Should meat-eaters guide conservation?
Researchers disagree over whether predators reflect biodiversity.
Ecologists are divided over whether the predators inhabiting an ecosystem are a good guide to its total biodiversity. The debate may lead conservationists to reassess how they prioritize their efforts and design nature reserves.
Conservationists have long sought groups of species whose diversity reflects the total biodiversity in an area. Such indicators can help identify the places most in need of protection.
Based on their analyses of birds of prey, Fabrizio Sergio, at the Doñana Biological Research Station in Spain, and his colleagues have argued that top predators could be just such indicators1,2. Working in the Italian Alps, they have found that the number of birds of prey in a place is a good reflection of other species living there.
This seems to make sense. Top predators such as raptors and big cats need both large areas of habitat and healthy prey populations. And as predators have long been poster children for conservation, it would be handy if protecting them benefitted the habitat as a whole.
But, writing in the Journal of Applied Ecology3, a team of ecologists — led by Mar Cabeza at the University of Helsinki — argues that it's a mistake to generalize from studies of birds of prey, and that in general top predators give an uneven picture of biodiversity.
"To suggest that top predators make good biodiversity indicators when the research was conducted on raptors alone in a small region is dangerous," says Cabeza. "We must conduct further studies before making any recommendations."
Some predators, says Cabeza's team, will eat from several layers of the food chain, turning to insects if rodents aren't available, for example. This allows them to survive in quite degraded ecosystems. Madagascar, on the other had, has few predators, but many rare species found nowhere else.
Dave Augeri a conservation biologist at the Denver Zoological Foundation, agrees with Cabeza. "We can't say raptors indicate biodiversity, because even among this small group you have everything from specialized snail kites to red-tailed hawks which eat just about anything," he says. "We must work on a case-by-case basis."
Some conservation planning does focus on predators. The Yellowstone to Yukon Conservation Initiative to create reserves in the Rocky Mountains aims to protect areas where grizzly bears, wolves and lynx are found.
But not everyone takes this approach. "In South Africa, where I've done most of my work, conservationists would never designate protected regions based upon the carnivores," says Bob Smith, a conservation biologist at the University of Kent. "They would choose an area based upon plant and insect species and then add the carnivores later. You just can't work the other way around."
Sergio agrees that caution is needed when extrapolating results, but argues that no group has yet shown itself to be a better indicator than predators. "We must not dismiss the usefulness of predators just yet," he says.
At this stage, he wants to understand the relationship between predators and biodiversity more than its conservation implications. "They are looking at the application and we are looking at the biology," he says. "You cannot put the cart before the horse."
- Sergio, F., Newton, I. & Marchesi, L. Nature 436, 192 (2005).
- Sergio, F., Newton, I. , Marchesi, L. & Pedrini, P. J. Appl. Ecol. 43, 1049-1055 (2006).
- Cabeza, M., Arponen, A. & van Teeffelen, A. J. Appl. Ecol. doi: 10.1111/j.1365-2664.2007.01364.x (2007).