Struggle on the savanna: Leopards, wild dogs contribute to thorny landscape

October 16, 2014

GAINESVILLE, Fla. — In a classic food chain, predators, such as the sleek and strong leopard, eat herbivores — for instance, the slender and deer-like impala. In turn, herbivores eat plants.

But according to a new study co-authored by University of Florida associate professor of biology Todd Palmer and his recent postdoctoral student Jacob Goheen, that predator-prey relationship may be much more complicated, with broad implications for the habitats in which these animals live, such as the African savanna.

One benefit might be for the people who live in these areas.

“Because it’s a human-occupied landscape, we are interested in learning more about how people interact with this food chain,” said Palmer. “We’d like to know if the forage that impala don’t eat in dangerous areas can be used to save people’s livestock, especially in drought years. It would be very interesting to understand these types of linkages among carnivores, their prey and people.”

The study, published in the Oct. 17 issue of Science, was led by doctoral student Adam T. Ford at the University of British Columbia. The fieldwork was done at the Mpala Research Centre in Laikipia, Kenya, 100 kilometers north of the equator in a savanna — which is a mixture of trees and grasses — neither grassland nor forest. The team looked at three components of the ecosystem: the predators, including leopards and wild dogs; the leaf-eating impala; and two species of acacia trees, one defended by more thorns than the other.

“The work is essentially about the importance of predators in Africa in shaping the ecosystems in which they live,” Palmer said. “In a nutshell, predators create a landscape of fear, where their prey are too frightened to go into places where predators like to hang out. And where the prey do and do not go, it turns out, strongly influences the types of plants you find in these habitats.”

The team followed the movement of both predators and prey by using GPS telemetry. They observed that impala preferred to feed in less-risky, more open areas populated by herds of their kin, including other African ungulates such as dik-dik and elephants. In these less risky areas, the impala suppress the abundance of their favorite, less thorny, food plants. As a result, the acacia trees in these areas are better defended with an abundance of thorns, and thus, less appealing to the herbivores.

“If you walked into an area in the African bush and found it characterized by very thorny and well defended plants, you might never think that the ‘thorniness’ of the area was a result of where predators like to stalk prey,” Palmer said. “Yet, that’s exactly what we show.”

Basically, Palmer said, these herbivores “are caught between a rock and a hard place. They must avoid the claws and teeth of their predators and the thorns and chemicals of their food.”

Ultimately, the question the researchers want to answer is what kinds of widespread effects do humans have by driving the decline of top predators and their habitats?