On Friday, NASA issued a news release stating that 2014 was the warmest year on record. Two groups of scientists at NASA and the National Oceanic and Atmospheric Administration (NOAA) independently arrived at this conclusion after analyzing surface temperature measurements from over 6,300 sites all over the world collected over the past year. Since 1880, the average surface temperature on Earth has risen by roughly 0.8°C or 1.4°F. As temperatures continue to climb, ecosystems and animals are forced to adapt or risk becoming endangered.

Cold-blooded animals, or ectotherms, rely on environmental heat sources to help their bodies reach an optimal temperature. Because their bodily functions are directly linked to and influenced by external temperatures, rises and fluctuations in temperature pose a serious challenge to ectotherms.

To better predict how resilient cold-blooded animals are to climate change, Australian researchers at the University of Sydney and the University of Queensland combed through over 4,000 papers looking for data on how ectotherms change their physiology in response to changes in external temperature. They used data from 205 studies published between 1968 and 2012 to generate the largest database on physiological adaptability in cold-blooded animals.

In each study, the physiological response to a change in external temperature was measured by changes in the metabolic rate, heart rate, movement, enzyme activity or a combination thereof. The researchers also looked at two different types of physiological responses: an acute response following an immediate and rapid change in the environmental temperature and a “post-acclimation” response after the animal was allowed to adjust, or acclimate, to the new temperature for a period of time.

When the results were broken down by habitat, the researchers found that marine and freshwater ectotherms responded less and were more resilient to changes in temperature when they had time to acclimate. On the other hand, terrestrial ectotherms’ responses to temperature changes were the same whether or not they had time to adjust. Marine and freshwater animals that lived in environments where the temperature was fairly constant were less sensitive to temperature changes than animals that lived in environments where there is a lot of flux. In contrast, terrestrial animals from warm environments were less sensitive to temperature changes than animals from cool environments.

Having a large dataset also allowed the researchers to look at whether or not physiological rates, such as heart and metabolic rate, have increased over the last 20 years. They found that for terrestrial and freshwater ectotherms, their metabolic rates from 1990-2010 were higher than the average rate from 1900-1990. The past 20 to 30 years also happens to be when the majority of the Earth’s warming happened. Marine ectotherms seem to be less affected by temperature flux because the magnitude of temperature change in the ocean is smaller than on land or in freshwater.

The picture emerging from this and similar studies is both hopeful and worrying. We can be hopeful because animals seem to possess a natural resilience that enables them to adapt to changing environments. But there is a limit to their adaptability. Animals can only change their bodies and physiologies so much before their internal systems become off-balanced and stop working. The adaptive responses of these animals simply cannot keep up with the pace of climate change, especially if temperatures continue to rise as they have for the past three decades.

References:
Seebacher, F., White, C., & Franklin, C. (2014). Physiological plasticity increases resilience of ectothermic animals to climate change Nature Climate Change, 5 (1), 61-66 DOI: 10.1038/nclimate2457