Scientists discover a new way climate change threatens cold-blooded animals

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

Elevated body temperature increases the rate at which an animal uses energy. Because cold-blooded animals rely 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 Climate Change, suggests that temperature is not the only environmental factor influencing 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 can 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 several 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 biochemical reactions involved in energy metabolism proceed. In general, if an animal’s body temperature increases, its metabolic rate will accelerate exponentially.

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

As human-induced climate change increases global temperatures, the body temperatures of cold-blooded animals are also expected to rise.

The researchers say that the metabolic rate of some land-based ectotherms may have already increased between 3.5% and 12% due to climate warming that has already occurred. But this prediction does not take into account the ability of animals to naturally “acclimate” to higher temperatures.

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

But rarely can acclimation completely reverse the effect of temperature on metabolic processes. For this reason, by the end of the century terrestrial exotherms are still predicted to have metabolic rates about 20% to 30% higher than they are now.

Having a higher metabolic rate means animals will need more food. This means they can starve if there is no more food, 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 exothermics have been limited in one important respect. They mostly used animals studied in relatively simple laboratory environments where 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 constantly in nature, we rarely study how this affects metabolic rates.

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

Fly species lay their eggs in rotting plant material. Larvae that hatch from these eggs interact and compete for food.

Our study involved rearing fly species alone or together at different temperatures. We found that when two species of fruit fly larvae competed for food at higher 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 infer that species interactions in warmer global temperatures increase the future energy needs of fruit flies by between 3% and 16%.

These findings suggest that previous studies have underestimated the energetic costs of climate warming for exothermics. This means that purely physiological approaches to understanding the consequences of climate change for cold-blooded animals are likely to be inadequate.

Let’s get real

Understanding the energy needs of animals is important for understanding how they will survive, reproduce and evolve in harsh environments.

In a warmer world, warmer exotherms will need more energy to survive and reproduce. If there is not enough food to meet their body’s energy requirements, their risk of extinction may increase.

Clearly, we need to more accurately predict how climate warming will threaten biodiversity. This means studying animal reactions to temperature change under more realistic conditions.

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