Abstract
This review explores some of the reasons why food webs seem to contain relatively few parasite species when compared to the full diversity of free living species in the system. At present, there are few coherent food web theories to guide scientific studies on parasites, and this review posits that the methods, directions and questions in the field of food web ecology are not always congruent with parasitological inquiry. For example, topological analysis (the primary tool in food web studies) focuses on only one of six important steps in trematode life cycles, each of which requires a stable community dynamic to evolve. In addition, these transmission strategies may also utilize pathways within the food web that are not considered in traditional food web investigations. It is asserted that more effort must be focused on parasite-centric models, and a central theme is that many different approaches will be required. One promising approach is the old energetic perspective, which considers energy as the critical resource for all organisms, and the currency of all food web interactions. From the parasitological point of view, energy can be used to characterize the roles of parasites at all levels in the food web, from individuals to populations to community. The literature on parasite energetics in food webs is very sparse, but the evidence suggests that parasite species richness is low in food webs because parasites are limited by the quantity of energy available to their unique lifestyles.
Highlights
Over the last decade, there has been an enormous increase in the number of publications dealing with parasites and food webs, and there is no longer the need to argue that parasites must be included in all models of ecosystem function
On the other hand, when parasitologists think about food webs, they are primarily interested in the characteristics of the food web that allow successful colonization by parasites, and the ecological processes that contribute to the evolution of parasite life cycles and transmission pathways
In conclusion, this review posits that traditional food web approaches based on topological analyses do not take into account all aspects of parasite life cycles
Summary
There has been an enormous increase in the number of publications dealing with parasites and food webs, and there is no longer the need to argue that parasites must be included in all models of ecosystem function. Since only binary data is required, the technique makes it easier to quantify large scale ecological phenomena related to the effects of habitat destruction; species extinctions, alien invasions, and infectious disease epidemiology [93,94,95] These areas of research on food webs are not discussed much in this review because most of these studies do not include parasites in their analyses, this situation is changing as more parasitologists join the field [4,96]. These results, and the results of other network-based analyses that include parasites [53,54,114] suggest that highly connected free-living species interacting within core modules may represent stable trophic relationships that allow for the persistence of complex parasite life cycles [24] These results supports the notion that the topological structure of host food webs can have a significant effect on the establishment of parasites, and on the potential for evolution of complex parasite life cycles.
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