Hawaii’s unique animal and plant diversity has been declining on all but the Big Island for millions of years, long before humans arrived, according to a new analysis of species diversity on the islands by the University of California, Berkeley, evolutionary biologists.
The team concluded that animal diversity of Hawaii have already decreased before human’s involvement in animal extinction. The shrinking areas of old islands
Today, all of the islands except the Big Island of Hawaii — the only island still growing — have experienced a decrease in species diversity, albeit imperceptibly on human time scales, since even before the extinction caused by human activity.
They reached this conclusion with a new method for analyzing the species diversity on the different islands in the multiple-island chain, deducing the history of diversification on each island with their new approach for 14 different groups, or clades, of birds, insects, spiders, and plants.
The volcanic Hawaiian islands we see today emerged from the waves over a period of about 6 million years, carried northwestward as the ocean crust moved over from the hot spot that brought the magma from inside Earth to the sea floor to build the islands. Kauai emerged slightly more than 6 million years ago, the newest, the Big Island of Hawaii, only about 1.3 million years ago.
Each new islands, colonized by plants and animals of older islands, lead a wealth of new species that filled each island’s ecological niches. For instance, honeycreepers, an endemic group of bird species, and the unique silverswords filled all of Kauai’s carrying capacity -the number of species a particular ecosystem can support – within about 3 million years.
Marshall realized that “the progression of islands of the Hawaiian archipelago can be viewed as an evolutionary time machine,” revealing “rates of species-richness change for endemic species of the archipelago,” which has virtually no fossil record.
“It is increasingly appreciated that the biota of any particular place is a dynamic, ever-changing association of species,” Lim said. “The beauty of islands like Hawaii is that their geologic setting provides multiple temporal snapshots, and in so doing provides us a window to understanding the processes that have shaped its assembly through time.”