Heterogeneity in resource competition covaries with individual variation in long-term social relationships

Competition for resources (such as food, water, and mates) is a main driver of group-living because the extent of competition can either positively or negatively affect social interactions. We show that the differences in resource competition and habitat that individual dolphins experience correlates with the number and type of relationships they have and that this differs between males and females. These findings highlight how different environmental conditions can drive variation in individual's long-term social relationships. Resource competition among conspecifics is central to social evolution, as it serves as one of the primary selective pressures of group living. This is because the degree of competition for resources impacts the costs and benefits of social interactions. Despite this, how heterogeneity in resource competition drives variation in the type and quantity of long-term social relationships individuals foster has been overlooked. By measuring male mating competition and female foraging competition in a highly social, long-lived mammal, we demonstrate that individual variation in long-term intrasexual social relationships covaries with preferred habitat and experienced resource competition, and this effect differs based on the sex of the individual. Specifically, greater resource competition resulted in fewer social preferences, but the magnitude of the effect varied by both habitat and sex, whereas for social avoidances, both the directionality and magnitude of the effect of resource competition varied by habitat and sex. Together our work shows how fine-scale variation in individual socioecological niches (i.e., unique physical and social environments) can drive extensive variation in individual social behavior (here long-term relationships) within a population, thereby broadening current theories of social evolution.

Automated summary

The competition for resources and differences in habitat affect the social interactions and relationships of individual dolphins, with variations seen between males and females. These findings highlight the influence of environmental conditions on long-term social relationships of individuals.