Diversity and Diversification Across the Global Radiation of Extant Bats

Abstract

Diversity is not distributed equally across the tree of life. This fundamental observation is central to ecology and evolutionary biology, and spans both spatial and temporal scales. Species richness, for example, is unevenly distributed both within and across clades. Biodiversity is often spatially concentrated in the tropics, with lower richness in temperate biomes. Some clades are characterized by extremely high ecological and morphological diversity, while others remain static across geologic timescales. This dissertation highlights these patterns of diversity across extant bats, the Order Chiroptera, and seeks to understand the evolutionary processes of diversification that govern them. Chapter 1 serves as both an introduction to the major questions of the dissertation and an overview of extant bat diversity, and how it varies spatially, phylogenetically, and ecologically across the globe. In this chapter, I primarily focus on spatial variation in regional richness patterns, and on the major differences between temperate and tropical bat diversity. In Chapter 2, I assemble a species-level molecular phylogeny of the order that is time-calibrated with fossil data. Using this phylogeny, I infer speciation dynamics across the order, and find that despite the imbalances in species richness, speciation rates are relatively homogeneous. I only infer strong evidence for more rapid rates within the subfamily Stenodermatinae, a clade of Neotropical phyllostomid bats. In Chapter 3, I develop models to test whether bat species co-occurrence is constrained by relatedness or ecomorphological similarity. Contrary to theoretical predictions and results from other major clades, I find that neither of these metrics of divergence controls co-occurrence in sympatry across most bats and realms. The only exception is the Neotropical realm, where bat species are most likely to co-occur when they are the most ecomorphologically similar to one another. This potentially indicates that Neotropical bat communities and species pools, at broad regional scales, are sorted by filtering processes that cluster bats with similar ecologies together in space. For Chapters 4 and 5, I assess how ecology and morphology are linked in New World bats. Chapter 4 describes an open-access, X-ray computed microtomography database of bat skulls, and how this resource can be used by the broader scientific and educational community. Chapter 5 combines crania from that database with diet data across New World bats, and tests whether ecological and morphological evolution are correlated in this group. Surprisingly, I find that patterns of ecological, trophic evolution are largely decoupled from morphological evolution. There is considerable heterogeneity in how readily different clades transition among trophic guilds, yet cranial shape evolution is surprisingly homogeneous. This decoupled pattern is potentially driven by underestimated trophic plasticity and omnivory among noctilionoid bats, as well as high lability among bat crania. Finally, in Chapter 6, I conclude with a summary of our major findings, and some thoughts on ecological and macroevolutionary inference both within bats and across the tree of life.