Print PageExotic herbivores often co-occur at high densities with exotic plants in eutrophic aquatic ecosystems, which can be a respond to nutrient enrichment, common dispersal pathways, or the interactions between native and exotic species or the interactions amongst exotic species. The effect that exotic species establishment have on food web structures often focuses on a single trophic level or is unknown. In this study, we investigated the effects of exotic herbivory on native and exotic aquatic plants and whether different nutrient levels affects the plant-herbivore interactions using common native and exotic species from southeastern Texas. Ninety-six 19-liter containers were assigned three treatments in a factorial design: exotic herbivore [presence or absence of Pomacea insularum (island apple snails)], plant identity [exotic {Eichhornia crassipes (water hyacinth), and Alternanthera philoxeroides (alligator weed)}, or native {Limnobium spongia (frog’s bit), and Hydrocotyle umbellata (water pennywort)}], and nutrient addition [zero, low, or high].
Results/Conclusions
We collected data on plant biomass and exotic herbivore size after 6 weeks. Exotic herbivory reduced plant biomass indicating that plants were herbivore limited. The exotic herbivore increased in size as nutrients levels increased suggesting that most of the nutrient addition energy was transferred up the food web. Exotic plants outperformed native plants regardless of nutrient levels and herbivory suggesting that exotic plants are more tolerant to changing environmental conditions compared to native plants, which would contribute to a higher probability of exotic plant establishment in inhospitable habitats for native species. These results suggest that the high abundance of exotic herbivores and plants in high nutrient conditions may be result of indirect positive effects of nutrients on snails and the higher tolerance of exotic plants to different environmental conditions.
