BioEd Online

Large-brained animals may be less likely to go extinct in a changing world, perhaps because they can use their greater intelligence to adapt their behavior to new conditions, according to a new analysis.

Brain size relative to body size is relatively predictable across all mammals, says Eric Abelson of Stanford University. “As body size grows, brain size grows too, but at slower rate.” This creates a tidy curve. But some species have bigger or smaller brains than one would expect, given their size, putting them above or below the curve. And a bigger brain for body size usually means a smarter animal.

Abelson compared the size of these deviations from the normal curve with species fate in two groups. His “paleo” analysis looked at 229 species in the order Carnivora from the last 42 million years, about half of which are already extinct. His “modern” analysis looks at 147 North American mammals across 6 orders. Both studies produced similar results: species under 10 kilograms with big brains for their body size were less likely to go extinct or be placed on the International Union for Conservation of Nature (IUCN) red list for endangered species. Abelson presented his work on 16 July at the Society for Conservation Biology North America Congress for Conservation Biology in Oakland, California.

For larger species, the advantage of brains seems to be swamped by the massive disadvantage of being big. Large species tend to wait longer to reproduce, have fewer offspring, require more resources and large territories and catch the attention of humans, either as food or as a scary predator. A reduction in the area available to them or hunting pressure can hit them particularly hard.

But for the smaller mammals, the future may belong to the clever. Animals with bigger brains have been shown to be more likely to thrive when introduced to new places , and this new work suggests they would also outperform their dimmer peers when it comes to adapting to changes at home. The behavioral flexibility of the brainy may tide them over until the slower process of genetic change is able to catch up to a changed environment. “If it gets colder, I am not going to be able to evolve a harrier exterior,” says Abelson. “But if I can think to build a denser nest, then that cognitive flexibility can buffer me.”

The analysis joins many other investigations into the links between particular traits and extinction risk. Variations in body size, diet, population density, home range, life span, growth rate and many others having been tied to the risk of a species dying out. Walter Jetz, an ecologist at Yale, says that analyses using many traits will likely be more powerful and accurate than single trait predictions. Such analyses should also take climate change into account, says Jetz.

What to do with the interesting relationship between extinction risk and brain size is a question Abelson prefers to leave to others. One could argue for spending more energy on the smaller-brained, more vulnerable species that are at higher risk. Alternatively, you could decide that these dimwits are doomed and instead spend your energy smoothing the way for the smarter, more adaptable species, since they might be counted on to hold on if given a fighting chance. “All I can say is that I hope it is useful for whoever is making those decisions,” Abelson says.

Jetz agrees that the prescription for action doesn’t obviously follow from the result, but that hard decisions must be made. “Given limited resources and accelerated extinctions, triage may sometimes be the word of the day. But to do this responsibly, we first we need rigorous science to clearly, quantitatively and objectively identify the choices at hand.”