PARENT SESSION
Oral Session #46: Animal Community Ecology: Pools, Foodwebs, Structure. Presiding: D. Post.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas I.
Intraguild predation dampens the combined impact of Grammonota and Pardosa spiders on prey populations.
Mitter, Margaret1, Langellotto, Gail2, Denno, Robert2, 1 2
ABSTRACT- There is growing evidence that interactions between natural enemies can affect the influence predators have on herbivorous insect prey and therefore modify the strength of top-down control of herbivore populations. However, the nature and magnitude of such higher-order interactions and their contribution to the balance between top-down and bottom-up control have rarely been examined in detail. We present an assessment of the interaction between a generalist hunting spider (Pardosa littoralis) and a much smaller web builder (Grammonota trivitatta) in a simple salt-marsh community dominated by Spartina alterniflora and its chief herbivore, the planthopper Prokelisia dolus. In laboratory mesocosm experiments, the rates of apparent predation on planthoppers for the two predators alone (one Pardosa versus five Grammonota) were approximately equal, whereas the predation rate with both predators present was only slightly, though consistently, higher. Predation by Pardosa on Grammonota was much more intense than cannibalism in the latter, particularly at low planthopper densities, consistent with intraguild predation as the mechanism underlying the non-additivity of predation rates. These results have important implications for diminishing trophic cascades and using multiple spider species in the biological control of agricultural pests.
KEY WORDS: intraguild predation, top-down control, spider predation, biological control