Habitual tool use on monopolizable resources affects group cohesion

Zoë Goldsborough , Margaret Crofoot, Julián León, Pedro Luis Castillo-Caballero, Evelyn del Rosario-Vargas, Brendan James Barrett 

Tool-aided extractive foraging changes animals’ interactions with their environment by expanding access to novel and/or high-quality foods. If and how habitual reliance on tool use impacts animals’ social dynamics is less understood. If materials for tool use are monopolizable, tool use might increase intragroup competition. While higher intragroup competition encourages greater group spread, this lower cohesion comes at the cost of increased vulnerability to predation and intergroup competition. We examined how use of spatially fixed, monopolizable resources (i.e., anvils) influences group cohesion by comparing groups of tool-using and non-tool-using white-faced capuchins (Cebus capucinus imitator) living on Jicarón island in Coiba National Park, Panama. Jicarón lacks terrestrial mammalian predators and habitual stone tool use at spatially fixed anvils is locally restricted to a ~1.5 km coastal stretch. We deployed two grids of 24-25 camera traps to compare daily activity patterns, as well as temporal variation in party size, party composition, and spatial cohesion between tool-using and non-tool-using capuchins.
We found that tool-using capuchins were more likely to exhibit smaller and less variable party sizes than non-tool-using capuchins, and that adult females and adult males were less likely to co-occur in a sequence. Tool-using and non-tool-using capuchins showed different spatiotemporal cohesion; consistent with a more cohesive non-tool-using group and fission-fusioning or less cohesive tool-using group. Although only male capuchins use tools, the entire tool-using group appears to show reduced cohesion, suggesting that increased competition experienced by one sex can have cascading effects on all group members. Our findings suggest that habitual tool use relying on spatially fixed, monopolizable resources incentivizes higher group spread, creating differences in the social environment of tool-using and non-tool-using animals sharing the same habitat.