Social uncertainty influences the balance of quantity and quality of cooperative relationships

Raven Hartman , Gerald G Carter

Many group-living animals develop stable affiliative social relationships that benefit survival and reproduction but also require investments of time and energy (in activities like social grooming). These social investments serve two key functions: building new social relationships (“diversifying”) and maintaining existing ones (“focusing”). The ‘social bet-hedging’ hypothesis states that the optimal balance of diversifying and focusing depends on the stability or predictability of the social environment: all else being equal, focusing is favored more when partners are reliably available, whereas diversifying is favored when it is more difficult to predict which partners will be available to help in the future (i.e. “social uncertainty”). To assess this idea, we created an evolutionary agent-based model of how vampire bats form cooperative relationships with realistic patterns of foraging, social behavior, ageing, reproduction, and death. To manipulate social uncertainty in our simulations, we adjusted the rates of roost switching, foraging success, and predation. We then determined how social uncertainty impacted the relative success of six “social investment strategies” that determined how much the bats diversified allogrooming across partners. We show that, under a wide range of conditions, (1) selective allogrooming creates new reciprocal food-sharing relationships which increase survival, (2) an optimal degree of diversifying balances the benefits of relationship quantity and quality, and (3) social uncertainty consistently selects for more diversifying. Our model shows how species-specific social stability can determine the optimal social investment strategy for balancing relationship quantity versus quality.