Ecology of the Zanzibar red colobus monkey: Demographic variability and habitat stability

We examined the Zanzibar red colobus' (Procolobus kirkii) social structure and population dynamics in relation to the density, diversity and dispersio n of food resources in ground-water forest and agricultural land, which we characterized in terms of red colobus food species density, diversity, basa l area and dispersion. We used transect sampling and group follows to descr ibe population dynamics and social systems. Two agricultural areas, SJF Sha mba and Pete Village, had higher densities and more uniformly dispersed red colobus food tree species than those of the ground-water forest. Red colob us at these two sites had greater population densities and natality, and sm aller home ranges than red colobus in the ground-water forest, However, the se findings apply to a very small area of agricultural land (approximately 18 ha) that is contiguous with an area of the forest reserve having a high density of red colobus. It is not representative of agricultural areas else where on Zanzibar which support much lower densities or no red colobus. Alt hough agricultural areas contiguous with the forest reserve had high densit ies of red colobus, they appear to be very unstable. Within the agricultura l areas, we observed higher intergroup variation in group size and composit ion, study groups that decreased dramatically in size and disappeared from the study site, significantly lower levels of juvenile recruitment, and red colobus food trees that Exhibited definite signs of overbrowsing. This app arent instability in the subpopulation of red colobus utilizing agricultura l systems probably reflects the lower basal area of food trees and the grea ter fragmentation of suitable habitat and floristic dynamics duc to human a ctivities iii these areas. A fusion-fission social system occurred only in the ground-water forest subpopulation, which we hypothesize to be due to hi ghly clamped food resources.