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Ecological and genetic responses of avifauna in species depauperate island ecosystems.

Norrey, John Daniel (2017) Ecological and genetic responses of avifauna in species depauperate island ecosystems. Doctoral thesis (PhD), Manchester Metropolitan University.


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Understanding patterns in species abundance, distribution, and assemblages is an important component of biogeographical ecology, species diversity, and conservation. Ecological release and the taxon cycle are two theories proposed to describe patterns in species distribution and abundance on islands. These interlinked theories attempt to explain what happens to species when they enter novel, species-depauperate island ecosystems and how they change and evolve over time and space. Developing our knowledge of these two processes is not only important to understanding the evolutionary history of taxa but could help us understand how invasive species respond to island environments, how species may respond under changing conditions of climate change, and species susceptibility to extinction. The aim of this study is to test for the presence of ecological release and the taxon cycle across Macaronesia. The thesis addresses criticisms of previous studies by using novel tools such as the availability of large-scale datasets of species distribution, biodiversity, and modern molecular tools to provide a temporal scale to the study and modern statistical techniques to model the taxon cycle and alternative models. Predictions associated with ecological release and the taxon cycle are tested across multiple island groups, species, and at different scales, using genetic, morphological, and ecological data, comparable species, habitats, and climates. The results identified a consistent trend in niche expansion and density compensation in many of the focal species across a number of islands compared to mainland populations, thus supporting the presence of ecological release. Density compensation was also found when examining published estimates of abundance across European islands. A significant non-linear relationship between species age, abundance, and distribution was found in the birds across Macaronesia. Models for both distribution and abundance show a complex, consistent pattern of increase then decrease with lineage age. Trends throughout the thesis supported the presence of the taxon cycle across the Macaronesian islands, with patterns of expansion in distribution and abundance (ecological release) in more recent, younger colonists and contraction in range, niche shift, and decrease in abundance in more established, older species. Both ecological release and the taxon cycle may be important to better understand species invasions, speciation, and susceptibility to extinction. However, further research is needed into the factors that drive these mechanisms and influence the magnitude in species responses.

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