An ecological perspective on human densities in the central African forests.
Factors determining human densities in the central African forests are examined and compared with the predictions from an agronomic model by the Food and Agriculture Organization, United Nations Fund for Population Activities and International Institute for Applied Systems Analysis. Published data on crop yields, wild and domestic herbivore densities and human densities are compared along the rainfall gradient and between three broad geological classes representing low, medium and high soil nutrient availability. Crop yields show no increase with rainfall; both manioc and maize may decrease at higher rainfall levels. There are large differences between geological classes in cattle density. Within each geological class human densities increase with rainfall. Geology and rainfall together explain three-quarters of the variance in human densities over much of sub-Saharan Africa (33 out of 40 countries). The predictions from the agronomic model are very different from the actual patterns revealed by the analyses of crop yields, wild and domestic herbivores and humans in relation to geology and soils. Game resources are the limiting factor for humans.