Predator-parasite links are common in food webs. I posted previously about how ontogenetic specialists (e.g., many parasites) increase food web connectivity, but decrease stability. That is, when you consider a species that requires different resources at different life stages as multiple “units,” instead of lumping all of the life stages together, the properties of the food web change.
When I posted before, I was really thinking about the resources of the “ontogenetic specialists.” For a parasite species with a complex life cycle, those resources are the different host species. But what if instead of looking at the ontogenetic specialists’ resources, we look at their predators? Do different life stages get preyed on more than others?
Why, yes, yes they do! Thieltges et al. (2013) classified predator-parasite links from eight food webs into one of three categories: concomitant predation, trophic transmission, and predation on free-living parasite stages. Briefly, concomitant predation occurs when a parasite living in a host gets consumed along with its host by a predator, and the parasite is digested. Trophic transmission occurs when a parasite living in a host gets consumed along with its host by a predator, and the parasite successfully establishes in the predator. And predation on free-living parasite stages is just that – the parasites are being consumed when they are not in a host. For trematodes, these free-living stages are eggs, miracidia, and cercariae. (I mentioned previously that larval trematodes can be abundant in zooplankton communities, and may therefore represent a lovely food resource for aquatic predators.)
Break down of predator-parasite links in eight aquatic food webs. Mmm, parasite pie.
Turns out that concomitant predation is the most common predator-parasite link. Neat! There’s more cool stuff in the paper, but I’ll leave it to you to go check it out.
Have you seen this done elsewhere for other ontogenetic specialists? For instance, do we expect larval organisms (e.g., tadpoles, larval insects, etc.) to be preyed on more than adults?
Reference:
Thieltges, D. W., Amundsen, P.A., Hechinger, R. F., Johnson, P. T. J., Lafferty, K. D., Mouritsen, K. N., Preston, D. L., Reise, K., Zander, C. D. and Poulin, R. (2013), Parasites as prey in aquatic food webs: implications for predator infection and parasite transmission. Oikos.
Parasite Ecology 
Nice post! What do you think about the recent Dunne et al paper?
Oooh, thanks for the link! I hadn’t seen it yet! Lots of big names on that one. 🙂
I might end up posting about this, because I’ve been meaning to post about a related paper that I read a while back. In Dunne et al. (2013), they found that one of the ways that parasites are unique additions to foodwebs involves the fact that they eat things bigger than themselves, whereas free-living organisms tend to eat things smaller than themselves. This is a problem because we often use one-dimensional niche models of foodwebs, where we order things by body size, and organisms only eat things to the left of themselves on that axis. (I think.) In Warren et al. (2010) – link below – they developed an inverted niche model for foodwebs with parasites, where the “to the left” rule still applies to predators, but the rule is reversed for parasites.
I thought the Warren et al. (2010) paper was really cool, but I have to admit that most of it is over my head. 🙂 Maybe it’ll be more clear when I re-read it. Thanks for the inspiration!
Here’s a link to the PDF: https://labs.eemb.ucsb.edu/kuris/armand/pubs/Warrenetal2010TheorEcol.pdf
Thanks for the Warren et al paper. I look forward to any future post of yours on the subject!
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