The role of specialist parasites in structuring host communities |
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Authors: | Andy Fenton Michael A Brockhurst |
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Institution: | (1) School of Biological Sciences, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK |
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Abstract: | Natural enemies can be a powerful force when structuring natural communities, and in facilitating or preventing species coexistence
depending on the nature of the trophic interaction. In particular, “keystone” predators can promote species coexistence, provided
they preferentially attack the competitively dominant species. However, it is not clear whether parasites can play a similar
structuring role; parasites typically form chronic associations with their victims, reducing their fitness (i.e., fecundity)
rather than survival, and allowing infected hosts to remain viable competitors within the community. Therefore the density-dependent
suppression of the host is likely to be more subtle than that due to predation. Using a series of simple population-dynamic
models we show that specialist parasites can facilitate species coexistence, although possibly less so than predators. These
results contrast with those typically found with models of generalist parasites, which can reduce the likelihood of species
coexistence through apparent competition. In addition, we show that the likelihood of parasite-facilitated species coexistence
depends greatly on the specific type of parasite. In particular, macroparasites (e.g., parasitic helminths) may be less likely
to facilitate species coexistence than microparasites (e.g., viruses or bacteria) due to their typically highly aggregated
distribution amongst their hosts. Furthermore, species coexistence is more likely if the parasite is relatively benign to
its host. Parasitism by apparently “harmless” specialist parasites may provide an important but overlooked factor in the maintenance
of species diversity, facilitating species invasions into new communities and the emergence of novel infectious diseases. |
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Keywords: | Apparent competition Competitive exclusion Keystone predator Resource competition Species coexistence |
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