![]() One female with known age, born during the study in April 1995, had her first baby at an age of 11 years and 4 months. Western gorillas in the Mbeli Bai population were weaned (last time seen suckling) at an average age of 4 years and 9 months, which is 16 months later than in mountain gorillas. Recent analysis from the long-term data at Mbeli Bai indicates that indeed western gorillas are weaned at a later age compared with mountain gorillas and indicate a slower physical maturation for immatures. So far the long-term data required to investigate whether western gorillas have a different maturation pattern compared to mountain gorillas has been lacking. Gorillas are an interesting genus to investigate in order to ascertain whether the more frugivorous western gorillas mature more slowly because they occur in very different habitats: the seasonal lowland forest with many fruit trees at one extreme and the high-altitude montane rainforest with its dense herb availability at the other. ![]() Under this hypothesis more folivorous animals are expected to show rapid growth rates in the earlier stages of ontogeny and cease growth earlier than nonfolivorous/frugivorous species. This strategy helps to reduce the risks of starvation (due to intraspecific feeding competition) by spreading the metabolic needs for juvenile growth. In environments with poorer and unstable or unpredictable food availability, maturation is expected to take longer. Maturation rates and life-history parameters are seen as evolutionary adaptations to different ecological and social conditions. This is in strong contrast to chimpanzees or bonobos in which captive animals mature much faster than those in the wild, because food provisioning under captive conditions accelerates physical maturation. Our knowledge of the physical maturation of wild gorillas is mainly based on studies of mountain gorillas carried out at the Karisoke research station gorillas in that population show very similar life history milestones compared to captive western gorillas. In zoos it is common for female gorillas to give birth before reaching 10 years. Gorillas are known among the great apes for their fast life history patterns.
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