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Logging changed ecological
balance for monkeys, damaged health
Barlow, Life Sciences Editor
photo to enlarge
by Kwame Ross
researcher Thomas R. Gillespie, a postdoctoral fellow
in veterinary pathobiology, said intense selective
logging changed the ecological balance for three primate
CHAMPAIGN, Ill. —
Twenty-eight years after intense selective logging stopped in the region
now known as Uganda’s Kibale National Park, the red-tailed guenon
(Cercophithecus ascanius) is a primate still in decline.
The logging practice, scientists report in a new study, changed the
ecological balance for these monkeys, leading to behavioral changes
and opening the door for multiple parasitic infections.
photo to enlarge
colobus (Colobus guereza)
focused on three primate species, collecting 1,076 fecal samples from
the heavily logged area and from an undisturbed, nearby forest from
August 1997 to August 2002 as part of a longitudinal study of logging’s
impact. The samples came from red-tailed guenon, red colobus (Piliocolobus
tephrosceles) and black-and-white colobus (Colobus guereza) and were
analyzed for the eggs and larvae of worms and protozoan cysts.
The study appears online ahead of publication in the Journal of Applied
While the three primate species were subject to a higher risk of infections,
only the guenons (pronounced GWINN-ins) suffered from an increased number
of parasites, including three parasites not found in undisturbed forest.
In the selective-logging area, more than 50 percent of the trees, many
of them the food sources for the mostly fruit-eating guenons, had been
“We saw dramatic changes in the prevalence of infection and in
the frequency of multiple infections in these logged areas,” said
lead researcher Thomas R. Gillespie, a postdoctoral fellow in veterinary
pathobiology at the University of Illinois at Urbana-Champaign.
“When you see infection characteristics like these, they can be
associated with very detrimental effects on the host.”
Since the logging period of the late 1960s, red-tailed guenons have
been appearing in much lower densities, he said.
What once were large groups with multiple males and females are now
fragmented, with much smaller groups living isolated and spread out
more widely than in undisturbed forest, where often the three species
“When we look at their numbers over time, they continue to decline
28 years later,” Gillespie said. “The red colobus numbers
declined at first but are now recovering. The black-and-white colobus,
perhaps due to a release of competition, have increased in the logged
Because the two colubus species primarily eat leaves, it is believed
that they can adapt more easily to disruptions in their habitat, he
Gillespie initiated the research as an EPA fellow and doctoral student
at the University of Florida. He continues the work at Illinois to better
understand the interplay between habitat disturbance and primate conservations
and health in Uganda. He is collaborating with veterinary pathobiologist
Tony Goldberg and other researchers at Illinois, where state-of-the-art
facilities and faculty expertise are uniquely suited for studying disease
emergence, zoonotic diseases and the consequences of land-use changes.
In August, Gillespie will become the first director of the new Earth
& Society Initiative on Emerging Disease & Ecosystem Health
at Illinois. The initiative coordinates a diverse assemblage of the
university’s centers, programs, laboratories and individuals whose
current interests focus on the interface between emerging infectious
diseases, anthropogenic environmental change and conservation.
The researchers have monitored the three species, gathering data immediately
after logging, 12 years later and again 28 years after the logging ended.
“We know land-use change is affecting wildlife species,”
Gillespie said. “We know that there is a conservation issue. It’s
been difficult to understand what is taking place. No one had really
looked at how parasites and disease might be affecting this relationship.”
“We were surprised to find dramatic patterns across the board,
where the species of primates doing poorly in logged areas had a much
higher prevalence of parasitic infection and more types of parasites
affecting them simultaneously,” he said.
Gillespie and co-authors Colin A. Chapman of McGill University in Canada
and Ellis C. Greiner of the University of Florida found that red-tailed
guenons had a much higher prevalence of infection with seven gastrointestinal
parasites in the logged forest than in the undisturbed one. The parasites
found in the guenons were Trichuris sp. (whipworms), Oesopohagostomum
sp. (nodular worms), Entamoeba coli, Entamoeba histolytica, Iodamoeba
buetschlii, Strongyloides fulleborni and Streptopharagus sp.
Additionally, the red-tailed guenons in the logged forest were the only
primates of the three species infected with Chilomastix mesnilia, Giardia
lambila and a Dicrocoeliid liver fluke. These parasites did not appear
in guenons in the undisturbed forest.
The researchers also noted that the patterns of forest regeneration
in the aftermath of logging appear to be more favorable for colobus
monkeys than for the guenons. Citing their own as-yet unpublished data,
and that of Karen Rode of Washington State University, the researchers
suggest that reduced food availability has led to dietary stress. The
guenons in the logged forest, they report, are getting much less protein
and vital minerals than their counterparts in undisturbed forests.
Recovery of the forest also has been hampered by the growth of acanthus,
an invasive shrub that has overwhelmed much of the forest floor where
trees were removed, Gilllespie said. Because elephants love to eat the
shrub, they trample through the clearings, adding yet another obstacle
for the growth of new trees, he said.
“Knowledge of how particular species are affected by various forms
of ecological change is essential to promote land-use policy that is
compatible with animal and human health and biodiversity conservation,”
Gillespie, Chapman and Greiner wrote in the conclusion of their study.
The U.S. Environmental Protection Agency’s National Center for
Environmental Research, Ford Foundation and Wildlife Conservation Society
funded the research, which was done with permission of the National
Council for Science and Technology and the Uganda Wildlife Authority.