Biotic interactions and the generation and organisation of biodiversity

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One of the biggest challenges facing biologists is to predict, and perhaps prevent, the loss of biodiversity. For some groups, such as birds and mammals, we know where species live and can identify biodiversity hotspots - areas of the world with unusually high numbers of species. But knowing where species live is not enough: to determine how biodiversity will be affected by global change we need to understand the evolutionary processes that generate it. Yet, species do not evolve in isolation: they evolve together in the context of communities or ecosystems. Consider two species that need the same limited resource. Can the two species co-exist? One might think not - they are in competition with one another and for one species to succeed then it must do so at the expense of the other. This may often be true, but an alternative is for one or both species to use the resource in different ways, or even to use a different resource altogether. The finches of the Galapagos Islands, made famous by Charles Darwin, reveal both of these outcomes of competition: where two species, the medium ground finch and the small ground finch, occur together on the same island they can be easily distinguished by differences in beak size, but on some islands one species is much reduced in number or even absent altogether and in such cases the two species typically have similar, intermediate, beak sizes. So the interactions between species in communities are important as drivers of evolutionary change and in determining which species live where. The aim of my research is to understand how interactions that act over generations within communities can influence the evolution of biodiversity over thousands to millions of years. Does competition cause evolution to speed up? Can changes in diversity through time in the fossil record be attributed to competition? My solution to understanding these problems is to build computer models that mimic competitive interactions and generate predictions of evolutionary change among competing species. This is an exciting approach because by mimicking a range of evolutionary scenarios we can generate predictions of how species change over long time-scales and how these changes alter biodiversity. More importantly, we can compare our predictions with real data from living and fossil species to test how different ecological processes determine how species and their traits diversify and which species live together. This is a major challenge as ecological communities contain multiple species and each species occurs in multiple communities. Not only that but the importance of species interactions is influenced by other factors. If there is ecological opportunity such as the chance to occupy a new habitat, then the pressures driving evolution will change. Ecological opportunity could arise due to environmental change, the evolution of a key innovation or a host of other factors. For example, a group of Caribbean lizards called anoles have diversified rapidly to occupy trees, partly due to the evolution of a unique toe-pad. This type of ecological opportunity may even lead to the formation of new species as different populations of the same parent species diverge from one another, as is the case for anoles. To prise apart the role of ecological opportunity and competition in generating biodiversity I explore variation and evolution in the morphology, ecology and behaviour in different groups of organisms. Hummingbirds are one such group. There are 330 hummingbird species that feed primarily on nectar, occupy diverse habitats across their geographic range, and display several feeding behaviours. In short, they provide an exceptional group to test the relative importance of competition and ecological opportunity in driving large-scale evolution change. By combining this real-world data with predictive models, I will provide new insight into how past and present-day biological diversity is generated and maintained.