Food webs and parasites in a salt marsh ecosystem

Our mothers teach us to grill our meats " well done " and chew them thoroughly. Even if mom did not know why she insisted, both are good precautions against parasites. Parasites may be in our food, but they are not in our food webs. Is it necessary to take the precaution of considering them? In this chapter, we argue that parasites affect important properties of food webs and that it may be difficult to fully understand ecosystems without considering parasites. Food webs depict trophic interactions among networks of consumers, producers, and non-living material. Units in food webs range from specific life-cycle stages of species to broad taxonomic/ functional groups. At the most basic level, food webs are static diagrams or matrices of who eats whom (topological webs). Some food webs track flows of energy and matter among links (bioenergetic webs). Other food webs denote the strengths of interactions among species (interaction webs). The food-web framework captures much of the current theory on how habitat heterogeneity, species richness, trophic cascades, indirect mutualism, apparent competition, intraguild predation, environmental change, ecosystem stability, nutrient dynamics, and productivity affect community structure (Paine 1988; Winemiller and Polis 1996). Food webs also aid applied research by providing a better understanding of pest control, environmental contamination, bioremediation, and fisheries management (Winemiller and Polis 1996). Published food webs vary considerably in quality and detail, but nearly all exclude consumers that are not readily detectable, such as endoparasites and other infectious agents (Polis 1991; Cohen et al. 1993). Indeed, perhaps because they are difficult to detect, typical parasites have been historically lacking from the bulk of ecological theory. However, parasitism is arguably the most prevalent lifestyle among animals (Price 1980; DeMeeûs and Renaud 2002). As ecolo-gists increasingly consider the role of parasites in ecosystems, it is becoming clear that parasites are embedded in food webs and may need to be considered in food-web theory (Polis 1991; Cohen et al. Incorporating parasites, as we have done here, helps illuminate the role of parasitism in natural communities (Dobson et al. 2005), and reveals how changes in community structure may affect rates and patterns of parasitism. Almost all published food webs describe predator– prey links (e.g. lion–gazelle–grass). Food webs of insect parasitoids and their hosts have also been developed because parasitoids are relatively easy to observe when they emerge from their hosts (Lawton 1989). The full food web in any given community …