Priority effects in the establishment of the oak leaf tie community

A variety of caterpillars build leaf tie shelters, which are subsequently colonized by other arthropods. Our past research has shown that leaf-tiers will push each other to gain access to a pre-existing tie. Some species are more aggressive than others, which suggests that the level of aggression displayed by the caterpillar may influence the abundance and composition of subsequent occupants. Patterns of community assembly such as this in which the identity of the initial colonist influences the composition of the final community are termed priority effects. The goal of this study was to discover how differences in aggression between species lead to priority effects in the composition of leaf tie communities.

We compared arthropod communities that colonized leaf ties initially containing a caterpillar to empty control ties. The initial colonists used, in decreasing order of aggression, were Psilocorsis cryptolechiella, P. quercicella, and Pseudotelphusa quercinigracella. Experimental leaf ties were made in the field by clipping together leaves of understory white oaks and placing a single caterpillar between the leaves. These leaf ties were surveyed one or two weeks after their creation to determine the identity of all occupants. This experiment was repeated multiple times throughout the summer. We found differences in the composition of arthropod communities residing in leaf ties that initially contained different species of caterpillars both one and two weeks after the leaf ties were built. This is the first study of priority effects in a large arthropod community and provides insight into how natural communities assemble.