Do plant herbivores and pathogens differentially affect native and exotic plant species in a wetland restoration experiment?
G. Kai Blaisdell, Bitty A. Roy, Laurel E. Pfeifer-Meister and Scott D. Bridgham, Center for Ecology and Evolutionary Biology, University of Oregon, 5289 University of Oregon, 335 Pacific Hall, Eugene, OR 97403
Restored wetlands often have lower plant diversity than relatively undisturbed reference sites, and hence native plants in restored wetlands may be vulnerable to enemy attack. In May 2006, we examined herbivore and pathogen damage on the three most common grass species in a wetland prairie restoration experiment in Eugene, Oregon. We found significantly more combined pathogen and herbivore damage on the invasive Lolium multiflorum than on either of the two native species Agrostis exarata or Deschampsia cespitosa. This indicates that the invasive species L. multiflorum may harbor more natural enemies than the two dominant native species. During June-August 2006 in the same experiment, we examined herbivore and pathogen damage to 10 native perennial grass and forb species across a gradient of diversity and relative abundance of native and exotic species (as measured by percent cover). For herbivore damage, we found a significant effect of species and a significant positive correlation with standing dead thatch. For pathogen damage, we found a significant effect of species and a significant positive correlation with the ratio of exotic:native plant cover. Pathogen damage on native plant species increased as relative abundance of exotic cover increased. Our results did not find support for the enemy release hypothesis, but we did find evidence of enemy spillover from exotic to native species.
