Rats! Changing rodent size linked to climate change



Rodent eating corn

Credit: Wikimedia

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You probably hadn't noticed, but the head shape and overall size of rodents has been changing over the past century - and now these changes have been linked to human population density and climate change.

For such size and shape changes to occur in a mammal all across the world, and in less than a century, is quite a substantial occurrence, said US ecologist Oliver Pergams, whose odd finding is reported in the current issue of online science journal PLoS One.

Pergams had done earlier studies on a century's worth of anatomic changes between two geographically isolated US rodents - Channel Island deer mice from coastal California, and white-footed mice northwest of Chicago - and noted fast changes among both.

"I suspected they weren't unique examples," he said. "I wondered whether these changes were occurring elsewhere, whether they were global in nature, and what some of the causes may be."

Pergams examined specimen rodents from museums around the world, recording more than 17,000 body and skull measurements from 1,300 specimens from 22 locations in Africa, the Americas and Asia.

The animals were collected from 1892 to 2001, and Pergams compared those from before 1950 to those collected after.

He also compared specimens gathered from sparsely populated islands to those from the mainland, where human populations were denser.

Pergams found both increases and decreases in the 15 anatomic traits he measured, with changes as great as 50 percent over 80 years. Ten of the 15 traits were associated with changes in human population density, current temperature, or trends in temperature and precipitation, he found.

"Rapid change, contrary to previous opinion, really seems to be happening quite frequently in a number of locations around the world," Pergams said. "There seem to be significant correlations with 'people-caused' parameters, such as population density and anthropologically-caused climate change."

While Pergams' study was by no means comprehensive, it was the first attempt of its kind to examine data on mammals from many global locations to find links between morphological change and variables such as population density and changing climate.

"Species can adapt quickly to rapid environmental changes - quicker than many people have thought, especially for mammals," said Pergams.

"Those mammals that can adapt quickly have a much higher chance to survive big environmental changes caused by humans. Understanding which species and populations have the greatest ability to change has a crucial impact on being able to conserve biodiversity."