Effect of ecological factors on fine-scale patterns of social structure in African lions.

Abstract

Environmental variations can influence the extent to which individuals interact with other individuals by changing the value of grouping. It is well known that many species can form and disband groups, often in response to the distribution and abundance of resources. While previous studies showed that resources influence the broad-scale structure of animal groups, knowledge gaps remain on whether they affect fine-scale patterns of association among individuals within groups. We quantify association patterns in African lions while simultaneously monitoring the abundance and distribution of prey. We test how social and ecological factors, including individual trait (age, sex, reproductive state) similarity and prey availability (prey abundance, dispersion, herd size and body size) affect within-pride social structure in African lions. We found that individual decisions about associates depended on resource availability with individuals associating equally across all members of the pride when prey herds were scarce, aggregated or large bodied, and associating more exclusively (in subgroups of preferred associates) when prey herds were abundant, dispersed or small bodied. Individuals within lion prides seemed to be buffering against changes in prey availability by modulating their strength and density of connections with conspecifics when prides split into subgroups. The strength and density of connections among individuals within subgroups was greater when prey herds were large and lower when prey herds were dispersed or are large bodied. Our findings suggest that individual lions are making social decisions at both the subgroup level and the pride level, with decisions representing putatively fitness-enhancing strategies. Individuals were typically shifting between having few strong connections and having many weaker connections depending on prevailing ecological conditions, with prey abundance, dispersion and body size having the greatest impact on decisions about splitting into subgroups. The maintenance of connections within prides and subgroups in the face of ecological change suggests that the fission-fusion nature of lion prides might be essential for the long-term maintenance of social connections even when short-term conditions do not allow them. More broadly, our study reveals how fission-fusion dynamics and ecological factors can simultaneously have an effect on animals across multiple levels of sociality.