Do food availability, parasitism, and stress have synergistic effects on red colobus populations living in forest fragments?

Abstract

Identifying factors that influence animal density is a fundamental goal in ecology that has taken on new importance with the need to develop informed management plans. This is particularly the case for primates as the tropical forest that supports many species is being rapidly converted. We use a system of forest fragments adjacent to Kibale National Park, Uganda, to examine if food availability and parasite infections have synergistic affects on red colobus (Piliocolobus tephrosceles) abundance. Given that the size of primate populations can often respond slowly to environmental changes, we also examined how these factors influenced cortisol levels. To meet these objectives, we monitored gastrointestinal parasites, evaluated fecal cortisol levels, and determined changes in food availability by conducting complete tree inventories in eight fragments in 2000 and 2003. Red colobus populations declined by an average of 21% among the fragments; however, population change ranged from a 25% increase to a 57% decline. The cumulative basal area of food trees declined by an average of 29.5%; however, forest change was highly variable (a 2% gain to a 71% decline). We found that nematode prevalence averaged 58% among fragments (range 29-83%). The change in colobus population size was correlated both with food availability and a number of indices of parasite infections. A path analysis suggests that change in food availability has a strong direct effect on population size, but it also has an indirect effect via parasite infections.

Forest Fragmentation as Cause of Bacterial Transmission among Nonhuman Primates, Humans, and Livestock, Uganda

“…Chapman et al (15) recently showed that red colobus in forest fragments near Kibale suffer increased gastrointestinal parasitism with helminths as a result of nutritional stress and that this effect has led to a decline in population. Gillespie and Chapman (12) documented that the degree of disturbance of a fragment (measured as the density of tree stumps) was an accurate predictor of prevalence of infection of red colobus with parasitic nematodes.…”

“…Fragmentation also alters patterns of gastrointestinal helminthic and protozoan infection in certain species (12)(13)(14). Whether host susceptibility, transmission dynamics, or a combination of these factors drive such trends remains unclear (15). The effects of fragmentation on the dynamics of pathogen transmission between primates and other species, including humans, are largely unexplored.…”

The relationship between physiological stress and wildlife disease: consequences for health and conservation

“…This approach has been applied in a small number of stress and disease studies conducted on endangered species in challenging field conditions (Aguirre et al 1995;Chapman et al 2006). For example, plasma corticosterone positively correlated with fibropapilloma virus, an emerging disease threatening endangered green turtle (Chelonia mydas; Aguirre et al 1995).…”

Competing pressures on populations: long-term dynamics of food availability, food quality, disease, stress and animal abundance

“…To examine the possible role of stress in determining red colobus population numbers, Chapman et al quantified patterns of faecal glucocorticoid excretion in relation to food availability [74,75]. Poor nutrition and parasite infection were expected to lead to elevated glucocorticoid levels, and a time lag was expected before this became apparent.…”

“…Methods for sample processing and analyses can be found elsewhere [74,75,80]. Glucocorticoid levels from the two groups in Kibale were contrasted to levels from red colobus inhabiting eight nearby forest fragments [74].…”