Diversity, invasive species and extinctions in insular ecosystems

Summary1 Species invasions are a primary driver of species additions and deletions in ecosystems. Understanding the intricacies of invasions and their consequences is central to ecology and biodiversity conservation. Extinctions are rarely random and often are influenced by a suite of factors. 2 We explored abiotic and biotic factors that correlate with and help to provide proximate explanations for insular extinctions driven by invasive predators on islands off western Mexico. 3 A number of factors that were hypothesized a priori to explain the observed extinction patterns performed better than island size alone. Alternative prey available to invasive predators was negatively correlated with extinction, with twice the number of alternative prey species present on extinction‐free islands compared to islands with extinctions. Carrying capacity estimates of extant populations were 27 times that of extinct populations. 4 An aggregate model that included alternative prey, carrying capacity, and seasonal precipitation was the best performing model. Those factors, which are supported by theory and empirical evidence, are informative to conservation decision‐makers. 5 Synthesis and applications . Islands with small native mammals and no, or few, alternative prey species available to invasive predators should be prioritized for eradication. By focusing regionally on a specific threat, we provide a framework to practitioners that aids in prioritizing invasive predator eradications to halt insular extinctions.