Rising temperatures may cause problems for cold-blooded critters

Last year in the pages of Science News, I tried to answer a question: Will the world’s plants, animals and other organisms be able to adapt to climate change? There wasn’t an easy answer to that question, in part because the effects of climate change are varied (they include rising air temperatures and acidifying oceans) and also because there are several ways for organisms to “adapt.”

Genetic traits might evolve in the animals that let them survive in the new conditions they encounter, for instance. Many other organisms will rely on flexibility in behaviors or other features, such as finding new sources of food or living in warmer waters without overheating. Figuring out the capacity of a species to adapt in any of these ways in pretty difficult, but scientists are trying.

Those scientists include Alex Gunderson and Jonathan Stillman of the University California, Berkeley and San Francisco State University. These biologists wanted to determine the potential for ectotherms — cold-blooded creatures — to tolerate the higher temperatures that climate change is bringing.

Earlier biologists had developed a couple of hypotheses about how ectotherms should respond. First, the wide swings in seasonal temperatures seen at higher latitudes should mean that species found in those locations will be better able to handle rising temperatures than ones found in the tropics. And second, since organisms from extreme environments tend to have lower flexibility, or plasticity, when it comes to temperature, tropical species should have the most trouble dealing with warming conditions.

To test those hypotheses, Gunderson and Stillman looked at 112 previously published studies and gathered data on 232 cold-blooded species, including insects, amphibians, lizards, fish and crustaceans. They considered each species’ upper and lower level of thermal tolerance, which they defined as the point where it couldn’t move fast enough to avoid getting eaten. Then they fed all their information into a computer to see what patterns emerged. Their study appears May 19 in the Proceedings of the Royal Society B.

Neither hypothesis panned out. And while that may seem like good news for tropical species, it’s actually bad news for ectotherms in general, because they tended to all have little capacity for tolerating the heat. “Our results indicate that physiological plasticity may do little to buffer ectotherms from rising temperatures,” the researchers write.

Aquatic organisms appear to have a bit more of a safety margin than land species, the analysis found. That may have something to do with the “Bogert effect,” which refers to the ability that many creatures have to adjust to environmental changes through behavior. That may reduce the selection pressure on the evolution of plastic traits.

Because land animals can often deal with higher temperatures by, for example, hiding out in the shade, there hasn’t been as much need for them to evolve the capacity to deal with really hot weather, Gunderson and Stillman note. Sea creatures may not have to deal with a similar range of temperatures, but many of them have less ability to react behaviorally, so they have had to evolve a bit more flexibility to just deal with it.

Given that the safety margins for all cold-blooded species was found to be pretty low, though, I wouldn’t hold out hope that the aquatic species will be much better off than the terrestrial ones.