Naked Tahitian Beauty
Posted by Richard Conniff on August 11, 2013
In the West, we’ve always thought of Tahiti as a hot spot, populated by bronzed beauties. And now it turns out to be true, though maybe not in the way you were thinking. Here’s the news, from ScienceDaily:
Picturesque Tahiti may be the hottest spot for evolution on the planet. A recent biological survey of tiny predatory beetles has found that over 100 closely related species evolved on the island in about 1.5 million years. Given Tahiti’s small area, slightly more than 1000 square kilometers, this adaptive radiation is the geographically densest species assemblage in the world.
The predatory beetles range in size from 3-8 mm long, and have evolutionarily lost their flight wings, making them homebodies living in small patches of mountain forest.
“It is exhilarating working with such a fauna, says James Liebherr of Cornell University, author of a new report in the journal Zookeys, “because every new locality or ecological situation has the high probability of supporting a species nobody has seen before.”
These beetles have diversified by speciating as fast as any animals worldwide, with each species estimated to last only 300,000 years before splitting into daughter species. Tahiti’s geological history has much to do with this evolutionary rate, as these beetles prefer to live in rain forests on high mountains. Their mountain territitories tend to become isolated through the same extensive erosion that has produced the broad, low-elevation river valleys so characteristic of the island. Yet some closely related species live on the same mountain ridge, just at different elevations or in different types of habitat.
This level of specialization is what characterizes an adaptive radiation, where species exist within narrow ecological or geographic boundaries that mainland species would simply ignore or fly over.
Yet this exuberant evolution may face a dark future, as invasive species from the mainland threaten the highly specialized island species. Predatory ants, such as the little fire ant, have invaded Tahiti, and have been recorded from some localities where native beetle species were collected by French entomologists in the 1970s.
“Now that the 101 species of small predatory beetles currently known from Tahiti can be identified, field sampling can be used to evaluate their conservation status relative to alien threats,” says Liebherr.
Finally, Liebherr offers one piece of travel advice that I have always endeavored to follow: Go, my son, but go pest-free. No, seriously:
”Everybody who makes landfall on Tahiti, either by air or sea, should endeavor to disembark pest free so as to protect the many denizens of the mountain forests who make the native ecosystems work.”
Source: James Liebherr. The Mecyclothorax beetles (Coleoptera, Carabidae, Moriomorphini) of Tahiti, Society Islands. ZooKeys, 2013; 322: 1