The role of hemiparasites in structuring ecosystems

Research Sponsored By: National Science Foundation (NSF)
Principal Investigator: Jonathan Bakker
Project Description
Hemiparasites are plants that are able to obtain resources both by making their own via photosynthesis and by stealing resources from the roots of other plants. Hemiparasites occur around the globe, have strong effects on ecosystems, and can be economically important. The goal of this research is to begin to understand how hemiparasites influence, and are influenced by, the host plants they parasitize and by the herbivores that feed upon them. While hemiparasitism and herbivory have been studied separately, few studies have examined them simultaneously to determine their relative importance. In addition, hemiparasites may serve as mediators in tri-trophic interactions where the host plants they parasitize indirectly affect the performance of herbivores that feed upon them. This relationship is intellectually intriguing as plants have rarely been observed in this mediator role. By tracking the movement of nutrients among organisms, this research will expand our knowledge of the mechanisms behind these interactions. Finally, this research has practical significance and will inform the management and recovery of two rare species: Castilleja levisecta (a hemiparasite; federally listed as threatened) and Euphydryas editha taylori (an herbivore; federally listed as endangered). This research will also provide research training to a post-doctoral research associate, a graduate student, and an undergraduate student technician. The organisms used in this study co-occur in grasslands of the Pacific Northwest US. Experimental mesocosms will be assembled that contain host plants, hemiparasites, and herbivores. Mesocosms will contain high or low numbers of plant species that can serve as hosts for hemiparasites. Hemiparasitism will be allowed to occur or not, and herbivores (Euphydryas editha, Autographa californica) will be allowed to feed on the hemiparasites in a subset of the mesocosms. Hemiparasite survival, biomass, and secondary chemistry will be measured to determine how they are affected by host community composition, and herbivore performance will be related to host plant community and to hemiparasite resources. Stable isotopes will be used to track fluxes of carbon and nitrogen from the host plant community to the hemiparasites, and through the hemiparasites to their herbivores. The results of this research will provide insight into trophic interactions that structure ecosystems.