All over the world, islands are suffering catastrophic declines in animal and plant species, directly or indirectly from humanity’s influence. Strangely, however, in Hawaii, the islands were experiencing local extinctions long before humans turned up, according to a study in Nature that attributes the decline to the older islands’ loss of land area.
Hawaii is famous for being created by a volcanic hotspot. Lava built up the islands directly above the spot, but they started to subside and erode once the spot had moved relative to the Earth’s crust. Today only the Big Island is still growing.
“The older islands were all much larger than they are now, and it looks like the flora and fauna filled up the ecological space fast enough that once the islands began to contract the crowding generated drove species to extinction,” said Professor Charles Marshall of the University of California, Berkeley in a statement.
The oldest Hawaiian islands are only a little over 6 million years old, and inevitably it took time for many species to reach such a remote location. Once birds, plants, and insects colonized Kauai, the first island, life jumped quickly across narrow channels to newer bits of land as they poked out of the sea.
Species lucky enough to reach Kauai found a paradise, free from their predators and competitors elsewhere. Colonizing species quickly diversified to fill available niches.
Eventually, however, these Edens became less idyllic as the inhabitants literally lost the ground from beneath their feet, with the loss of land forcing neighbors to compete for territory.
Estimates of the growth and decline of each of Hawaii’s islands. Lim and Marshall/Nature