Socioecological theory, which attributes variation in social organization in female-bonded species to differences in within- and between-group feeding competition shaped by food distribution, remains largely unexplored in non-primate species. In the first such attempt on a non-primate mammal, we studied the patterns of agonistic contests within- and between-clans (the most inclusive social unit) of female Asian elephants with respect to food distribution, food abundance, and competitor density effects of group size and clan density. We directly quantified the distribution of grass biomass in different stretches of a grassland habitat around the Kabini backwaters, as well as the adjacent forest habitat, in Nagarahole National Park, southern India. We also quantified agonistic interactions among adult females in the grassland habitat to obtain rates of individual-level within-clan and between-clan agonism, and clan-level between-clan encounters. The occurrence of more frequent between-clan encounters in contrast to what was known from forest habitats, and stronger individual-level between-clan agonism than within-clan agonism was consistent with the grassland being a food-rich habitat patch as compared to the adjacent forest, as expected from socioecological theory. Within-clan agonism was not influenced by grass abundance or distribution within the grassland habitat, in contradiction to classic socioecological predictions, but interestingly increased with female group size until a group size of five, suggesting that the opposing forces of within-group and between-group competition may govern group size, as large group size is advantageous in this strong between-clan contest regime. The rate of (clan-level) between-clan agonistic encounters was positively explained by the number of clans. Although the rate of between-clan encounters was not related to grass biomass in focal zones, the duration of such encounters was positively related to grass biomass at the site of contest. We discuss contest competition in female elephant societies in the context of socioecological theory.
