Karthik Ram

The role of microparasites in grassland food webs

Predator-prey interactions play an important role in regulating the structure and dynamics of food webs. Other types of natural enemies such as parasites, pathogens and parasitoids also play equally important roles in certain communities but little is known about how dynamics of those interactions differ from ones mediated by predators. For my dissertation I studied the ecology of a subterranean parasite in the context of a terrestrial trophic cascade.

In California’s coastal prairie, a microparasitic entomopathogenic nematode Heterohabditis marelatus is the natural enemy of the ghost moth (Hepialus californicus) larvae which are root feeding herbivores of the bush lupine (Lupinus arboreus). By suppressing ghost moths, entomopathogenic nematodes protect lupines and increase seed set, growth and survivorship. In their absence, ghost moths can decimate large stands of lupines and can potentially alter the composition of the plant community. Entomopathogenic nematodes are however, highly extinction prone due to dual abiotic and biotic stressors.

While at the University of California at Davis I examined various mechanisms to explain long-term persistence of an extinction prone parasite. Using a combination of experimental and observational data, I demonstrated mechanisms that allow for persistence of a parasite-mediated trophic cascade (10.1007/s00442-010-1844-5) (19259524). In collaboration with Chris Dugaw, I also developed a novel statistical model to incorporate individual heterogeneity in estimates of mortality (10.1890/08-0228.1)

Ghost moths feeding inside a lupine stem.

Lupinus arboreus form dense, monospecific stands across the reserve. This picture was taken during a particularly wet year.

I carried out this research as part of my PhD with Don Strong in the ecology graduate group at UC Davis.