Global warming probably won’t cause the total extinction of life, but scientists are worried that it will affect the loss of biodiversity-- certain species in certain areas.

Often we try and gather clues from extinction events to get hints about our future, but perhaps we’ve been missing the forest for the trees. Now, a team of researchers from Stanford and UC Berkeley are looking at past biodiversity loss for clues.

"If we only focus on extinction, we are not getting the whole story," said Jessica Blois, PhD, lead author of a study published online in Nature yesterday.

Focusing on the last major warming event about 12,000 years ago, Blois and her Stanford colleague Elizabeth Hadly searched the Samwell Cave near Mt. Shasta for small mammal fossils. They also sampled the modern small mammal community by doing some live trapping in the area of the cave. (Jenny McGuire, a graduate student at the UC Berkeley, did the radiocarbon dating of the samples.)

They found big changes in the small mammal population. "In the Pleistocene, there were about as many gophers as there were voles as there were deer mice," Hadly said. "But as you move into the warming event, there is a really rapid reduction in how evenly these animals are distributed.” As some species such as deer mice flourished, many other species declined.

Deer mice are considered a "weedy" species and, like the plants, don't have a strong habitat preference—they are generalists that will move in wherever there is an opening. When they replace other small-mammal species, the effects ripple through the ecosystem.

"Small mammals are so common, we often take them for granted," Blois said. "But they play important roles within ecosystems, in soil aeration and seed dispersal, for example, and as prey for larger animals." And different small mammals play those roles differently. What’s more, "Even though all of the species survived, small mammal communities as a whole lost a substantial amount of diversity, which may make them less resilient to future change," Blois said.

And according to Hadly, an extraordinarily rapid change is looming.

"The temperature change over the next hundred years is expected to be greater than the temperature that most of the mammals that are on the landscape have yet witnessed as a species," she said.

Creative Commons image by r.i.c.h.

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