Trait-mediated indirect interactions in invasions: unique behavioral responses of an invasive ant to plant nectar

Abstract

*[In this study, we tested the hypothesis that the highly invasive ant species, Anoplolepis gracilipes, exhibits stronger trait changes in response to increasing levels of nectar than co-occurring, less invasive ant species. Across 2 islands in the Samoan Archipelago, we located multiple sites dominated by A. gracilipes & multiple sites dominated by other, less invasive species. At each site, we manipulated nectar levels on a common extrafloral nectary-bearing shrub & assessed short-term changes in ant worker recruitment & aggression. We found that the recruitment response of the highly invasive ant species A. gracilipes was not unique: other dominant ant species also increased recruitment in response to increasing nectar levels. However, A. gracilipes did show unique changes in aggressive behaviors: as nectar levels increased, the proportion of prey discovered, attacked, & removed by A. gracilipes workers & the speed at which they performed these aggressive behaviors all increased strongly. Other ant species showed no such responses. In addition, fewer subordinate ants persisted on plants at sites invaded by A. gracilipes. Finally, plot-level, simultaneous manipulations of ant access to the plants & nectar availability demonstrated that Morinda citrifolia-ant mutualisms influenced the b-diversity of local arthropod communities differently when A. gracilipes dominated local ant assemblages.]