PARENT SESSION
Oral Session #9: Trophic structure and community interactions. Presiding: B. Menge.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.

Interseasonal carryover of a fertilization pulse on populations of an insect herbivore and its predators.

Gratton, Claudio¹, Denno, Robert ¹, ¹

ABSTRACT- The influence of variation in plant quality (bottom-up effects) on herbivore populations are often examined within a single generation of herbivores or among generations within a growing season. In this experiment, we monitored the potential for among-year carryover effects of a single pulsed fertilization of meadows of salt-marsh cordgrass, Spartina alterniflora on the population dynamics of Prokelisia planthoppers. Foliar nitrogen remained elevated in Spartina plants for at least 2 years after the initial fertilization. In addition, plant biomass and accumulated dead biomass was higher in fertilized plots at least two years post-fertilization. Similarly, the initial fertilization resulted in enhanced adults planthopper densities within the same growing season. In addition, planthopper populations were significantly greater in fertilized plots compared to unfertilized plots for at least two years post-fertilization. The same pattern was also seen for predators, including hunting and sheet-building spiders and mirid egg predators. These results suggest that even single perturbation of basal resources of food webs may have strong and persistent effects on herbivore and predator densities in salt marsh ecosystems.

KEY WORDS: herbivory, food web, bottom-up, salt-marsh