Do animals get bigger as the climate they live in gets colder? According to a rule established in 1847, they do 鈥� which has had biologists concerned over what climate change might do to animal body size. But now an analysis of the weights and geographical locations of nearly 274,000 individuals from 952 bird and mammal species has challenged the idea.
Bergmann鈥檚 rule, formulated in 1847 by German anatomist Carl Bergmann, states that an animal鈥檚 body size is negatively related to the temperature of its environment: smaller individuals of a species are found in hotter regions of the species鈥� range, while larger members reside in colder climes. Moose, for example, are supposed to get larger further north in their range.
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The rule, which most often refers to populations within a species but , has been invoked to explain observed body size patterns in moose, fish, reptile, bird and even human populations living at different latitudes. As the theory goes, having more body volume per skin area helps heavier members of a species stay warm when temperatures drop, including the Inuit, Aleut, and Sami people living near the poles.
No pattern
Now , an ecologist at the University of Florida, says there is no general rule. She collaborated with museum curators to compile raw data on hundreds of species. Only 14 per cent of the species showed support for Bergmann鈥檚 rule, while 7 per cent followed an opposite pattern. The majority of species showed no pattern at all.
鈥淧ast studies that confirmed Bergmann鈥檚 rule were mostly looking at just a few species at a time, over only small areas, or were data-limited,鈥� says Riemer. 鈥淲e only recently have access to these huge museum data sets and the tools to work with them.鈥�
, an ecologist at Tel Aviv University in Israel , says he is not surprised by Riemer鈥檚 findings, but worries they may have been affected by noisy data, and the聽decision to measure mass instead of body length. Another concern is 鈥渢he file drawer problem鈥�, referring to the greater likelihood of positive results to be published. This means literature surveys such as Meiri鈥檚 may not account for contrasting evidence present within a raw data set like Riemer鈥檚.
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