Document: TAT-3-42-25

Herbivore mediated apparent competition between two host plants in a New England salt marsh.

RAND, T.A.*

Brown University, Providence RI 02912 USA ¹

Abstract:
Herbivore damage to the salt marsh plant Atriplex patula, by the Chrysomelid beetle Erynephala maritima, is often more intense on plants that are associated with a second host plant species, Salicornia europaea, than on plants growing individually or with conspecifics. The objective of the study was to examine whether this pattern of associational susceptibility resulted in an herbivore mediated negative interaction, or apparent competition, between host plant species in the field. Host plant density /composition and herbivore presence or absence were manipulated in a factorial design. Host density manipulations included three treatments: Low density Atriplex plants, high density Atriplex monocultures, and high density Atriplex-Salicornia mixtures. In the presence of herbivores, Atriplex survival was lowest for plants growing with Salicornia, intermediate for plants in high density monocultures and highest in low density treatments. These differences in survival were not significant in herbivore exclusion treatments, indicating that the effects were indirectly mediated through herbivores rather than a direct competitive effect of plant neighbors. Egg and larval densities were found to be significantly greater in plots where Salicornia was present, resulting in greater plant damage in these same treatments. A strong tendency for females to oviposit in the vicinity of Salicornia, coupled with limited mobility of larvae at early instars, is likely to be responsible for driving the strong negative effects of Salicornia presence on Atriplex survival.

Keywords: Apparent competition, Associational susceptibility, Insect herbivory

This abstract is being presented at: 8:30 AM in session:
Oral Session #26: Invertebrate Herbivore - Plant Interactions.