Birds Key to Serengeti Ecosystem

A leopard naps in a tree in Serengeti, Tanzania. Credit: Barbara Schneider, stock.xchng

Elephants have been among the species severely affected by poaching in the Serengeti National Park. Felix Borner-www.wildlens.com/AAAS-Science

Wildebeest grazing along the Serengeti Plain in Tanzania. Credit: John Fryxell/University of Guelph

Seed-eating birds in the Serengeti are necessary in order to maintain the forest, scientists said this week. An absence of the birds would result in a decline in trees.

In the journal Science, Gregory Sharam and colleagues describe exactly how birds help to maintain forests in the Serengeti ecosystem by keeping the local seed-killing beetles in check. They also demonstrate what can happen to the forests if the birds disappear.

Their study illustrates, first, how a stable community is maintained, and second, how it can unravel with a single disturbance, the journal's editors said in a statement.

The scientists used a 40-year data set from Tanzania to study the interconnected relationships between the birds, the bruchid beetles, and the trees. They observed that, for the most part, the beetles only fed upon fallen seeds that birds had not yet eaten – but not on seeds that birds had already ingested and processed. In that way, the birds protect the seeds (and forest) through their feeding, but in their absence, the beetles can cause major reductions in seed germination.

The birds fed mostly on seeds among dense trees and closed canopy, but not so much among sparse trees and open canopies. So, when disturbances such as fires open up the forest canopies, the birds do not return and the forests do not recover their original densities.