Latitudinal variation in behaviors linked to risk tolerance is driven by nest-site competition and spatial distribution in the ant Temnothorax rugatulus

Geographic range has long been noted to be associated with many organismic and ecological traits such as body size and species richness. However, much less is known about whether and how ecological variation across latitudinal gradients reflects behavioral variation. Ant colonies may also show behavioral variation, and Temnothorax rugatulus show a colony-level behavioral syndrome that seems to reflect risk tolerance across their North American range. While it is presumed that this pattern is the result of adaptation to local environmental conditions, which ecological factors are driving this variation are unknown. Here, we test if colony risk tolerance is affected by competition, predation, resource availability, or environmental stress at each site. Our results show that increased competition, specifically for nest sites, as well as increased spatial clustering of colonies predicts higher risk tolerance. Additionally, the spatial clustering of colonies influences the structure of the risk-taking syndrome, i.e., which colony-level behaviors are correlated and how strongly. This emphasizes the need for understanding large-scale geographic variation in behavior, as it may explain how ecological factors drive the evolution and maintenance of intraspecific behavioral variation across populations.