The impact of competition on global-change induced range shifts in birds

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Many species of birds are currently undergoing rapid range shifts in response to human-induced changes. As their ranges change, species encounter new species with which they hadn't before coexisted. This PhD project will aim to fill crucial gaps in our understanding of the consequences of range dynamics, taking a macroecological approach to answer several open questions, such as:(1) How do novel species interactions impact the outcome of range expansions? As species' ranges expand, novel species assemblages emerge, and competition between species may influence the dynamics of range expansion events. For instance, interspecific competition can cause competitive exclusion, preventing species from successfully colonizing areas where species occupying similar niches are already established. In addition, the distributions of many animals are limited by territorial aggression with other species, and reproductive interference appears to limit coexistence and range expansion in numerous taxa. Yet, despite broad appreciation of the importance of species interactions in shaping species' ranges, the impact of species interactions on contemporary range expansion is largely unknown. (2) What is the relative importance of exploitative competition (i.e., competition for access to limiting resources) and interference competition (e.g., territorial aggression between species) in structuring novel assemblages? Although some research has focused on predicting how species will respond to competition for access to habitat and resources as ranges change, less is known about how species' social behaviours might influence range dynamics. For instance, a few studies show that territorial species are likely to be aggressive toward closely related species as their ranges expand, which may slow down the speed at which ranges might otherwise expand. Similarly, theory predicts that reproductive interference-wasteful reproductive interactions between species-should prevent hybridizing species from coexisting, so reproductive interactions between species may also slow down the speed of range expansions. Yet, the relative impact of these different forms of species interactions remains unknown.(3) How do abiotic factors such as climate change and land use interact with interspecific competition during range expansions? While it is clear that changes in climate and land use impact bird populations and range dynamics, it is less clear which factors play the largest role in determining the relative success and failure of range shifts.Despite broad appreciation for the importance of biotic interactions in shaping species' ranges, studies that identify a role for species interactions in influencing the rates or outcomes of range expansion are surprisingly rare. Therefore, this project is likely to yield several high impact publications.