Linking Ecology and Epidemiology: The Case of Infected Resource

Interspecific interactions in ecological communities are the main mechanisms that determine structure, functioning, and stability of ecosystems (May, 1972, 1973; Neutel et al., 2002; Alessina and Tang, 2012; Mougi and Kondoh, 2012, 2014). These interactions can be qualitatively positive, negative, or neutral, and pairs of these interactions between two species may be of opposite sign (e.g., trophic, parasitic) or of equivalent sign (e.g., mutualistic, competitive). Most of the research on ecological interactions has focused on feeding relations (Odum, 1971; Pimm, 1982; Levin et al., 2009; McCann, 2011; Moore and de Ruiter, 2012), but in recent studies of ecological communities this was extended to parasitic (Huxham et al., 1995; Thompson et al., 2004; Lafferty et al., 2006; Kuris et al., 2008) and non-parasitic non-trophic relations (Thebault and Fountaine, 2010; Fontaine et al., 2011; Kéfi et al., 2012; Mougi and Kondoh, 2012; Sauve et al., 2014). In this chapter, we focus on parasitic relations and notably on the question of how trophic interactions and infectious agents mutually influence each other. Here we will refer to the combined classes of infectious species as parasites (see next section for details). The impact of parasites in an ecological community can be quantified through their direct influence on the food-web structure, as well as more indirectly through the way they influence physiological traits of host species and trophic relations of the host and non-host species (Kéfi et al., 2012; Selakovic et al., 2014). In this chapter we first briefly discuss the diversity of parasitic interactions, their relationships with host and non-host species, as well as their effects on a simple consumer–resource relationship consisting of one host and one non-host species. The largest part of the chapter is devoted to exploring a basic model, to show how intricately ecological and epidemiological effects are interwoven, even in the simplest possible ecosystem consisting of two species. Even though this model is basic in the sense that it is low dimensional and not meant to realistically represent any particular system, the analysis does hint at broader ecological insight, for example into possible differences between terrestrial and aquatic ecosystems based on parasitic interaction. The simple analysis highlights the need to study the link between ecology and infectious disease epidemiology in more realistic models.