PARENT SESSION
Oral Session #55: Predator - Prey Interactions.
Presiding: R. Dueser
Wednesday, August 7. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Field evidence for a strongly cascading underground food web.

Preisser, Evan^*,1, ¹ University of California, Davis, Davis, CA

ABSTRACT- Argument exists over whether terrestrial predators generally suppress herbivores and produce trophic-level regulation of plant abundance. In grasslands, the nematode Heterorhabditis marelatus has the potential to suppress root-feeding larvae of the moth Hepialus californicus and facilitate lupine (Lupinus arboreus) growth and survival. I performed a field experiment where mature lupine bushes in eight plots had 24 early-instar moth larvae added to each bush's rhizosphere. Four plots had nematode predators added to the soil, while no nematodes were added to control plots. Indirect effects on lupine growth due to the nematodes appeared quickly. Lupine trunk growth increased 15% in predator treatments after two months, and 70% after eight months. Herbivore densities were halved in the predator treatments. Nematode enemies of these underground herbivores have an strong effect on plant growth, and this cascade occurred within a complex and largely unmanipulated food web. The strength of this terrestrial cascade is a result of the large per-capita effect of the root-feeding herbivores on their host plant combined with the high herbivore mortality that the nematode can cause. Lupines, through the release of N, allow non-native grasses to invade native grasslands. Through its effect of lupine size and survival, this biotrophic cascade may thus have profound impacts on coastal plant communities.

KEY WORDS: trophic cascade, food chain, underground herbivory