May 14, 2009
Researchers studied the distribution and population of nine small mammals from live-trapping data over 30 years and notes from research museums covering the past hundred years. They utilized over 14,000 records covering the nine species.
"We're talking about the commonest mammals there, mammals that have considerable ecological impact," said lead author Philip Myers, professor of ecology and evolutionary biology at University of Michigan. "They disperse seeds, they eat seeds, they eat the insects that kill trees, they disperse the fungus that grows in tree roots that is necessary for trees to grow, and they're the prey base for a huge number of carnivorous birds, mammals and snakes. But we don't know enough about their natural history to know whether replacing a northern species with a southern equivalent is going to pass unnoticed or is going to be catastrophic. It could work either way.”
Southern red-backed voles are in decline due to climate change. Photo by: D. Gordon E. Robertson.
After compiling and studying 14,000 records, the researchers looked for an explanation.
"There's a lot more forest now than in the late 1800s and early 1900s, when logging and fires almost completely destroyed the forests of the northern Great Lakes region," Myers said. "But that doesn't work as an explanation for the patterns we see, because the species that are moving in and becoming more common are actually ones that do very well when forests are cut over."
In addition, changes in mammal distribution showed the same pattern in Michigan’s Lower Peninsula, where humans have increased over the past 50 years, as in the Upper Peninsula where the population has actually declined.
The scientists next set their eyes on climate change, researchers compiling minimum and maximum daily temperatures in the Upper Peninsula from 16 different weather stations. They found that temperatures increased significantly from 1970 to 2007 with average minimum temperatures increasing more than average maximum temperatures, leading the researches to believe that climate change is the primary cause for the changes in mammal distribution.
Other studies in North American have shown similar northward movements of mammals, including research in Ontario and Wisconsin.
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