UC Santa Cruz

Species and ecosystems worldwide are threatened by human activities, and intensive conservation efforts are needed to slow the ongoing biodiversity crisis (Tittensor et al. 2014). Islands are crucial to the conservation of global biodiversity: in just 5.5% of the earth's land area, they contain a disproportionate amount of terrestrial species, including an estimated 19% of birds and 17% of rodents. Islands are also highly vulnerable to human impact; 77% of known terrestrial vertebrate extinctions have taken place on islands and 40% of critically endangered species currently inhabit them (Tershy et al. In press). The leading cause of extinction and endangerment on islands is introduced species (Tershy et al. In press). In particular, animals associated with humans, such as such as rats, mice, pigs, goats, rabbits, and cats, have become feral on a large percentage of the world's roughly 400,000 islands (Atkinson 1985). These invaders have a myriad of direct and indirect effects on insular species, such as overgrazing of native plants, predation of native animals, competition with natives for food and other resources, and alteration of important physical and chemical ecosystem processes (Croll et al. 2005, Towns et al. 2006, Fukami et al. 2006, Kurle et al. 2008, Spear and Chown 2009, Simberloff 2011, Medina et al. 2011).

The eradication of invasive mammals from islands is an increasingly utilized conservation tool with a strong record of mitigating or reversing much of the damage caused by invasions (Barun et al. 2011a). Nearly 1,100 successful eradications to date have removed invasive mammals from 750 islands globally (DIISE 2014). Ongoing developments in eradication technologies are creating opportunities to eradicate invasive vertebrates from increasingly large and complex islands (Howald et al. 2007, Burbidge 2011, Campbell et al. 2011). Consequently, national and regional government agencies and conservation organizations are increasingly investing in vigorous eradication programs on islands. However, the global scale of island invasions greatly outweighs the resources available to undertake eradication projects. To ensure that biodiversity conservation resources are allocated as effectively and efficiently as possible, islands must be prioritized for eradications.

In my dissertation I address the island prioritization problem comprehensively. First, I develop a statistical model that explains global island extinctions as a function of invasive mammal presence, native taxonomy, and island attributes (Chapter 1). I use this model to isolate and quantify the impacts of invasive mammals on globally threatened island vertebrate species, and to predict the benefits to these species from invasive mammal eradication. Then, I combine these predicted benefits with eradication cost estimates, and develop an optimization model that identifies sets of islands where specified conservation goals can be attained via eradication for the minimum cost (Chapter 2). Finally, I assess the importance of socio-political factors in global conservation planning (Chapter 3). Taken together, the sections of my dissertation synthesize global data on island biodiversity, threats, costs, and governance, and provide results and tools that strengthen global prioritization efforts for invasive mammal eradications on islands.