Food for thought - one reason that big fierce carnivores are rare

In a paper published by Science today, 22 March 2002, Chris Carbone from the Zoological Society of London (ZSL) and John Gittleman of The University of Virginia, have formulated a unique way of predicting animal abundance - by comparing different animal species and the availability of their food. Their calculations not only show a common natural rule throughout a wide range of carnivore species but also could be a key tool for identifying declining carnivore species that require conservation measures.

Scientists have long been interested in understanding the causes of variations in animal abundance - which includes both their number and combined weight. Carnivores provide a unique group to study this issue and Carbone and Gittleman focused on species that feed on live prey and calculated animal density in relation to the total weight of prey available to these carnivores.

"By focusing on carnivores we found a common rule," explains Chris Carbone of ZSL. "Despite the great diversity among carnivores in size, social structure and prey , their abundance consistently changes in relation to their body weight and the amount of prey needed to support them. For example, we find that 10,000kg of prey can support 90kg of predator regardless of the species. So it could be either 90 individual 1kg mongooses or one 90kg jaguar."

Animal abundance is important for understanding the structure of animal communities, measuring biodiversity on the planet and is critical for conservation. It also allows the appropriate management of both wild and domestic animal populations.

Commonly, it is found that animal population density is associated with body size, where small species are found at higher density than large species and this is thought to be related to energetic needs related to size - big animals require more resources and so are found at lower density.

At the same time it is known from studies on single species, that population density is related to the abundance of food resources. Therefore more food rich habitats support bigger populations. While it is known that size and food availability affect population sizes, it has been very difficult to find data where both size and food richness can be compared across a range of species.

These predictions will help scientists to calculate the population of large carnivores which, in turn, can give vital base line information that can be used for the conservation of endangered species and can even be used to find suitable areas for re-introduction. It also allows for estimation of dwindling populations of carnivores that are hard to study because of their behaviour or remote habitats.

However, there are other factors that can influence the abundance of species, which often have conservation relevance.
"Species that violate our 'common rule' such as African wild dogs and lynx are likely to be feeding off a prey biomass that is declining or they are threatened by other factors such as poaching or predation," comments John Gittleman of the University of Virginia. "This is critical for understanding the conservation of carnivores as well as other endangered mammals."

Notes to Editors

• The Zoological Society of London is a registered charity dedicated to the worldwide conservation of animals and their habitats.

• A copy of this research article can be obtained by e-mailing scipak@aaas.org, +202-326-6440, alternatively see the Science Press Package page within EurekAlert!, http://www.eurekalert.org

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