PARENT SESSION
Poster Session #4: Invasions.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

The role of native generalist herbivores in Chinese Tallow Tree (Sapium sebiferum) invasions into coastal prairie.

LANKAU, RICHARD¹, SIEMANN, EVAN ¹, ROGERS, WILLIAM¹, ¹

ABSTRACT- Alien plants may have a competitive advantage over native plants because native herbivores may feed less on the alien plant compared to native plants. To test this hypothesis, we enclosed three densities (none, field density, and twice field density) of native Acridid grasshoppers (Melanoplus angustipennis and Orphullela pelidna) in a Texas coastal prairie. Each enclosure contained native prairie vegetation and a seedling of either the alien Sapium sebiferum (Chinese Tallow Tree) or the native tree Celtis laevigata(Hackberry). Sapium sebiferum is a major invader of many ecosystems in the southeast United States. Celtis laevigata is common in coastal prairies. Contrary to predictions, Sapium suffered significantly more chewing damage than Celtis at both densities of grasshoppers. Only the final aboveground mass of Sapium seedlings decreased significantly with increasing grasshopper density. Neither Celtis seedling mass or aboveground community biomass depended on grasshopper density. Melanoplus angustipennis grasshoppers preferred Sapium sebiferum foliage over the foliage of Celtis laevigata, Liquidambar styraciflua (sweetgum), and Platanus occidentalis (sycamore) in laboratory feeding trials. These results suggest that differential herbivory by native herbivores may not be a factor in Sapium's invasion. The lack of support for the assumptions of "Enemies Hypothesis" in this experiment requires alternate explanations for the invasive success of this species.

KEY WORDS: species invasions, Sapium sebiferum, generalist, herbivory