Global threat exposure of islands in a changing world

Abstract

Islands are at the forefront of global environmental change. Biological invasions, land-use change, and climate change are driving population declines and causing irreversible losses in island ecosystems. Although global threat exposure maps have been developed in recent years, they are mostly designed for coarse-grained, continental-extent analyses, often overlooking islands. Here, we assessed the cumulative exposure to biological invasion, land-use change, and climate change by 2050, for more than 16,000 islands worldwide using multiple threat markers. Climate change emerged as a ubiquitous threat, being the dominant threat for 65% of all islands, followed by land-use change (22%) and biological invasions (13%). Islands with the highest cumulative exposure were more likely to be isolated, without historical connection with the mainland. Small and low-elevation islands at low latitudes exhibited greater exposure to climate change, whereas larger, high-elevation islands tended to be more exposed to land-use change. Certain countries and subdivisions, such as Seychelles, Bangladesh, China, French Polynesia, and Micronesia, harbored statistically disproportionate numbers of highly exposed islands, highlighting geographic hotspots of cumulative exposure where conservation efforts might be particularly urgent. Our study indicates that by 2050, most islands will be simultaneously exposed to a triple threat arising from the combined impacts of land-use change, climate change, and biological invasions. This study provides robust quantification of island cumulative exposure to three key drivers of biodiversity loss, making a crucial step toward assessing global biodiversity vulnerability.