Cloud rats of sky island: the Philippine island with the highest number of unique mammals

On the ever-branching Tree of Life, the tropical island of Luzon has two branches all to itself – 93 per cent of its mammal species live nowhere else on Earth.

15th July 2016
A tree-dwelling mouse, a forest in Luzon (© Larry Heaney, The Field Museum) and cloud rats (© Velizar Simeonovski, The Field Museum)

A tree-dwelling mouse, a forest in Luzon (© Larry Heaney, The Field Museum) and cloud rats (© Velizar Simeonovski, The Field Museum)

Like many of us on holiday, evolution does peculiar things on an island. Big, old and isolated, Luzon Island in the Philippines is the perfect laboratory for natural selection to tinker with any species that happen to find their way onto its shores. And tinker it has.

After conducting a five-year study of Luzon’s native mammals, excluding bats (and humans), an American and Filipino team has found that 52 out of 56 species are endemic to the island, living nowhere else on Earth.

New frontier

The results of the study, published in the journal Frontiers of Biogeography, confirms Luzon as the place with the highest concentration of unique mammal species in the world. Some of these include “cloud rats” which look rather like tree-dwelling guinea pigs with squirrel tails, and mice with an array of whiskers that stretch from their snout to their feet.

The researchers actually discovered 28 of the 56 species while they were conducting the study. When they began the project in 2000, they already had an idea that many of Luzon’s mammals were endemic to the island, but not quite how many. “We did not expect that we would double the number already known,” says Lawrence Heaney, project leader and Negaunee Curator of Mammals at the Chicago Field Museum.

An island lifestyle

So where did all these new species come from? It’s the same question Darwin asked on the Galapagos, where his ideas of evolution first began to coalesce. And it’s not hard to see why – with fewer competitors and predators, and with ecological niches just waiting to be filled, islands are cauldrons of evolutionary change. Cut off from the pesky interference of outside gene pools, island species gradually become more and more distinct from their mainland cousins, until scientists can tell the difference between them and give them their own name.

These differences can also exist within the same island. Think of the mountain ranges covering Luzon as “sky islands”, geographical barriers that create ecosystems within ecosystems. “There are individual mountains on Luzon that have five species of mammals that live nowhere else,” explains Eric Rickhart of the Natural History Museum of Utah. “That’s more unique species on one mountain than live in a country in continental Europe.”

Unfortunately, it turns out that by the time these species were first studied, many of them were already endangered. Nearly 93 per cent of the Philippines’ old-growth rainforests have been lost due to deforestation, but the team hope that their discoveries will help lead to more effective wildlife conservation. After all, in order to best protect a species, we need to find them first.

May the search continue…

 


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