Document: EVA-3-99-147

Does lack of herbivory and disease explain the success of an alien plant species: Experimental tests.

SIEMANN, E.* and W.E.ROGERS

Rice University, Houston, TX 77251 USA ¹

Abstract:
Alien plants are usually introduced with few or none of the specialist herbivores or diseases from their native range, giving them a competitive advantage over native plants ("Enemies Hypothesis"). In order to test the Enemies Hypothesis, we transplanted native and alien tree seedlings into a number of habitats in East Texas, manipulated enemies and measured growth and survival of seedlings. We transplanted 240 seedlings of a native tree species, Celtis laevigata (Hackberry) and 240 seedlings of the invasive alien tree species Sapium sebiferum (Chinese Tallow Tree) into mesic forest, floodplain forest, coastal prairie and Sapium forest sites. We manipulated fungal diseases (foliar fungicide applications) and insect herbivores (foliar insecticide applications) in a full factorial design (species by site by fungicide by insecticide) with 15 replicates. The amount of fungal disease was low and exclusion of fungal diseases had no significant effect on the growth or survival of either tree species. Insect herbivores caused significantly greater damage to untreated C. laevigata than to untreated S. sebiferum but the removal of insect herbivores caused significantly greater increases in survivorship and growth for S. sebiferum than for C. laevigata. This suggests that greater chronic insect herbivory on natives does not facilitate the invasion of this alien species.

Keywords: Enemies Hypothesis

This abstract is being presented at: 8:00 AM in session:
Oral Session #26: Invertebrate Herbivore - Plant Interactions.