Densités, biomasses et structures des populations d’Ongulés sauvages au Parc de l'Akagera (Rwanda)

Abstract

Population ecology of wild ungulates has been studied during two consecutive years (September 1968 -August 1970) in the Akagera National Park, Rwanda. Counts have been made four times a month on six line-transects using a technique similar to that of Lamprey (1963-64). Each of the 13 more common species has it own ecological preferences, and no inter-specific competition occurs (Table I). Average densities and standing crop biomasses are given for each of the major habitats of the area (Tables II, III, IV). The densities of sedentary species are remarkably stable from year to year. Average standing crop biomasses (fresh weight) range from 2705 Kg/Km2 in the Mutara grasslands to 28.286 Kg/Km2 in the tree savanas of the plains. Seasonal fluctuations are due to the seasonal breeding of some species and seasonal migrations of others. Data are given on the sex-ratio and age-ratio of the major species. Their social structure is described. Habitat is shown to influence social structure in the Topi and the Impala. Both species have different patterns of population dispersion and social grouping in different vegetation types. Among impalas, and apparently also among topis, the percentage of young of the year and juvenile individuals is smaller in areas of high population density.