In a study published May 20, a team of UC Berkeley researchers found that ectotherms — organisms that draw bodily heat from their environment — have difficulty adjusting to temperatures of either extreme cold or heat and therefore face more problems from global warming.
The study, a review of 112 published studies on thermal tolerance and plasticity in different animal species, examines ectotherms ranging from fish and insects to crustaceans and lizards. According to the researchers, a majority of these studies exposed animals to either low or high temperatures for a week or more. The animals’ mobility was then measured, and most were rendered immobile at extremely high or low temperatures, meaning that ectotherms have generally very low levels of thermal plasticity.
Campus postdoctoral fellow Alex Gunderson and campus assistant adjunct professor of integrative biology Jonathon Stillman composed the findings, which disprove a prevailing hypothesis: that geographical latitudes play a determining role in ectotherms’ heat tolerance.
According to the hypothesis, thermal fluctuation is greater at higher latitudes than at lower latitudes. The hypothesis states that thermal plasticity would seemingly be greater at higher latitudes to allow high-latitude organisms to cope with the temperature changes, because these organisms would experience more climate fluctuations.
“Previous studies investigating this question showed mixed support for this hypothesis,” said campus associate professor of integrative biology Caroline Williams in an email. “But without a global analysis that took into account many different kinds of animals, we couldn’t tell if maybe we were just using the wrong species.”
Williams said that the study is a “big step forward,” as it includes data from multiple independent studies on diverse aquatic and terrestrial taxa, which is a group of one or more populations of organisms. The study also revealed that among different groups of ectothermic species, thermal plasticity varies by habitat.
“Things that live in water — fishes and crustaceans — have more plasticity than things that live on land, and this was surprising,” Gunderson said. “We had no a priori reason to expect animals that live in water have greater plasticity than animals that live on land, but that is something we saw.”
According to Stillman, as temperatures rise across the globe, animals adapt to their changing environments. When environments experience extreme temperatures, however, they become uninhabitable. Because animals have low heat plasticity, they cannot remain in their own habitat and adjust their physiology, Stillman said — animals instead move to select climatic conditions in which they want to live.
“We are already seeing across the globe that as temperatures rise, animals are moving towards the poles,” Gunderson said. “Animals are moving to higher elevations. We are seeing wholesale shifts in communities in animals in where they live and what species are living together.”
The study allows scientists to better model species distribution, according to Stillman. By integrating heat-tolerance data into distribution models, scientists can more accurately map where a species is likely to relocate.
Stillman said that in using this information, the team can make conservation decisions that will preserve habitats which species use today as well as in the future.