A global picture of biological invasion threat on islands

Abstract

Biological invasions are one of the main drivers of biodiversity losses. As threats from 39 biological invasions increase, one of the most urgent tasks is to identify areas of high 40 vulnerability. However, the lack of comprehensive information on the impacts of invasive 41 alien species (IAS) is especially a problem on islands, where most recorded extinctions 42 associated with IAS have occurred. Here we provide a global, network-oriented analysis of 43 IAS on islands. Using network analysis, we structured 27,081 islands and 437 threatened 44 vertebrates into 21 clusters, based on their profiles in term of invasiveness and shared 45 vulnerabilities. These islands are mainly located in the southern hemisphere and many are in 46 biodiversity hotspots. Some of them share similar characteristics regarding their connectivity 47 that could be useful in understanding their response to invasive species. The major invaders 48 found in these clusters of islands are feral cat, feral dog, pigs and rats. Our analyses reveal 49 those IAS that systematically act alone or in combination, and the pattern of shared IAS 50 among threatened species, providing new information to implement effective eradication 51 strategies. Combined with further local, contextual information this can contribute to global 52 strategies to deal with IAS. Islands harbour a significant portion of the Earth's species and have an unusually high rate of 64 endemism 1 . However, many species on islands are now recorded as threatened, and most 65 recorded extinctions of vertebrate species have occurred on islands 2 . Invasive alien species 66 (IAS) are considered the second most important driver of species extinctions on islands, and 67 are associated with nearly 25% of birds and amphibians currently threatened worldwide 3 . 68Island ecosystems are particularly vulnerable to biological invasions 2 . To date, there have 69 been over 700 attempted eradications of invasive alien mammals 4 , which have benefited to 70 600 local populations, leading to larger populations or increased distributional areas 4 . 71Specifically, 236 species have benefited from those eradication programs, including 62 72 species that are at risk of extinction, and four species had their extinction risk reduced as a 73 direct result of these eradications 4 . Despite these encouraging results, the threat posed by 74 invasive alien species (IAS) remains significant and widespread for native species 3 . Thus, 75 prioritization of research efforts and eradication strategies needs to be more effective 5 and 76 there are many more opportunities to decrease extinction risk for island species by eradicating 77 IAS. 78Because funding allocated to conservation is limited, it is important that these interventions 79 target islands where the conservation benefit will be highest. Efforts to prioritize research, 80 management, and policy for IAS have traditionally relied on expert judgments, and have been 81 limited to either single IAS 6 or subsets of islands 7,8 . In the absence of a systema...

Insights from modeling studies on how climate change affects invasive alien species geography

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