There are many ways to eat leaves, too, though. A leaf miner is not a caterpillar or a grasshopper.
My nutrition ecology class back in the day presented a graph to help understand feeding strategies. Let’s see if I can draw an XY graph with text (ignore the row with column labels).
| Column 1 | Column 2 | Column 3 | Column 4 |
|---|---|---|---|
| L | |||
| E | |||
| T | PREDATOR | PARASITOID | |
| H | |||
| A | |||
| L | |||
| I | BROWSER | PARASITE | |
| T | |||
| Y | |||
| SPECIFICITY |
How are “crop” and “pest” biological terms independent of anthropocentric activity?
Well, with that definition, “in the general sense” every word is biological/scientific.
Not that I agree, but aren’t you denying here something that you allowed for yourself earlier? By your definition, “pest”, “crop”, and “parasite” should all have equal scientific standing in some “broad/general” sense.
But anyway: the point is, your original claim was that:
which is clearly false, since (however loosely you choose to define your terms), not all aphids are pests. They are all plant-parasites, though - along with whiteflies, scale-insects and psylloids amongst the hemiptera. Presumbly this is why the iNaturalist taxonomy uses “Plant-parasitic hemipterans” as a common name for the suborder Sternorrhyncha.
Thank you for the discussion, as it represents the quintessence of a scientific approach. I base my comments on my education and the fact that I was once a scientist at the Institute of Parasitology of the Polish Academy of Sciences, so I think I know a thing or two about this topic…
An appeal to personal authority is the antithesis of the scientific method.
Surely parasite and pest are on unrelated axes? A species could be a parasite and a pest. Parasite refers to feeding strategy and pest refers to its influence on human activities.
I’m not an authority, I’m simply referring to what I’ve been taught. Best regards…
Of course, yes; best regards…
Scientific discussion or semantic squabbling? Everyone knows what is a pest or a predator and each is judged by its context. If the science can’t deal with that then the science needs to reconceptualise - or be forced into endless controversy. When analogue music performances are digitised then the ‘bits inbetween bits’ get lost; that’s the gap which is missing in the science. Perhaps an unresolvable question which will remain in the realm of philosophical enquiry (freeze v flux) rather than biology.
In the meantime, I will use my own judgement!
Sorry for the delay folks, just seeing this (I’m the manager of Who Eats Whom). Thanks for this generative and interesting discussion, I love getting to read the community’s thoughts on this sort of thing. There are so many interesting edge cases with feeding. This forum post was inspiration for me to finally prioritize making a document where the community can add/consider/ideate on such cases as these to inform way to improve Who Eats Whom data quality down the line. You can read and add to/comment on (please do so!) that document here: https://docs.google.com/document/d/12jrTgabnckUfi-5j5Ipdi2Tn05kEIIkuZ1ggU15Qdrw/edit?usp=sharing
To the specific questions raised here: I went ahead and modified the definition of “parasitism” to include sap-sucking as I think it fits the spirit of that category. I don’t think “classic” examples of herbivory like a buffalo eating grass should be included in “parasitism” even if the buffalo is only eating a part of the grass. Otherwise, just about any feeding interaction with a plant would be parasitism, which doesn’t seem like a useful way to parse things. @twainwright makes a good point about the awkardness of the word “pollination” as a type of feeding interaction, something I bring up in the document. I’m not sure what a better word would be though I welcome suggestions.
Some good discussion of commensalism, mutualism etc. here but I think that is sort of downstream of my goal with these categories (which are more focused on the mechanism of interaction between individual organisms (blood drinking etc.) than the fitness value of the interaction at the species/population level. Though there is obvious squishiness here (parasitism can be considered a mechanistic category and an evolutionary category).
I think classifying organisms as pests/not pests is probably beyond the scope of this project.
In what way is sap sucking “parasitism” but grazing is not?
Pollination – maybe use Nectaring & Gathering Pollen?
I can’t say there’s a fully logical reason why we classify grazing by buffalo is different from parasitism. In general, parasites are much smaller than their hosts, leaving the host looking about the same unless the host dies. Grazing and other things we classify as not parasitism usually do obvious, immediate damage to the plant and often involve an herbivore that is much larger that the victim, or at least larger than its leaves. Although I wouldn’t call that distinction fully logical, it is the one that we really do use.
I think one difference is that parasites/parasitoids (as normally defined) rely on the host as part of their immature development stage as both a source of food and as housing/protection. This relationship seems rather different in kind than sucking sap unless this activity causes the plant to engage in abnormal growth as a result of the damage (gall formation).
Admittedly, in some cases the distinction between parasitism and predation may become blurred – e.g. wasp species where the larvae develop by feeding on one or more specimens of another insect, either in the nest of that insect or in a nest built and provisioned by the wasp mother.
In that case fleas arent parasites then. Their larvae are free living detritivores. And the adults can freely switch between hosts and exist competently off their hosts
The formal definition of parasitism taught in parasitology classes (and in parasitology textbooks) is: an organism that lives on or inside an individual of another species and obtains nutrients from its host, harming (but not killing) it in the process. A buffalo is much larger than a grass plant and can’t live on it. A flea lives on a cat, but a buffalo doesn’t live on a grass plant.
If one ignores whether the organism is feeding on a plant vs. animal, the buffalo would best be considered a micropredator (like a cookiecutter shark, but eating plant tissue).
Here’s a relevant opinion piece:
Lafferty, K. D., & Kuris, A. M. (2002). Trophic strategies, animal diversity and body size. Trends in Ecology & Evolution, 17(11), 507-513.
Some species are, some aren’t. The ones which aren’t would normally be categorised as micropredators, rather than parasites. A key difference is the number of hosts. True parasites prey on only one host (although not necessarily the same host species) during each life-stage. Micropredators differ from more typical predators by being smaller than their hosts, and also by never killing them as a direct result of their feeding activity.
Aphids are parasites because they typically feed on a single host plant during each life-stage. The winged sexual generations can move on to new plants, but their asexual offspring stay put and feed only on the new host.
The specific feeding method is irrelevant. What really matters is the closeness of the relationship between the predator and the host. Any organism that moves from host to host whilst feeding (by whatever means) is not a parasite. But if an organism spends the entirety of one of its life-stages feeding on a single host (without killing it), it is a parasite. Of course, nature being what it is, there are many edge-cases that push the boundaries of these definitions, but the general principle holds true in enough cases for it to be useful.
I think number of hosts per life stage is an arbitrary distinguishing factor that doesnt as much on the animals biology as one thinks. For example, a tick and a scabies mite are parasites by this definition while a bedbug is a micropredator. But in by any practical measure a tick has far more in common in its lifestyle with a bedbug than a scabies mite. The tick and bedbug can both drop off/leave their hosts and function as free living animals that can disperse and navigate the world autonomously. A scabies mites entire existence is in the skin of its host.
I think the main problem this discussion runs up against is that definitions of parasitism suited to animal-animal interactions don’t transfer well to herbivory.