Abstract
Several studies failed to find strong relationships between the biological and ecological features of a host and the number of parasite species it harbours. In particular, host body size and geographical range are generally only weak predictors of parasite species richness, especially when host phylogeny and sampling effort are taken into account. These results, however, have been recently challenged by a meta-analytic study that suggested a prominent role of host body size and range extent in determining parasite species richness (species-area relationships). Here we argue that, in general, results from meta-analyses should not discourage researchers from investigating the reasons for the lack of clear patterns, thus proposing a few tentative explanations to the fact that species-area relationships are infrequent or at least difficult to be detected in most host-parasite systems. The peculiar structure of host-parasite networks, the enemy release hypothesis, the possible discrepancy between host and parasite ranges, and the evolutionary tendency of parasites towards specialization may explain why the observed patterns often do not fit those predicted by species-area relationships.
Highlights
The species-area relationship (SAR), that is, the increase of species number with area, is one of the best-documented patterns in ecology [1, 2], yet it is debated if this relationship should follow a universal shape or if different systems should have different SAR models [3]
Extending these concepts to host-parasite systems, we can assume that hosts with broader distributions have greater chances to be reached by a larger number of parasite species, which should lead to a positive relationship between host range size and associated parasite diversity (parasite-host range relationship (PHrR))
In-line with the parallelism between host-parasite and species-area relationships, one may speculate that hosts with large niche breadths should show a high parasite richness, due to the fact that they use a great variety of BioMed Research International habitats and are exposed to a wide diversity of potential parasites
Summary
Several studies failed to find strong relationships between the biological and ecological features of a host and the number of parasite species it harbours. Host body size and geographical range are generally only weak predictors of parasite species richness, especially when host phylogeny and sampling effort are taken into account. These results, have been recently challenged by a meta-analytic study that suggested a prominent role of host body size and range extent in determining parasite species richness (species-area relationships). In general, results from meta-analyses should not discourage researchers from investigating the reasons for the lack of clear patterns, proposing a few tentative explanations to the fact that species-area relationships are infrequent or at least difficult to be detected in most host-parasite systems. The peculiar structure of host-parasite networks, the enemy release hypothesis, the possible discrepancy between host and parasite ranges, and the evolutionary tendency of parasites towards specialization may explain why the observed patterns often do not fit those predicted by species-area relationships
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