Spatial and temporal signatures of ecological constraints on diversity

Abstract

Broad-scale diversity patterns are the outcome of ecological and evolutionary processes that permit different numbers of species to coexist in a region. Many studies have focused on understanding the factors that allow a region to contain more species or a clade to diversify more rapidly. In this thesis, I shift focus to instead explore the constraints that prevent biodiversity increasing unbounded, using a combination of phylogenetic and biogeographical approaches across a range of temporal and spatial scales. In chapter two, I investigate conservatism (i.e., the tendency for more closely related species to be more similar) in the extremes of climate tolerated by a species, assessing the hypothesis that tightly-conserved tolerances are influential in determining the range extents of the species. By using global data from two vertebrate classes and a range of climatic variables, I assess the taxonomic generality of this hypothesis and identify the most strongly conserved variables. In chapters three and four, I develop novel macroecological analyses of factors that may limit the extent of geographic ranges and apply them to Afrotropical birds (chapter three) and all continental mammals (chapter four). Chapter five assesses how the spatial distribution of range limits can be used to compare species’ relative abilities to occupy available landscape. In chapter six, I present new methods to detect signals of past changes to diversity limits in phylogenies, using simulations to explore the power of phylogenies to reveal such patterns of diversity-dependent cladogenesis. In addition to the main research chapters, I append a synthetic review, of which I am joint first author, exploring the evolutionary underpinnings of large-scale species-area relationships. This thesis builds links between the macroecology of species’ distributions with the dynamics of clades over macroevolutionary timescales to determine how geography, phylogeny and history interact in the generation and maintenance of large-scale biodiversity.