July 14, 2016
Where is the world's greatest concentration of unique species of mammals? A team of American and Filipino authors have concluded that it is Luzon Island, in the Philippines. Their 15-year project, summarized in a paper published in the scientific journal Frontiers of Biogeography, has shown that out of 56 species of non-flying mammal species that are now known to live on the island, 52 live nowhere else in the world. Of those 56 species, 28 were discovered during the course of the project. Nineteen of the species have been formally described in scientific journals, and nine are currently "in the works."
"We started our study on Luzon in 2000 because we knew at the time that most of the native mammal species on the island were unique to the island, and we wanted to understand why that is the case. We did not expect that we would double the number already known," said Lawrence Heaney, the project's leader, who is the Negaunee Curator of Mammals at The Field Museum in Chicago.
Luzon is the largest island in the Philippines; at about 40,000 square miles, it's a bit larger than Indiana. According to the authors, Luzon has never been connected to any continental land—the species have been isolated, like the animals that live in Hawaii. But Luzon is much larger and at least five times older than the oldest island in Hawaii, and so has had time for the few species that arrived from the Asian mainland to evolve and diversify greatly.
On islands, scientists sometimes see a "sped-up" version of evolution—when animals are closed off from the rest of the world, in places where there are few or no predators or competitors, they are able to branch out into special adaptations, eventually forming new species. And not only is the island of Luzon isolated, but it's covered in mountains. The mountaintops form what scientists call "sky islands"—little pockets of distinctive habitat that the animals further adapt to. "The animals are isolated high on the scattered mountains, so they inevitably diverge. Given enough time, you begin to see huge biodiversity," explained Heaney. "In the process of trying to understand how that happens, we doubled the number of known species on Luzon."
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