[henearkr]

We might even one day deem essential some parasitic worm when find it's the only mitigation against another animal regarded as a pest. Actually there are many cases in the natural environment where parasites like this are the vector limiting overpopulation. So eradicating the parasite could lead to resources depletion and extinction of the host species, or make disappear other species they feed on, etc.

[qchris]

I genuinely don't know the answer: is there another word for this concept, where a parasite benefits the species as a whole, but not the individual? That would seem to be a form of symbiosis, not parasitism.

>> there are many cases in the natural environment where parasites like this are the vector limiting overpopulation

Can you provide a couple of examples? I'd be interested in looking into this further to see how that works. Obviously, predators are a different category, and fill an important niche in the ecosystem, but I was unaware that species classically considered "parasites" performed a similarly important role. For example, ticks on moose seem very different from wolves hunting them.

[henearkr]

Here is the entry point that I read recently:

https://phys.org/news/2020-08-parasites-important.html

This is the link above which made me overconfident to easily find on the web many examples of such natural regulations. But I could not find a lot... what is more easy to find is mathematical studies showing the effect on populations.

Here is one study considering the potential implications of parasites eradication:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5222570/

For some particular examples, the red grouse is a bird whose population follows periodic cycles, and the cause is a parasite. Removal of the parasite smoothed out the population variations. You can imagine other species (plants or animals) whose own population cycles would be adapted to the old cycles, and these species would be impacted by the smoothing out of red grouses.

Link: https://www.jstor.org/stable/4694?seq=1

More generally, when a parasitic regulation disappears, the next in line would be resources regulation, that is the species starves when the food is scarce, and thus the population plummets. That could lead to a very different population dynamics (as the red grouse example shows, but there can be situations where the graph is sharpened instead of dampened like here), and because of that one or several species can disappear.

[qchris]

Hmmm, that's really interesting! Thanks for digging into it a little more and posting these resources :)