Winter Weight Gain and Why There Are More Plants and Animals in the Tropics

January 22, 2014

Walrus. Photo: Captain Budd Christman, NOAA Corps

Every winter, no matter how hard I try to avoid it, I pack on five pounds. Perhaps it’s the big holiday meals or less time outside, but what if it’s just from being colder?

We know cold slows down the metabolism of many animals; it’s why bears, bats and groundhogs can go through the winter without eating.

The scientific evidence that ambient temperature affects metabolism comes not just from hibernating animals. Weirdly, it also comes from the study of biogeography.

One of the biggest questions in conservation science is why there are so many more plants and animals in the tropics than in the temperate regions such as North America and Europe.

A single acre of forest in the Amazon, for example, can have more species of trees than all of North America, and there can be more species of fish in an acre of coral reef in Indonesia than in all of the North Atlantic.

The fossil record suggests that greater tropic diversity of species has been true of a long, long time.

The Journal of Biogeography recently published an issue commemorating its 40th anniversary. Inside the issue is an outstanding article by Jim Brown presenting arguments and counterarguments for why there is more diversity in the tropics.

Brown makes a compelling case for temperature-driven diversity, summarizing his argument with a scene from Lewis Carol’s Through the Looking-Glass where “the Red Queen runs faster when she is hot.”

“The Red Queen runs faster when she is hot.” Credit: From Old Books,
“The Red Queen runs faster when she is hot.” Credit: From Old Books,

In other words, the warm and more consistent temperature of the tropics “affects the rate of metabolism and all biological activity.”

Plants and animals grow faster in the heat, and biological processes speed up, creating more diversity, which in turn begets yet more diversity. The end result is biological weirdness such as 30+ species of lemur on an island in the tropics or 347 species of reef fish in a single site.

It is not coincidence that the fattest animals in nature like walruses and bowhead whales live in cold climates, and biological diversity is lower where it’s colder. Temperature, metabolism and diversity are linked.

If you suffer from winter weight gain and someone notices, do what I do and blame it on the link between temperature and metabolism, and then quickly switch their attention by noting that this temperature-metabolism link is in fact the very reason why the variety of life in the tropics is so rich…

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