A dwarf elephant the size of a Shetland pony once roamed the Mediterranean island of Cyprus. In the West Indies, a giant rat-like rodent tipped the scales at more than 180 kilograms, rivaling an American black bear.
They were examples of the "island effect," a rule in evolutionary biology describing how large-bodied species tend to downsize on islands while small-bodied species upsize. These island dwarfs and giants — a menagerie also including pint-sized hippos, buffaloes and wolves — have long faced an elevated extinction risk that, according to a new study, is intensifying, imperiling some of Earth's most unique creatures.
Focusing on island-dwelling mammals, researchers said on Thursday they examined 1,231 existing species and 350 extinct ones spanning the past 23 million years. Extinction risk was seen highest among species that underwent more extreme body size shifts compared to mainland relatives. And the arrival of people on the islands raised extinction rates more than tenfold.