Joint Effects of Competitors and Herbivores on Growth and Reproduction in Aristolochia reticulata

Abstract

The separate and joint effects of herbivory and interspecific competition on an herbaceous plant were measured to determine to what extent, if any, herbivory and competition interact in their effects, and to test models of their joint effects. Plants of Texas Dutchman's pipevine, Aristolochia reticulata, were grown in a greenhouse, alone and in competition with either or both little bluestem grass, Schizachyrium scoparium, and southern dewberry, Rubus trivialis. Herbivory on A. reticulata by the pipevine swallowtail butterfly, Battus philenor, and on S. scoparium by cattle was simulated by clipping. Competition and clipping individually had the expected negative effects on A. reticulata growth and reproduction. The joint effect of competition and clipping on A. reticulata was best described as additive. The joint effect of the two competing species on A. reticulata in three—species mixtures was well predicted by a simple, but nonlinear, model that assumed that all three species competed for the same limiting resource. The results of this study suggest that the structure and dynamics of this community, and by extension those of other communities, can be understood by examining subsets of the community separately.