Habitat quality,population dynamics,and group composition in Colobus Monkeys (Colobus guereza)

Data from an Ethiopian population of Colobus guerezashow that territory size is fixed by the high density of the population. Groups undergo fission when their size results in fewer than 10 trees per individual within the group’s territory. The daughter groups produced by fission emigrate into suboptimal habitat, which acts as a demographic sink. Comparative analyses using data from other East African populations demonstrate that mean territory size is inversely related to population density and that density, in turn, is a function of the size of the forest block. Since both group size and reproductive rates can be shown to be positively correlated with type of forest, it is concluded that this relationship reflects the fact that local population densities reach their ceiling more rapidly in small forest blocks because the animals’ access to alternative territories is limited. The number of males in a colobus group is shown to be a function of the number of females in it. Multimale groups have lower reproductive rates than one-male groups, probably because the stress generated by competition among the males causes temporary infertility among the females.