Dyer, E; (2016) A global study of the distribution and richness of alien bird species. Doctoral thesis , UCL (University College London).

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Abstract

Alien species are a major component of human-induced environmental change, yet spatial and temporal variation in the drivers of their introduction, and their subsequent distribution and richness, are poorly understood. Here, I present a global analysis of the drivers of this variation for a major animal group, birds (Class Aves), using the newly-created Global Avian Invasions Atlas (GAVIA) database. GAVIA includes information on introduction successes and failures, enabling me to examine the effect of colonisation pressure (the number of species introduced) on alien bird distributions. A description of the GAVIA database is given in Chapter 2, with details on its scope and sources, data collation and validation, and the production of alien range maps. Chapter 3 focuses on the early stages of the invasion pathway, and shows that historical introductions tend to originate in Europe, were driven by the global movements of British colonialism, and involved species deemed useful. Modern introductions, in contrast, tend to originate in Southeast Asia and Africa, are driven by factors associated with wealth, and involve species found in the pet trade. Chapter 4 identifies colonisation pressure as the principal determinant of alien bird species richness at a global scale. Additional anthropogenic factors (residence time, distance to historic port) and environmental variables (temperature range, precipitation) also influence richness. Chapter 5 analyses the factors influencing alien geographic range size, with species achieving a larger alien range if they have been introduced more often, have a larger native range and a shorter residence time. Chapter 6 examines latitudinal patterns of alien species richness and range size, and the likelihood of failure relative to latitude and native range limits. Overall, I demonstrate that alien bird distributions are primarily driven by anthropogenic influences, and highlight in particular the importance of incorporating a measure of colonisation pressure into studies of invasion.

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