Interspecific competition influences the composition of ecological communities. Species may differ in their needs for different resources, therefore resource availability may determine the outcome of interspecific interactions. Species often compete over food, shelter or both. When more than one resource is limited, different species may prioritize different resources. To determine the impact of resource availability on the competitive relationship between an invasive and a native species, we examined interactions between groups of the invasive Argentine ant ( Linepithema humile ) and the native odorous ant ( Tapinoma sessile ) over (1) food, (2) shelter or (3) both simultaneously. We further examined the mechanisms underlying the competitive relationship, asking whether aggressive interactions, exploratory behaviour or the order of arrival at a resource explained resource use. Shelter was preferred by both species when no competitors were present. In a competitive setting, L. humile groups controlled shelter through aggressive displacement but lost control over food due to investment of workers in the control of shelter. Thus, there are tradeoffs when competing over multiple resources and aggressive interactions allow invasive species to displace native species from a preferred resource. This article is part of the theme issue ‘Intergroup conflict across taxa’.
Variation in individual behavior among group members impacts collective outcomes. The ability of both individuals and groups to outcompete others can determine access to resources. The invasive Argentine ant, Linepithema humile, dominates resources and displaces native species. To determine how access to resources by groups of L. humile is impacted by their behavioral composition, we first determined that L. humile workers consistently vary in aggressive behavior. We then asked if variation in aggression within a group influences the group's ability to access a resource in the presence of cues of a native species, Tapinoma sessile. We found that the behavioral composition of L. humile groups impacted the groups' collective response to cues of T. sessile. Group behavior was the result of mostly additive, rather than synergistic, combinations of the behaviors of the group members. The behavior of groups that contained 50% highly aggressive and 50% low-aggression individuals was similar to the average of the behaviors of groups of all highly aggressive and groups of all low-aggression individuals. Uncovering the mechanisms that allow social invasive species to dominate the ecological communities they invade can inform the mitigation of invasion.
Elucidating the mechanisms underlying differentiation between populations is essential to our understanding of ecological and evolutionary processes. While social network analysis has yielded numerous insights in behavioral ecology in recent years, it has rarely been applied to questions about population differentiation. Here, we use social network analysis to assess the potential role of social behavior in the recent divergence between two three-spined stickleback ecotypes, “whites” and “commons”. These ecotypes differ significantly in their social behavior and mating systems as adults, but it is unknown when or how differences in social behavior develop. We found that as juveniles, the white ecotype was bolder and more active than the common ecotype. Furthermore, while there was no evidence for assortative shoaling preferences, the two ecotypes differed in social network structure. Specifically, groups of the white ecotype had a lower clustering coefficient than groups of the common ecotype, suggesting that groups of the white ecotype were characterized by the formation of smaller subgroups, or “cliques”. Interestingly, ecotypic differences in the clustering coefficient were not apparent in mixed groups composed of whites and commons. The formation of cliques could contribute to population divergence by restricting the social environment that individuals experience, potentially influencing future mating opportunities and preferences. These findings highlight the insights that social network analysis can offer into our understanding of population divergence and reproductive isolation.
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