GORILLA ECOLOGY AND BEHAVIOR

Many factors influence the evolution of primate grouping patterns, inc luding phylogeny, demographic and life-history variables, and ecologic al factors such as access to food, predation pressure, and avoidance o f infanticide. The interaction between these factors determines social organization.(1) Because western lowland and mountain gorillas differ so dramatically in their habitats and foraging strategies, they provi de a valuable opportunity to assess how changes in ecology influence t his balance. Mountain gorillas live in high-altitude montane forests, are herbivorous, and live in stable and cohesive groups. Western lowla nd gorillas live in lowland rainforest and are much more frugivorous t han mountain gorillas. It is not yet clear to what extent incorporatin g significant quantities of fruit in the diet influences western lowla nd gorilla sociality because they have been studied much less than hav e mountain gorillas. However, what is known about their behavior hints that there may also be considerable differences in their social organ ization, including changes in group size and cohesion and in the frequ ency and type of intergroup encounters. Gorillas thus provide a unique opportunity to reevaluate proposed models of ecological influences on social organization in African apes.