The Hot Zone

Getting smaller

Posted by Alison Hawkes on August 30, 2010
Category : Climates of the Past

Global warming is causing many changes in species. Some are going extinct, others thriving, habitats are shifting, and ecosystems are reacting to changes in temperature, precipitation, acidity, and more.

But could a global increase in temperature also change the morphology of a species? If the past is any indication, then add size and shape to the list. A study undertaken by the Florida Museum of Natural History and available online in the Journal of Mammalian Evolution (to be published in print in December) posits that a largish hyena-esque animal shrank in size during a warming event 55 million years ago.

In 200,000 years, Palaeonictis wingi went from bear size to coyote size, a 50 percent drop, as temperatures spiked some 15 degrees Fahrenheit along with CO2 levels.

Palaeonictis skull at the Museum für Natürkunde, Berlin

This fits into a pattern of animals getting smaller in warmer weather. The same change has been observed in herbivorous mammals, as nutrient levels in plants tend to decline in higher CO2 conditions. Even today if you look at bears, the ones in Alaska are much bigger than the ones roaming Montana. Cold weather seems to spawn bigger beasts.

But why? Palaeonictis, which lived in Europe and North America was a mostly meat-eating omnivore that may have found a big meal harder and harder to get, as prey got smaller. The relationship between predator and prey sizes tend to track along the same line. Palaeonictis was one of the largest mammalian predators at the time in North America, making it “reasonable that [it] may have decreased in body size in response to the reduced average size of its mammal prey … ,” the authors write.

Increasing aridity, due to less rainfall and higher temperatures, might also have had an effect on our prey-dependent Palaeonictis. When the productivity of the ecosystem declines, it reverberates up through the food chain.

What could all this eventually mean for today’s carnivores? Lions the size of tomcats? Bears weighing in alongside a standard poodle?

-Alison Hawkes

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