PARENT SESSION
Symposium #13: Trophic cascades in complex and simple terrestrial systems.

Organized by: MD Moran and WE Snyder
Tuesday, August 6. 1:00 PM to 4:30 PM. Crystal Ballroom, TCC.

Scale, non-equilibrium, and subsidy of a trophic cascade.

Strong, Donald^*,1, Dugaw, Chris¹, Hastings, Alan, Preisser, Evan, ¹ Section of Evolution and Ecology, Davis, CA, 95616

ABSTRACT- Classical work has revealed the natural variability of trophic cascades: on fairly fine scales, in equilibrium contexts, and in the biotrophic channel. We have studied a powerful, yet apparently unstable, biotrophic cascade. Entomopathogenic nematodes kill root-feeding caterpillars and thus protect bush lupine (with profound ecosystem and biodiversity consequences). However, these nematodes have a high extinction rate in the semi-isolated lupine rhizospheres. They suffer heavily from soil dryness and natural enemies. Non-linear interactions with hosts could contribute to local extinctions. Without protection of the nematode, caterpillars can severely harm and kill lupine; patches of the bush spanning hundreds of meters can die as a result of underground herbivory. Lupines, the insects, and the microparasite wax and wane across the coastal grassland. Beyond patches of lupines, the nematode exists over a broad area of the Pacific Coast, and preys upon many other insect species. We explore the idea that the fine- existence of the cascade (within rhizospheres) is owing to a coarser grained saprotrophic subsidy. We posit that the original colonization of lupine rhizospheres by nematode populations, as well as their rescue from local extinction, is via nematode immigrants from detritivorous insects in the surrounding grassland. This example illustrates how scale, stability, and subsidy can contribute to an understanding of trophic interactions.

KEY WORDS: foodweb, trophic cascade, underground, entomopathogenic