Does anyone have an example of a parasite species where the non-parasitic life stage(s) hold a key location in the ecosystem, not related to the host, where elimination of the parasite could cause an ecological cascade?
I know that, theoretically, elimination of a parasite might cause a host population to increase unchecked, which in turn could have cascading effects on other trophic levels, competitors of the host, etc. And there might actually be real-world examples of this.
BUT, what I am looking for is an example where elimination of the parasite causes an unrelated cascading effect (for example, if elimination of screwworms (Diptera: Calliphoridae) might cause a plant species to decline because adult screwworms were no longer present to pollinate the plants.)
The only example I've seen so far is Wyeomyia smithii mosquitoes in North American pitcher plants. They function as a key member of the tiny, close-knit intra-pitcher plant community, where they feed on organic detritus left by the Metriocnemus knabi midges, making nitrogen available to the plants. But there are also many other microorganisms (rotifers, bacteria, protozoa) present that could potentially fill the niche left if Wyeomyia were eliminated. Plus, Wyeomyia adults are only facultatively parasitic.
Parasites act as ecosystem engineers, alter energy budgets and nutrient cycling, and influence biodiversity. pollinators – that have clear positive effects within ecosystems. However, parasites – usually regarded in terms of their detrimental effects on the individuals they infect – can also have positive impacts on other species in the community. We now recognize that parasites influence species coexistence and extirpation by altering competition, predation, and herbivory, and that these effects can, in turn, influence ecosystem properties. Parasites and pathogens act as ecosystem engineers, alter energy budgets and nutrient cycling, and influence biodiversity. Equally, because ecosystem properties – such as biodiversity – affect parasite populations, there is the potential for feedback between parasitism and ecosystem states.
Yes, Sunday J Kekrula , agreed, but those are secondary effects of the parasite as a result of it parasitizing its host. What I am asking is examples of a parasitic species NOT acting as a parasite and effecting all the downstream ecosystem services because of that trophic role, but as a different trophic level - AND where it functions in a more-or-less keystone fashion where its presence/absence would make a significant ecological difference.
See my example in the question: Wyeomyia mosquito larvae function as filter-feeders (not as parasites) in the pitcher plant community; their absence alters the rotifer, bacteria, and protozoan communities, and it is unknown if it affects the nutrition of the pitcher plants. Although adult Wyeomyia can function as parasites, the larvae are not functioning as parasites but still hold a significant position in the community.
I'm looking for examples like that one.
What I am NOT looking for:
- Parasites affect their hosts, which in turn affects predation or herbivory or pollination services by the hosts, which in turn affects lower trophic levels through reduced mortality, higher trophic levels through feedback mechanisms, or the same trophic level through reduced competition. These are all secondary effects of being parasites.
- Parasites like mosquito larvae are fed upon by other organisms. True, but they are generally redundant with chironomids, chaoborids, corixids, etc., So their absence would probably not make a significant ecological difference.
By the way, I did find another possible example: Horse guard wasps in the genus Stictia (Hymenoptera: Crabronidae) prey preferentially on tabanids, which are parasites. They seem to do a good job at controlling horse fly populations, so I wonder if removing horse flies would have an effect on the Stictia population or if they would switch to preying on other flies (as they already do facultatively).
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