Scientists' warning - The outstanding biodiversity of islands is in peril

Despite islands contributing only 6.7% of land surface area, they harbor similar to 20% of the Earth's biodiversity, but unfortunately also similar to 50% of the threatened species and 75% of the known extinctions since the European expansion around the globe. Due to their geological and geographic history and characteristics, islands act simultaneously as cradles of evolutionary diversity and museums of formerly widespread lineages-elements that permit islands to achieve an outstanding endemicity. Nevertheless, the majority of these endemic species are inherently vulnerable due to genetic and demographic factors linked with the way islands are colonized. Here, we stress the great variation of islands in their physical geography (area, isolation, altitude, latitude) and history (age, human colonization, human density). We provide examples of some of the most species rich and iconic insular radiations. Next, we analyze the natural vulnerability of the insular biota, linked to genetic and demographic factors as a result of founder events as well as the typically small population sizes of many island species. We note that, whereas evolution to-ward island syndromes (including size shifts, derived insular woodiness, altered dispersal ability , loss of defense traits, reduction in clutch size) might have improved the ability of species to thrive under natural conditions on islands, it has simultaneously made island biota disproportionately vulnerable to anthropogenic pressures such as habitat loss, overexploitation, invasive species, and climate change. This has led to the documented extinction of at least 800 insular species in the past 500 years, in addition to the many that had already gone extinct following the arrival of first human colonists on islands in prehistoric times. Finally, we summarize current scientific knowledge on the ongoing biodiversity loss on islands worldwide and express our serious concern that the current trajectory will continue to decimate the unique and irreplaceable natural heritage of the world's islands. We conclude that drastic actions are urgently needed to bend the curve of the alarming rates of island biodiversity loss.

Automated summary

Although islands only account for 6.7% of the Earth's land surface area, they harbor around 20% of the Earth's biodiversity and a disproportionately high percentage of threatened and extinct species. Islands act as both cradles for evolutionary diversity and museums of once widespread lineages, but their unique endemic species are often vulnerable due to genetic and demographic factors linked with colonization history. The vulnerability of island biota, exacerbated by anthropogenic pressures, has led to a significant number of extinctions in the past 500 years, with ongoing biodiversity loss posing a serious threat to the world's islands.