Submitted to: Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/11/2007
Publication Date: 6/3/2008
Citation: Grewell, B.J. 2008. Parasite facilitates plant species coexistence in a coastal wetland. Ecology. 89(6): 1481-1488. Interpretive Summary: This manuscript will be submitted for publication in Ecology, the Ecological Society of America's primary scientific journal. The audience will include professional ecologists, conservation and restoration practitioners and scientists in academia and government agencies. While there has traditionally been a negative view of parasites due the virulence of parasite-transmitted diseases of humans, native parasite species are increasingly recognized as important players that maintain ecological balance in some natural communities. Parasitic plants are common in natural ecosystems and many are crop pests. Parasite-host interactions are thought to be a major force in generating biological diversity and can play an important role in food web and ecosystem dynamics, yet rigorous field experiments to test the effects of parasite-host interactions and community response are few. In this study, I recorded field observations of host preference and infectivity of Cuscuta to determine if (a) potential hosts are equally infected, (b) Cuscuta infection pattern changes over time, and (c) there are differences in infectivity among hosts. In order to examine the virulent impact of Cuscuta on its preferred host and potential indirect effects on the salt marsh community, I manipulated the abundance of Cuscuta in a fully randomized removal experiment in a natural field setting. Results demonstrate a continuum of negative to positive effects of Cusuta. The parasite showed a strong host preference, and priority effects enhanced suppression of a community dominant host species while species richness and rare plant fitness were the indirect beneficiaries of the interaction. Results suggest parasitism can strongly influence plant community structure. Understanding the role Cuscuta might play in changing processes that influence the course of succession has applied significance in restoration ecology, and may be useful in the prediction and management of restoration trajectories.
Technical Abstract: Recent advances in ecology suggest that processes influencing community structure are a balance between competitive and facilitative biological interactions. Parasitic angiosperms are prevalent in many North American and European coastal salt marshes, and consumer-resource interactions between parasitic plants and their hosts may also drive local community dynamics. I examined host identity and temporal variation in host infectivity of the holoparasitic vine (Cuscuta salina) within a California salt marsh. In a two year parasite removal experiment, I measured the effect of Cuscuta on its most frequent and highly infected host (Plantago maritima), a rare hemiparasite (Cordylanthus maritimus ssp. palustris), and the salt marsh plant community. Cuscuta clearly suppressed its preferred host and rare plant fitness and plant species richness in the community were enhanced through indirect effects. Priority effects played a role in the strength of the effect due to the timing of host life history characteristics. The differential influence of interplant parasitism on host plant fecundity may change population dynamics, benefit rare species, and alter salt marsh community structure. The continuum of negative to positive consequences of parasitic interactions deserves more attention if we are to understand tidal wetland community structure and successfully restore functional salt marsh communities.