A male drill (Mandrillus leucophaeus). Credit: Ola Olsson

Hunting for meat in the African rainforests has halved the number of primates. However, the hunting also has other negative consequences. The decline in the number of primates causes a reduction in the dispersal of seed by the primates, and this leads to a reduction in the numbers of important fruit trees and changes to the rainforest. This has been shown in new research from Lund University in Sweden.

The destruction of the world's rainforests is generally recognised as a major problem. However, it is not only felling and clear-cutting that change the rainforest. A research project at Lund University has looked at the effects of hunting on the forest. The researchers studied rainforests in Nigeria, where the local population hunts for food. The animals that are hunted include almost all mammals, including gorillas and chimpanzees and some small species of monkey.

"Hunting has a dramatic effect on the composition and structure of the forest, just as logging does, but without felling any trees", said Ola Olsson, a researcher at the Department of Biology, Lund University.

Both apes and small monkeys play an important role in seed dispersal in the rainforest, as they feed on a variety of different fruits. As the number of primates declines as a result of hunting, their seed spreading role also declines. If fewer fruit seeds are spread, fewer fruit trees will grow in the forests. Instead, species with wind-dispersed seeds will most likely take over.

Ola Olsson stressed that the present study does not give any definite answers to how the composition of the forests could change, but in his view, there could well be an increase in bushes and lianas. This would also have negative consequences for the local population.

"Many of the trees which have seeds that are dispersed by primates are also important to people, because those who live in the vicinity of the forests gather a lot of fruit and nuts", he said.

Moreover, a vicious circle arises, because primates cannot live in a forest without fruit trees. Ola Olsson would like to see better protection for nature reserves and national parks, and better information and education of local people in the villages. He remarked that the reasons for the hunting are somewhat complex. The meat forms a cheap and accessible source of protein for poor people, as well as a source of income if the carcasses can be sold in the towns, where people are prepared to pay high prices for ape meat.

"All our study sites are in protected areas, but the protection is insufficient", said Ola Olsson.

The trees also have other ecosystem functions, in the form of carbon sequestration and effects on nutrient cycling and retention. The researchers fear that when the composition of the tree species changes, there will be a knock-on effect on these processes. The study, which Ola Olsson has carried out together with Nigerian researcher Edu Effiom, has been published in the scientific journal Proceedings of the Royal Society B.

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