Carnivore extinction risk determined more by biology than human population density

Carnivores around the world are more at risk of extinction due to their own intrinsic biological attributes than from an increasing human population with whom they share their space, say scientists in a study published this week. Researchers looking at all 280 carnivore species around the world estimated the risk of their extinction by 2030 based on a variety of different threats.

They found that while a high human population density is associated with a high extinction risk, its importance fell as biological traits were accounted for. Four traits in particular were associated with high extinction risk in carnivores: a small geographic distribution, low population density, high trophic level (position on the food chain), and long gestation period.

Furthermore, biology is by far more important in determining risk of extinction when combined with high human population density. “When species face severe external threats, their biology becomes much more crucial,” says Dr Marcel Cardillo, a postdoctoral research fellow in the Department of Biological Sciences at Imperial, and first author of the paper.

Writing in the July issue of PLoS Biology, the authors conclude that there is no room for complacency about the security of species simply because they are not currently considered globally threatened.

“There is a strong case to be made for pre-emptive conservation of species — that live in regions of rapid human population growth and have a biology predisposing them to decline,” they write. They highlight in particular the threat to African viverrids, or civets and genets, even though they are currently considered relatively safe.

The authors, from Imperial College London, University of Virginia, USA, and the Institute of Zoology, suggest action now would offset greater danger later: “Arguably, maintaining the stability of particularly susceptible species before they become threatened could be more cost-effective in the long term than postdecline attempts to rescue them from the brink of extinction,” they conclude.

They suggest pre-emptive action including the establishment of population monitoring programs, or listing species under national species protection laws on the basis of potential future susceptibility.

“We need to keep an eye on species before they start declining to extinction,” said Dr Cardillo. “What we think is safe now may soon go through a rapid decline. We shouldn’t be too confident about the species around us now.”

“This is a preliminary study, the first to examine a global level of extinction risk at the species level and at the same time consider biology’s intrinsic influence. Now we intend to extend our methods to all 4,500 terrestrial mammals, to see if there are general predictors of extinction risk and that these rules apply between orders of animals.”

In the PLoS study, the researchers took all 280 of the well-characterised carnivore species and assessed human impact on each of them using the human population density within their geographical distribution. This was tested together with a range of biological traits, to determine the most important predictors of extinction risk status, within a comparative statistical model.

As a measure of extinction risk status they took each species’ position on the IUCN-World Conservation Union Red List which rates how likely a species is to become extinct, ranked in six categories from ’Least Concern’ to ’Critically Endangered’.

The research was funded by the Natural Environment Research Council, Conservation International’s Center for Applied Biodiversity Science and the National Science Foundation.