The ecological and evolutionary drivers of spatial biodiversity patterns

Abstract

The form, function, and kinds of species that coexist together vary dramatically from place to place. These spatial patterns of biodiversity are the focus of biogeographical and macroecological research and offer us clues into the evolutionary processes shaping nature's variety. Finding general patterns and their underlying drivers, however, is not a straightforward task because a suite of ecological and evolutionary processes interact to shape patterns of biodiversity in the present-day. By integrating geographic, phylogenetic, phenotypic, and ecological data, and methods from the tool kits of community ecologists, macroevolutionists, and biogeographers, we can delve into the complexities shaping diversity patterns and get a more holistic understanding of their origin and maintenance.

In my opening chapter I briefly summarise the state of the field and introduce the outline of my thesis. The first two chapters forming the core of my thesis (Chapter Two and Chapter Three) present new methods to study spatial patterns of biodiversity. Chapter Two presents a process-based model of geographic range evolution and the geography of speciation. I use this model to make inferences about the history of speciation in thirty different plant and animal clades, highlighting some general taxonomic trends in speciation which have shaped biogeographic patterns in the present day. Then, in Chapter Three, I present a method to reconstruct temporal patterns in the evolution of biodiversity based on ancestral range estimates from historical biogeographic models.

The following three chapters present empirical studies which link community ecology, macroecology, and macroevolution to better understand spatial diversity patterns in plants and lizards. Chapter Four integrates phenotypic and spatial data to look at what drives global patterns of species richness in ten different lizard clades, comprising over 6000 species. Chapter 5 and Chapter 6 explicitly investigate links between community ecology and macroevolution to look at the evolution of the Southwest Australian Biodiversity Hotspot flora, using a large genus of Australian plants, Hakea (family Proteaceae), as a case study. Chapter Five focuses on how macroevolutionary dynamics have led to a greater concentration of diversity of Hakea in the Mediterranean-climate-ecosystem of Southwest Australia compared to other biomes. Chapter Six narrows in on the Southwest biodiversity hotspot asking how pollination ecology in Hakea has evolved in response to high diversity of closely related species.

Finally, I conclude by highlighting how the preceding chapters, which cover a broad range of topics, are intertwined in the aim of linking ecological and evolutionary processes to better understand spatial diversity patterns, all forming pieces of the same puzzle. I also briefly highlight future directions. Together, my thesis investigates the evolution of diversity using different approaches, united by the common goal of finding a better understanding of the patterns of diversity we appreciate in the world today.