Small mammals – and the rest of the food chain – at greater risk from global warming than previously thought, say Stanford researchers

Louis Bergeron in Stanford University News: The balance of biodiversity within North American small-mammal communities is so out of whack from the last episode of global warming about 12,000 years ago that the current climate change could push them past a tipping point, with repercussions up and down the food chain, say Stanford biologists. The evidence lies in fossils spanning the last 20,000 years that the researchers excavated from a cave in Northern California.

What they found is that although the small mammals in the area suffered no extinctions as a result of the warming that occurred at the end of the Pleistocene epoch, populations of most species nonetheless experienced a significant loss of numbers while one highly adaptable species – the deer mouse – thrived on the disruptions to the environment triggered by the changing climate.

"If we only focus on extinction, we are not getting the whole story," said Jessica Blois, lead author of a paper detailing the study to be published online by Nature on May 23. "There was a 30 percent decline in biodiversity due to other types of changes in the small-mammal community."

The double whammy of late Pleistocene warming, coupled with the coinciding arrival of humans on the North American continent, took a well-documented heavy toll on the large animals. Almost a third of the big, so-called "charismatic" animals – the ones with the most popular appeal for humans, such as mammoths and mastodons, dire wolves and short-faced bears – went extinct. But until now, little had been done to explore the effects of that climate shift on smaller fauna.

…[A]ccording 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. "The small-mammal community that we have is really resilient, but it is headed toward a perturbation that is bigger than anything it has seen in the last million years."

A deer mouse, the ultra-cute carrier of hantavirus. Shot by James Gathany, Wikimedia Commons via the Centers for Disease Control