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Monkey-dung study offers clues about land-use, wildlife ecology

April 07, 2006

Fecal matter of red colobus monkeys collected in western Uganda has yielded a wealth of knowledge about human land-use change and wildlife health and conservation. The main lesson, researchers say, is that the intensity of tree removal translates directly to parasite populations and the risk of infection of their hosts.

In an effort to glean predictive power out of years of research on the effects of forest fragmentation on various species and ecological processes, researchers looked at nine differently fragmented regions of forests located in what is now agricultural landscape just west of Kibale National Park, in the foothills of the Ruwenzori Mountains. Within these regions, they focused on populations of red colobus (Piliocolobus tephrosceles) monkeys and the presence of strongyle and rhabditoid nematodes.

For two years, Thomas R. Gillespie, a professor of pathobiology in the University of Illinois College of Veterinary Medicine, and Colin A. Chapman, an anthropologist at McGill University in Canada, surveyed the monkeys and determined nematode levels by examining 536 colobus fecal samples. Their study appears in the April issue of the journal Conservation Biology.

Gillespie is co-director with Illinois pathobiology colleague Tony Goldberg of the Kibale EcoHealth Project, a flagship program of the multidisciplinary U. of I. Earth and Society Initiative on Emerging Disease & Ecosystem Health.

Red colobus are one of the most endangered African colobine species. The two groups of nematodes have been documented to infect red colobus and have the capacity to cause gastrointestinal problems that can be fatal.

Gillespie and Chapman sorted through nine potential factors, including physical and biological attributes. They concluded that the degradation of the forest and human presence, as measured in stump density, strongly influenced the prevalence of parasitic nematodes. Infection risk, they reported also was higher in the fragment with the highest stump density than in the fragment with the lowest stump density.

"Our results provide evidence that an easily measured index such as the number of stumps in a given area can be used to predict the degree to which a fundamental ecological process - host-parasite dynamics - can be altered by human disturbance," Gillespie said. "We think that this pattern is likely to be common in disturbed areas and may represent an unrecognized threat for the conservation and management of various habitats."

Gillespie, who also holds appointments in the anthropology department and the Program in Ecology and Evolutionary Biology at Illinois, and Chapman, also a researcher for the Wildlife Conservation Society, were part of a team that last year reported that selective-logging practices in the region had changed the ecological balance for three primate species. The red-tailed guenon, they noted in the Journal of Applied Ecology, is still a primate in decline. They also reported high levels of parasitic infections in the guenons in the heavily logged areas.

The parasites being monitored in their studies occur at high frequency in human populations in the logged region, but are absent from colobus species within Kibale National Park, where people and primates interact less frequently, Gillespie said.

Physical factors considered in the new study included size, location and landscape of each of the nine fragmented regions, while biological factors in the mix were tree diversity, tree density, stump density and overall colobine density. Colobines are leaf-eaters that live in groups of five to 300 individuals, and they depend on forest cover to survive.

University of Illinois at Urbana-Champaign