Evans, Thomas; (2018) Quantifying and categorising the environmental impacts of alien birds. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

We are faced with a rising tide of alien species introductions across the globe. Some of these species can have significant impacts on native biodiversity. Being able to identify those species that are likely to cause the most damage when introduced to new environments is crucial if we are to minimise the broad range of impacts that they may have. A protocol has recently been developed to quantify and categorise the environmental impacts of alien species: the Environmental Impact Classification for Alien Taxa (EICAT). In Chapter 2, I use EICAT to quantify and categorise the impacts of alien species for an entire taxonomic class (birds). In so doing, I generate the first, directly comparable global dataset on their environmental impacts. The assessment reveals that most alien birds have relatively minor impacts, but that some have population-level impacts that result in native species extirpations and extinctions. The EICAT assessment provides useful information on the ways in which alien birds can adversely affect the environment, and the types of species that have the most severe impacts. It also reveals that we do not have any data on the environmental impacts of over 70% of alien bird species globally: these species are classified as Data Deficient (DD) under EICAT. I use the data generated by the EICAT assessment to answer a number of outstanding questions regarding the environmental impacts of alien birds. In Chapter 3, I examine the factors that influence whether we have impact data for alien birds. I show that many species may be DD because they have minor impacts that do not attract scientific research, but that some species may be DD for reasons unrelated to the severity of their impacts. In Chapter 4, I identify the traits of alien birds that influence the severity of their environmental impacts, finding that widely distributed, generalist birds tend to have the most severe impacts. In Chapter 5, I identify the drivers of spatial variation in the severity of alien bird impacts, finding that factors relating to the duration and frequency of alien bird invasions are key in determining whether the impacts sustained by a region will be damaging. I also produce the first global maps displaying the impacts generated by alien species from an entire taxonomic class. These maps, and the data underpinning them, can be used to identify regions of the world susceptible to the impacts of alien birds. They may therefore assist in directing management interventions to regions where they are most needed.

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