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Food web structure of three guilds of natural enemies: predators, parasitoids and pathogens of aphids


Van Veen, F J F; Müller, C B; Pell, J K; Godfray, H C J (2008). Food web structure of three guilds of natural enemies: predators, parasitoids and pathogens of aphids. Journal of Animal Ecology, 77(1):191-200.

Abstract

1. Most communities of insect herbivores are unlikely to be structured by resource competition, but they may be structured by apparent competition mediated by shared natural enemies.
2. The potential of three guilds of natural enemies (parasitoids, fungal entomopathogens and predators) to influence aphid community structure through indirect interactions is assessed. Based on the biology, we predicted that the scope for apparent competition would be greatest for the predator and least for the parasitoid guilds.
3. Separate fully quantitative food webs were constructed for 3 years for the parasitoid guild, 2 years for the pathogen guild and for a single year for the predator guild. The webs were analysed using standard food web statistics designed for binary data, and using information-theory-based metrics that make use of the full quantitative data.
4. A total of 29 aphid, 24 parasitoid, five entomopathogenic fungi and 13 aphid specialist predator species were recorded in the study. Aphid density varied among years, and two species of aphid were particularly common in different years. Omitting these species, aphid diversity was similar among years.
5. The parasitoid web showed the lowest connectance while standard food web statistics suggested the pathogen and predator webs had similar levels of connectance. However, when a measure based on quantitative data was used the pathogen web was intermediate between the other two guilds.
6. There is evidence that a single aphid species had a particularly large effect on the structure of the pathogen food web.
7. The predator and pathogen webs were not compartmentalized, and the vast majority of parasitoids were connected in a single large compartment.
8. It was concluded that indirect effects are most likely to be mediated by predators, a prediction supported by the available experimental evidence.

1. Most communities of insect herbivores are unlikely to be structured by resource competition, but they may be structured by apparent competition mediated by shared natural enemies.
2. The potential of three guilds of natural enemies (parasitoids, fungal entomopathogens and predators) to influence aphid community structure through indirect interactions is assessed. Based on the biology, we predicted that the scope for apparent competition would be greatest for the predator and least for the parasitoid guilds.
3. Separate fully quantitative food webs were constructed for 3 years for the parasitoid guild, 2 years for the pathogen guild and for a single year for the predator guild. The webs were analysed using standard food web statistics designed for binary data, and using information-theory-based metrics that make use of the full quantitative data.
4. A total of 29 aphid, 24 parasitoid, five entomopathogenic fungi and 13 aphid specialist predator species were recorded in the study. Aphid density varied among years, and two species of aphid were particularly common in different years. Omitting these species, aphid diversity was similar among years.
5. The parasitoid web showed the lowest connectance while standard food web statistics suggested the pathogen and predator webs had similar levels of connectance. However, when a measure based on quantitative data was used the pathogen web was intermediate between the other two guilds.
6. There is evidence that a single aphid species had a particularly large effect on the structure of the pathogen food web.
7. The predator and pathogen webs were not compartmentalized, and the vast majority of parasitoids were connected in a single large compartment.
8. It was concluded that indirect effects are most likely to be mediated by predators, a prediction supported by the available experimental evidence.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Uncontrolled Keywords:Coccinellidae, Entomophthorales, keystone, phytophagous, Syrphidae
Language:English
Date:January 2008
Deposited On:11 Feb 2008 12:28
Last Modified:05 Apr 2016 12:21
Publisher:Wiley-Blackwell
ISSN:0021-8790
Additional Information:Author Posting. © The Authors 2008. The full text of this article is published in Journal of Animal Ecology, Vol. 77 (1) 191-200 p.. It is available online from Blackwell-Synergy at http://dx.doi.org/10.1111/j.1365-2656.2007.01325.x. Note: N.B.The full text of the Article will be made freely available via Blackwell-Synergy 2 years after publication
Publisher DOI:10.1111/j.1365-2656.2007.01325.x

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