Tri-trophic interactions involving ants (Formica neogagates) taking caterpillar prey on hickory leaves (top left) as well as indirect effects of mutualistic interactions between sap-feeding membracids and ants (Camponotus chromaiodes) (top right). Rob Clark conducting field work for this project (lower left) and outreach education to the public (lower right). (All photos from Rob Clark.)
Several experiments conducted in the forest ecology project have focused on the role of ants in tri-trophic interactions. Rob Clark (Ph.D. ’16), and I received NSF support for his dissertation work evaluating the mechanisms by which ants exert strong or weak tri-trophic effects in this forest food web. Part of this research focuses on the keystone mutualism hypothesis, which states that food-for-protection mutualisms between ants and sap-feeding insects exert large indirect effects in ecological communities, much like keystone predators causing trophic cascades in marine ecosystems. Rob studied how ant-treehopper mutualisms alter the strength of top-down effects on coexisting caterpillars and cascade down to affect the growth of hickory trees, which commonly harbor ant-tended treehoppers and caterpillars. This work also tests whether the top-down effects of the ant-treehopper mutualism act through increases in the predatory behavior of individual ants, increases in population density of ants in the vicinity of treehoppers, or changes in ant community structure toward more predaceous ant species in the presence of treehoppers. Rob’s has published some of this work (Clark et al. 2016, Clark and Singer 2018) and is in the process of publishing more. He is currently a postdoc in the laboratory of Dr. Dave Crowder (Dept. Entomology, Washington State U.).