Locations like Madagascar and the Galapagos Islands are traditionally seen as the poster boys of evolutionary theory, but they may have just been shoved off their pedestal by the island of Luzon in the Philippines. Researchers there have recently discovered 28 new unique species of mammal. This brings the total number of non-flying mammals on the island to 56, 52 of which (93 percent) are endemic to Luzon, meaning they are not found anywhere else on the planet.
Prior to beginning their work back in 2000, the researchers were aware of 23 unique non-flying mammals on Luzon, although during their 12 years in the field they discovered so many new species that they now believe the island boasts a higher concentration of endemic mammals than any other location.
In a statement, study co-author Eric Rickart explained that “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.” More specifically, all of the new species belong to two diverse endemic clades known as cloud rats and earthworm mice.
Among these new discoveries is a mouse with whiskers so long that they extend all the way down to its feet, as well as a bat that’s so small it can sleep in the hollow gaps inside bamboo stalks.
Writing in the journal Frontiers of Biogeography, the study authors explain that Luzon’s incredible array of endemic inhabitants is largely caused by the fact that it is an extremely old volcanic island, which rose from the sea around 27 million years ago, rather than breaking off from mainland Asia. As such, the creatures living on Luzon have evolved in isolation over an enormous timescale, resulting in a huge degree of speciation.
On top of this, the island contains a number of towering mountain peaks, referred to as “sky islands”. Mammals living on these mountaintops are therefore cut off from one another, and have consequently evolved to become endemic not only to Luzon, but to their specific patch of high-altitude terrain.
According to Rickart, “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.”
In total, the researchers have identified eight centers of local endemism on the island, and also report that the number of unique species on any given mountain is directly correlated with its maximum elevation, with high-altitude locations boasting four or five times as many endemic mammals as lowland sites.
From this, they conclude that sky islands play a significant role in enabling endemic species to evolve, and that altitude is therefore a “key component of the generation of patterns of endemism.”
Image: This tree-dwelling mouse has whiskers that reach down to its ankles. LARRY HEANEY, THE FIELD MUSEUM