CHAPTER TEN Is Infectious Disease Just Another Type of Predator - Prey Interaction ?

Which factors fundamentally separate infectious disease from other types of predatorprey interactions studied by community ecologists? Could parasitism and predation be combined into a unifying model? After all, parasites and predators both convert energy and nutrients contained in their resources (hosts or prey, respectively) into new biomass and reproductive work. If these focal consumers perform similar roles, disease ecologists and community ecologists may essentially study the same problems. Therefore, they should use the same conceptual toolkits. Given this important potential for more intellectual crossfertilization, we contemplate these questions by way of two arguments. First, we consider the case that parasitism and predation are essentially the same types of interactions, varying only quantitatively. This line of argument highlights the many similar ways in which parasites and predators interact with their resources and other species at local and macroecological scales. Perhaps, then, major differences between predators and parasites vary only quantitatively, as a matter of bodysize scaling. Parasites are typically much smaller than their host, while predators are similarly sized or exceed the size of their prey. The second case embraces eight (or more) qualitative splits that separate different types of predators from different types of parasites (developed by Lafferty and Kuris 2002). These axes differentiate consumers that eat one versus more than one resource individual per life stage, consumers that kill or do not kill their resources, and so forth. Both lines of argument eventually lead to the same challenge, however: Just how many qualitative models must one consider to capture the range from predation to parasitism in nature? The answer almost certainly depends on the focal question (implications for population dynamics, nutrient cycling, evolutionary change, etc.) and the currency used to evaluate it.