation and ASV richness following a longitudinal gradient, potentially reflecting a decline of genetic diversity eastwards due to historical pressures. Our study demonstrates the utility of haplotype‐level community metabarcoding for characterizing metacommunity structure of complex assemblages and improving our understanding of biodiversity dynamics across mountainous landscapes worldwide.

The use of correlative analyses might be insufficient to understand the processes that control biodiversity, because the variables accounting for different hypotheses (e.g. current climate, past climate change, post-glacial dispersal limitation) are mutually correlated. We suggest here that, in order to gain insight, it could be useful to search for latitudinal thresholds that could provide information about qualitative changes in the way biodiversity varies in space. Such tipping points could inform about higher-level processes that are not reflected in correlative analyses. We test whether similar breakpoints in latitudinal beta-diversity patterns exist for different vertebrate groups with diverse life histories and dispersal abilities. In birds, bats and non-volant mammals we find breakpoints similar to those of amphibians. Differences in species composition are mainly due to species replacement from the equator to the breakpoint, but are dominated by nested species losses from the breakpoint to higher latitudes. Thus, marked thresholds discriminate two world regions where different processes appear to drive biodiversity.

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Aim We analyse the latitudinal variation of range shape, testing whether ranges at higher latitudes or of larger size tend to be elongated in an east–west direction, as expected from climatic niche constraints. Additionally, we assess whether poleward range limits are less stochastic than equatorward limits. Location Global; all terrestrial areas except Antarctica. Time period Contemporaneous. Major taxa studied Birds and mammals. Methods We quantified the shape of the distribution ranges of 10,057 species of birds and 5,411 species of mammals, and assessed the relationship of range shape with latitude and range size using generalized additive models. The observed pattern was compared with that predicted by a null model, in which species ranges were constrained only by the shape of the landmasses. Furthermore, we divided each range in two polygons and measured their separate perimeters, to compare the limits of the poleward and equatorward portions of each range. Results In terrestrial mammals and birds, only species living at higher latitudes in the Northern Hemisphere and with large range sizes have ranges that consistently tend to be elongated in an east–west direction. The difference between observed and null range shapes increases from the Southern Hemisphere and the tropics towards the north. The difference between equatorward and poleward semi‐perimeters was relevant only in the Southern Hemisphere, and it is probably explained by the shape of the continents. Main conclusions The existence of a latitudinal gradient in range shape is consistent with a different role of deterministic and stochastic processes in the tropics versus high latitudes. Specifically, the results are in line with a scenario in which tropical niche conservatism and relatively evolutionarily labile lower thermal tolerance increase the relevance of climate in determining range limits towards the poles, with stochastic factors (e.g., dispersal limitation) more relevant in shaping low‐latitude range limits.