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.
Disturbance underlies spatial variation in the strength of top-down and bottom-up control of insect herbivores.
Denno, Robert1, Gratton, Claudio1, Langellotto, Gail1, Huberty, Andrea1, Finke, Deborah1, 1
ABSTRACT- An increasing number of studies have shown the simultaneous effects of both plant resources and natural enemies on the population dynamics of herbivorous insects. Thus, top-down and bottom-up forces typically act in concert in most systems. What is poorly understood is habitat-related variation in the strength of bottom-up versus top-down control and the factors that underlie such spatial variation. Using an experimental approach in a model salt-marsh system, we explored spatial variation in the relative contribution of host plant resources (plant quality and structural complexity) and invertebrate predators (wolf spiders) on the population dynamics of Prokelisia planthoppers. In low marsh habitats characterized by frequent tidal inundation, planthopper dynamics are driven largely by the bottom-up effects of plant nutrition because natural enemies are rare. By contrast, invertebrate predators are more abundant in high marsh habitats and top-down control of planthopper populations is stronger. Thus, tidal disturbance appears to dictate the relative strengths of top-down and bottom-up control in this planthopper dominated system.
KEY WORDS: disturbance, predation, herbivory, flooding