Living on the edge: life-history of olive baboons at Gashaka-Gumti National Park, Nigeria.

Baboons are the most successful and ubiquitous African primates, renowned for their behavioral and reproductive flexibility, which enable them to inhabit a wide variety of habitat types. Owing to a number of long-term field studies, comparative behavioral, developmental, demographic, and life-history data are available from several populations, but study sites show a heavy bias toward South and East African savannahs, with little research in West or Central Africa. Life-history data from such areas are important if we are fully to understand the nature of the environmental factors that limit baboon distribution. Here, we present demographic data for olive baboons at Gashaka-Gumti National Park (GGNP), Nigeria, collected from December 2000-February 2006, and use these data to test comparative models of baboon life-history. The GGNP habitat, which includes large areas of rainforest, is an environment in which baboons are little studied, and rainfall is much higher than at previous study sites. GGNP troop size data are presented from censuses, as well as life-history data for two troops, one of which is within the park and wild-feeding (Kwano troop), whereas the other dwells at the park edge, and supplements its diet by crop-raiding (Gamgam troop). Troop sizes at GGNP are small compared with other field sites, but fit within previously suggested ranges for baboons under these climatic conditions. Inter-birth intervals in Kwano troop were long compared with most studied populations, and values were not as predicted by comparative models. Consistent with known effects of food enhancement, Gamgam troop experienced shorter inter-birth intervals and lower infant mortality than Kwano troop. We indicate some possible factors that exclude baboons from true rainforest, and suggest that the clearing of forests in Central and West Africa for agricultural land may allow baboons to extend their range into regions from which they are currently excluded.