Scientists discover that climate change is threatening cold-blooded animals in a new way

All animals need energy to survive. They use it to breathe, circulate blood, digest food and move. Young animals use energy to grow, and later in life, to reproduce.

Body temperature increases the rate at which an animal uses energy. Because cold-blooded animals depend on the thermal conditions of their environment to regulate their body temperature, they are expected to need more energy as the planet warms.

However, our new research, published today in Nature’s Climate Change, suggests that temperature is not the only environmental factor affecting the future energy needs of cold-blooded animals. How they interact with other species will also play a role.

Our findings suggest that cold-blooded animals will need even more energy in a warmer world than previously thought. This could increase their risk of extinction.

What we already know

The amount of energy animals use in a given period of time is called their metabolic rate.

Metabolic rate is affected by various factors, including body size and activity levels. Larger animals have higher metabolic rates than smaller animals, and active animals have higher metabolic rates than inactive animals.

Metabolic rate also depends on body temperature. This is because temperature affects the rate at which the biochemical reactions involved in energy metabolism proceed. In general, if an animal’s body temperature rises, its metabolic rate will speed up exponentially.

Most animals alive today are cold-blooded, or “ectotherms”. Insects, worms, fish, crustaceans, amphibians and reptiles – basically all creatures except mammals and birds – are eutherms.

As human-caused climate change increases global temperatures, the body temperature of cold-blooded animals is expected to rise as well.

Researchers say that the metabolic rate of some ectotherms on earth may have increased by between 3.5% and 12% due to climate warming that has already occurred. But this prediction does not account for the animals’ ability to physiologically “adapt” to warmer temperatures.

Acclimation refers to the ability of an animal to remodel its physiology to cope with a change in its environment.

But acclimation can rarely completely negate the effect of temperature on metabolic processes. For this reason, by the end of the century it is estimated that the metabolic rates of land-based ectotherms will be about 20% to 30% higher than now.

If you have a higher metabolic rate, animals will need more food. This means they may starve if there is no more food available, leaving them with less energy to find a mate and reproduce.

Our research

Previous research efforts to understand the energetic costs of climate warming for ectotherms have been limited in one important way. They mainly used animals that were studied in relatively simple laboratory environments and the only challenge they faced was a change in temperature.

However, animals face many other challenges in nature. This includes interaction with other species, such as competition for food and predator-prey relationships.

Although species interact all the time in nature, we rarely study how this affects metabolic rates.

We wanted to examine how species interactions might alter predictions of the energetic costs of climate warming for cold-blooded animals. To do this, we turned to the fruit fly (from the genus Drosophila).

Fruit fly species lay their eggs in decaying plant material. The larvae that hatch from these eggs interact and compete for food.

Our study involved fruit kite species rearing alone or together at different temperatures. We found that when two species of fruit fly larvae compete for food at warmer temperatures, they were more active as adults than adults that did not compete with other species as larvae. This means they also used more energy.

From this, we used modeling to determine that species interactions at warmer global temperatures increase the energy requirements of fruit flies in the future by between 3% and 16%.

These results suggest that previous studies have not considered the energetic cost of climate warming for ectotherms. This means that physiological approaches alone are unlikely to be sufficient to understand the consequences of climate change for cold-blooded animals.

Let’s get real

Understanding the energy requirements of animals is important to understanding how they survive, reproduce and thrive in challenging environments.

In a warmer world, warmer ectotherms will need more energy to survive and reproduce. If there is not enough food to meet the energy demands of their bodies, their risk of extinction may increase.

Of course, we need to predict more precisely how climate warming will threaten biodiversity. This means studying animal responses to temperature change under more realistic conditions.

This article from The Conversation is republished under a Creative Commons license. Read the original article.