Abstract

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.

Highlights

  • A fundamental goal of evolutionary biology and related disciplines is to understand why some clades have more species than others[1]

  • We explore the relationships between diversification rates and: (i) average species niche widths within clades, (ii) clade-level niche widths, (iii) absolute niche divergence among species within clades, (iv) rates of niche evolution within clades, (v) the mean position of the clade’s niche, and (vi) the geographic range area of the clade

  • Our results show that two measures of niche change among species within clades are each strongly related to diversification rates among mammal clades

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Summary

Introduction

A fundamental goal of evolutionary biology and related disciplines is to understand why some clades have more species than others[1]. Richness leads to wider clade niches, but only because a clade with more species should span more divergent climatic conditions due to sampling alone, all else being equal This hypothesis predicts a relationship between diversification rates and family-level niche width, and predicts that the levels of climatic niche divergence can be explained by sampling size alone (i.e. number of species). (H4), wider family-level niche width could be indirectly related to diversification rate via a positive relationship between family-level niche width and the geographic extent of clades Under this hypothesis, a larger geographic range area for a clade could lead to a larger range of climatic conditions experienced by its species, and the larger range area could more directly increase diversification rate by increasing the chances of allopatric speciation, or diminishing the probability of extinction[19,20,21,22]. The results were consistent with the hypothesis that diversification rates were strongly influenced by speciation linked to climatic niche divergence (H2)

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