Biggest carnivores most vulnerable: study
The largest and most powerful carnivores may also be the most vulnerable to extinction, new research shows.
Ecologists at the Zoological Society of London believe the biggest flesh-eating carnivores are more at risk of dying out than smaller animals because of the amount of energy they expend to catch big prey.
The findings were published Tuesday in the journal PloS Biology.
"Following our analysis, large-prey feeders have higher energy budgets and need higher gain, which puts them at a more vulnerable place," lead researcher Chris Carbone told the CBC.
The scientists calculated the energyrequirements of land-dwelling carnivores and found that once an animal reaches a body mass ofone tonne, it has arrived at a threshold where "the sheer cost of capturing and running and pulling down your big prey" surpasses the energy rewards from the meal.
Carbone explained that carnivores can be grouped into two categories: smaller predators such as house cats and badgers, which feed on comparatively small mammals such as rodents or earthworms, and animals larger than 20 kg.
"It's above 15 kg or up to 20 kg that we see an abrupt shift," Carbone said. "Suddenly not only are they feeding on larger prey, but for example lions are actually feeding on prey such as wildebeests or zebras, which are equally big or more powerful than the lions themselves."
At least four carnivorous mammals near the one-tonne mark have died off, Carbone said: the short-faced bear, the sabretoothed cat, the North American lion, and a wolf-like carnivore from 25 million years ago called the Megistotherium osteothlastes.
The largest existing carnivore, the polar bear, can weigh from 500 kg toone tonne, meaning polar bears are susceptible to the intake equation. "At some point, the intake rate would not be sufficient to compensate for hunting even bigger prey," Carbone said.
Polar bears hibernate and nap to make up for energy costs, he said, but while the payoffs for each kill are still very large, throughout most of evolutionary time it has taken one-tonne animals too much energy to sustain themselves.