Study indicates species extinction is not a random event

By Fariss Samarrai

A new study indicates that thousands of bird and mammal species worldwide are at greater risk for extinction than previously thought because they possess certain identifiable risk factors. The findings were reported in the April 14 issue of the journal Science.

"Our findings suggest that extinction events result in a further loss of biodiversity, possibly even the extinction or threatening of thousands of additional species of animals, including large, charismatic ones such as rhinos and chimpanzees," said John L. Gittleman, associate professor of biology at U.Va., one of the study's authors.

"We have identified a number of characteristics that make certain species prone to greater extinction risks, and we have determined that extinctions do not occur randomly. Species that are biologically prone to certain risk factors are far more likely to go extinct than suggested by models of random extinction. The resulting potential loss of biodiversity is enormous."

Gittleman said the biological characteristics that place mammal species at greater risk of extinction include eating high on the food chain, low population density, long gestation length, and especially small geographic range size.

"We believe that the threat of extinction for many species is real and because of a cluster effect could result very quickly in further loss of biodiversity and genetic history," Gittleman said.

Species that have many close relatives are the most likely to be saved from extinction, Gittleman said, but species that are of a unique lineage with few relatives, such as the giant panda, are at severe risk. Once lost, there would be a significant loss of evolutionary history as well.

Gittleman pointed out that in addition to the particular biological characteristics that make some species prone to extinction, there are several environmental factors that also can accelerate risk.

"Many species become endangered because of human activity such as habitat destruction for agriculture or development purposes, and by exploitation of species through fishing and hunting. Many species also become threatened by the introduction of exotic species and disease. The reality is, extinctions are not random events."

The other authors of the study are Andy Purvis and Paul-Michael Agapow of the Department of Biology, Imperial College, U.K.; and Georgina M. Mace, Institute of Zoology, the Zoological Society of London.