|Tree-mouse, Credit: Larry Heaney|
Luzon is the largest island in the Philippines; at about 103,000 square kilometers, it's the 15th largest island in the world. The island has never been connected to any continental land which means that a lot of its biodiversity has 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, we sometimes see an acceleration of evolution. Animals are closed off from the rest of the world in places where there are few or no predators or competitors. This enables them 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. Mountaintops form "sky islands", little pockets of distinctive habitat that the animals further adapt to.
A team of American and Filipino authors have studied the mammalian fauna of Luzon Island over 15-years and summarized their findings in a new paper. They showed that out of 56 species of non-flying mammal species that are now known to live on the island, 52 are endemic. Of those 56 species, 28 were discovered during the course of the project.
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.
Among the 28 new species discovered by the team are four species of tiny tree-mice with whiskers so long they reach nearly to their ankles, and five species of mice that look like shrews and feed primarily on earthworms. Most of the new species live in tropical cloud forest high in the mountains, where frequent typhoons can drop four or five meters of rain per year.
All 28 of the species we discovered during the project are members of two branches on the tree of life that are confined to the Philippines. There are individual mountains on Luzon that have five species of mammals that live nowhere else. That's more unique species on one mountain than live in any country in continental Europe. The concentration of unique biodiversity in the Philippines is really staggering.
We reject the general assumption that mammals on tropical oceanic islands are sufficiently well known that analysis and modeling of the dynamics of species richness may be conducted with precision. In the development of conceptual biogeographic models and implementation of effective conservation strategies, existing estimates of species richness, levels of endemism, and the number of subcenters of endemism should be actively reassessed and verified through robust field, museum, and laboratory studies.