Difference in group size and age structure of African elephant in the nutrient-rich Serengeti and nutrient-poor Mikumi savannas in Tanzania

Abstract

Forage availability influences social behaviour and resource competition in group-living animals. African elephants (Loxodonta africana), as a group-living species, face significant resource competition. Thus, the elephants are likely to form larger groups and exhibit higher reproductive efficiency in dystrophic savannas, where forage quantity is greater than in eutrophic savannas. Female African elephants are highly social, forming family groups composed of genetically related adult females and their offspring of both sexes; whereas males at puberty disperse from their natal family to lead mostly solitary lives, at times forming a loose-knit bachelor group. The objectives of this study were to (i) determine the group size of African elephants in Serengeti National Park, a eutrophic savanna, and Mikumi National Park, a dystrophic savanna, and (ii) analyse the age structure of the elephant population in these parks during the dry season of 2014. Through direct observations, group type, group size and age composition were recorded following vehicular survey along road-transect. Group size, group type, and age composition of elephants were determined through direct observations. Family groups were significantly larger and had a higher proportion of pre-reproductive age classes in nutrient-rich Serengeti compared to nutrient-poor Mikumi National Park, contradicting our predictions. The size of bachelor groups did not vary between the parks, but Serengeti had a larger number of male elephants. The findings disclose the relationship between resource abundance and quality and elephant social dynamics. The study suggests appropriate measures for the conservation of African elephants in savanna ecosystems.