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.