Luzon: The Island of Many Rodents

© Velizar Simeonovski, The Field Museum
© Velizar Simeonovski, The Field Museum / © Velizar Simeonovski, The Field Museum

In its purest form, science is about curiosity. It’s about asking new and weird questions, like “Why do apples fall out of trees?” or “Could this mold be useful?” or, in the case of researchers on the Philippine island of Luzon, “How many different kinds of rats do you think we can find?” The answer (to the last question, anyway) is “a lot.” In a paper published in Frontiers of Biogeography, researchers report the discovery of 28 previously unknown rodent species, most of which are completely unique to the island. 

The largest and most populous island in the Philippines, Luzon is better known among biologists as a hotspot of biodiversity. This is true of many islands, since their forced isolation from outside influences can create a sort of natural evolutionary laboratory, but Luzon takes it one step further. Far from the ground and from one another, the island’s many mountaintops create what scientists call “sky islands”—isolated, high-elevation habitats with their own adapt-or-die conditions.

The first recorded non-bat mammals on Luzon were described by naturalist Alfred Russel Wallace in 1880. He found only three species—a deer and two rats—and consequently judged the island to be poor in species variation. Just 20 years later, scientists already knew better, and the number climbed to 16. By the year 2000, researchers had recorded 28 different species, a majority of which belonged to the cloud rat (genus Phloemys) and earthworm mouse (genus Chrotomys) families. And, contrary to Mr. Wallace’s complaint, most of those species were also completely unique to the island.

It was this fact that piqued researchers’ interest. They decided to conduct a long-term survey of the island’s wildlife. Over the course of 12 years, they set traps at 17 different sites around the island. Some of the traps were nestled in the trees and vines while others lay on the ground. Knowing (or at least suspecting) their targets, the team baited some of the traps with juicy earthworms and others with lumps of fried coconut smeared with peanut butter.

The traps worked exactly as they were meant to: The researchers found plenty of animals from those unique-to-Luzon species. But they also found others. Many, many others. Nearly thirty, in fact.

A newly discovered tree mouse. Image Credit: © Larry Heaney, The Field Museum

Project leader Lawrence Heaney is the Negaunee Curator of Mammals at The Field Museum in Chicago. “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,” he said in a press statement. “We did not expect that we would double the number already known.”

And like their previously known brethren, the new species were a living furry testament to the island’s astounding variety of life.

“There are individual mountains on Luzon that have five species of mammals that live nowhere else,” said co-author Eric Rickart of the Natural History Museum of Utah. “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.” 

“Learning about the tremendous diversity of mammal species present on Luzon is crucial to conservation efforts,” Heaney added. “In order to be effective at conserving an environment, we have to know what’s out there.”

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