Seasonal variation in the strength and consistency of tritrophic interactions among treehoppers, plants, and ants may favor generalist relationships

Abstract

Organisms interact with numerous species in their environment, and these interactions can influence a variety of social and ecological processes. Thus, temporal and spatial variation in species interactions is important for understanding the fitness consequences of multi-trophic relationships. Here, we investigate how tritrophic interactions between a host plant generalist sap-feeding insect, host plant species, and ant mutualists vary in a prairie habitat. We used field transects to quantify the abundances of three host plant species, three species of ants, and the treehopper Entylia carinata. We repeated the transects from Spring until late Fall to quantify seasonal changes in abundances, and across three years to investigate stability of tritrophic relationships across years. In the first year of the study, we also measured plant height. Finally, we characterized variation in the tending behavior of the three species of ants. We found that certain plant-ant species combinations are more common than others. While tritrophic associations between plants, ants, and treehoppers changed seasonally, they were largely stable across years. Furthermore, we found pervasive effects of ants on E. carinata, including E. carinata presence and abundance, E. carinata aggregation size and abundance, E. carinata nest presence and abundance, and E. carinata nest-tending behavior. Plant species had fewer effects, but affected E. carinata presence and abundance as well as the likelihood of E. carinata aggregations occurring on a plant. Finally, significant seasonal changes in ant abundances and ant tending rates create dynamic temporal variation in tritrophic interactions. The patterns observed are likely to have significant effects on E. carinata populations, and—due to the importance of ant-treehopper mutualisms in local ecosystems—cascading effects on local communities.