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Bad to be big: Why top predators struggle for survival

By Catriona Davies, for CNN
  • Large predators are more vulnerable to environmental change than smaller ones
  • Carnivores are affected as much by threats to their prey as by direct threats
  • Conservation needs to be more holistic, say researchers

London (CNN) -- Researchers have found new evidence on how tough survival can be for big predators such as tigers, lions, polar bears and leopards.

They discovered that large predators are much more vulnerable to environmental changes than smaller carnivores.

Philip Stephens, a biologist from Durham University in the UK, carried out the analysis of 200 previous studies. He said that the largest predators suffered a five to six fold greater decrease in relative abundance in response to a decrease in their prey.

The research was carried out with the Zoological Society of London and published in the Royal Society journal "Biology Letters". Stephens hoped it would help focus conservation efforts for large carnivores.

It illustrates how tough it is to be a big fierce predator.
--Philip Stephens, Durham University

"It illustrates how tough it is to be a big fierce predator," said Stephens.

"We already know they are slow to mature and reproduce, so are vulnerable to poaching; they need a lot of land, so are very vulnerable to habitat loss; but what is less well-known is that they are also critically dependent on the availability of their prey.

"It's one more insidious threat they are exposed to."

The results can give an insight into ways to help conservation of large animals, Stephens added.

He said: "It highlights the crucial importance of taking a holistic approach to conservation. We can't just focus our efforts on a given species because they are so dependent on each other.

"If we just focus on protecting big predators from direct killing or habitat loss, some of the other threats go unnoticed.

"Poaching the prey could be as much a problem for large animals as poaching the animals themselves."

The wild tiger population has dropped from 100,000 a century ago to just 3,600 today, according to World Wildlife Fund estimates.

Last month, leaders of 13 nations met for the first Tiger Summit in Russia to agree a Global Tiger Recovery Program aimed at doubling the number of the animals in the wild by 2022.

Stephens said: "We have just seen a lot of big gestures in the Tiger Summit. This study shows the importance of going beyond these big gestures. We need better protection of the entire habitat even if it comes at an economic cost, such as stopping logging in important areas.

"The last few decades we have seen a lot of public goodwill towards tigers, but these animals have still declined rapidly in number."

Stephens studied 11 carnivores: Least weasel, Arctic fox, Canadian lynx, European badger, coyote, wolf, leopard, spotted hyena, lion, tiger and polar bear.

His co-researcher, Chris Carbone, senior research fellow at the Zoological Society of London, said in a press release: "This study helps us to understand why large carnivores are particularly sensitive to environmental disturbance and why the protection and conservation of their habitat and, in particular, of their prey, are so important to global initiatives to save large carnivores in the wild."

The researchers said they have not yet fully explained the reasons for their findings, but believe that it is to do with the "high energetic costs of being big."

Their size might become a hindrance when times are tough, prey are rare, and individuals have to work harder to find their next meal, they said.