Elephants have difficulty keeping cool while traveling long distances
Claudio Blaslavski/500px/Getty Images
Researchers have found that for animals weighing more than one tonne, the main speed limiting factor is the difficulty of staying cool when traveling long distances, whether running, swimming or flying. increase.
The findings suggest that global warming will be an even bigger problem for large animals than previously thought. “If our model is correct, large animals should generally be less active or shift to more nocturnal behavior,” says Alexander Dyer of the German Center for Integrated Biodiversity Research in Leipzig. say.
Dyer and his colleagues began by creating a database of maximum persistence speeds for over 500 species of animals, from insects and fish to whales and elephants. They included only studies of wild, free-roaming animals, excluding studies of captive animals, for example based on video recordings, radar or tracking devices.
They found that locomotion speed increased as animals grew larger, and when their weight reached 1000 kilograms, speed plateaued and began to decrease. The team considered several possible explanations and concluded that a simple model that estimates how much an animal would need to slow down to avoid overheating could explain the shape of the curve.
The problem is that muscle is fundamentally very inefficient, says Dyer.
Small animals can lose this extra heat quickly due to their high surface area to volume ratio, but for larger animals this heat becomes a major problem.
This seems to be just as big of a problem for swimming animals, even though their bodies can release heat faster in water than in air. Dyer believes it’s because they have a lot of insulation to keep them warm. “Heat dissipation is a property of the animal, not the medium through which it travels,” he says.
“In my opinion [the team] Make a convincing argument that large-bodied animals face additional metabolic constraints on maximal velocity associated with overheating,” said Walter Jetts of Yale University.
“This is an important fundamental insight, but it also has conservation relevance. Larger species, which are often endangered by the population, may be particularly at risk.”
No living flying animal weighs much more than 15 kilograms. However, many flying pterosaurs were larger than this, so releasing excess heat was a bigger problem for them. “I guess they had a role in thermoregulation,” says Dyer.
Rising temperatures are especially challenging for large animals, but as the planet warms, staying cool is becoming a problem for many small animals as well. Some animals have evolved smaller bodies to help them react and lose heat faster.
Several members of the team have previously examined how size relates to the animal’s total speed over short distances. They concluded that maximum velocity in large animals is limited by the time it takes to accelerate, rather than by the ability of the muscles and bones to withstand the forces involved, as previously suggested.
During sprinting, muscles rely on stored energy rather than aerobic respiration as they do over long distances, and large animals run out of energy before reaching their maximum theoretical velocity.
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