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In a relationship between two species, could a certain relationship become harmful to both involved species?

Keep in mind, I am looking for a relationship between two species, preferably of the kingdom animalia, although any example will aid my understanding. On an Earth-like planet, the known ecological relationships are predation, competition, mutualism, commensalism, amensalism and parasitism. I would imagine that any sort of relationship that involves both being harmed would not start directly as that relationship; it would evolve to that as a result of a parasitic or amensalistic relationship.

I can think of a few examples, such as a large horse-like animal that feeds on the same shrub as a small insect-like animal, which in turn gets ingested by the horse-like animal, and then attacks the horse-like animal from the inside. The end-game is that both parties are harmed. But I am looking for a relationship that is consistent and each of the parties is entirely aware of the relationship, but continues to engage in it.

If such a relationship could exist, how and why would it evolve to be like that?

As a side note, some of you might by gunning for me to mention neutralism, but I honestly don't care, it is a relationship that describes the lack of a relationship. Doesn't sound like much of a relationship to me. Please, no comments on neutralism.

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    $\begingroup$ The edit added the paragraphs; I should have added in my answer (or as a comment) that my enter key is not working. Thanks. $\endgroup$
    – blaizor
    Commented Jan 25, 2015 at 11:34
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    $\begingroup$ This table on Wikipedia syggests that this would be competition. There is also term synnecrosis seeming to describe your idea. By the way: If a parasite took too small host, the host would die and than the parasite would die. $\endgroup$
    – BartekChom
    Commented Jan 25, 2015 at 12:16
  • $\begingroup$ @BartekChom Indeed, the parasite would die. But I am looking for how a relationship would emerge from this, with both parties willingly engaging in the relationship even though they are aware the endgame is being harmed. Death is implied as a no-go. And competition is not the relationship I was looking for - certainly not intraspecies competition, in any case. The effects of competition aren't a directly handled relationship - any sort of animal doesn't choose to have another animal compete for its food. $\endgroup$
    – blaizor
    Commented Jan 25, 2015 at 12:20
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    $\begingroup$ Aware? Do you have a planet of sapient animals? The question doesn't make sense. Seems like any competition/predation with a defending prey situation could fit, if you removed the strange conscious awareness bit. $\endgroup$
    – user3652621
    Commented Jan 25, 2015 at 16:55
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    $\begingroup$ Look at evolutionary arms races. The classic example is the sabertooth (Smilodon). It attacked prey by biting the neck, so the prey with more protected necks survived to reproduce. This meant that the sabertooths (saberteeth?) with longer teeth were more successful at hunting, so prey with still better protected necks had the advantage. Eventually you wind up with absurdly long teeth and massively protected necks, both species ill-fitted for survival. $\endgroup$
    – jamesqf
    Commented Jan 25, 2015 at 18:58

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Something equivalent to the Prisoner's Dilemma might work.

If there are two behaviours to choose from for both parties which we might call "mean" and "nice" such that "mean" gives an advantage over "nice" regardless of the others behaviour, but both being "mean" is less desirable than being "nice" then the stable outcome (everyone mean) is harmful compared to the unstable ideal (everyone nice, but with a huge incentive to start being mean).

There are ways out of the prisoner's dilemma, but they require repeated interactions with memory of what happened in previous iterations. Within a population that's sufficiently small that you can recognize and remember individuals, this can work. Across species, it would be much harder to develop.

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  • $\begingroup$ The Prisoner's Dilemma. Of course. A brilliant example that combines with a strong yet concise explanation. Well thought through and well presented. Upvoted. $\endgroup$
    – blaizor
    Commented Jan 25, 2015 at 23:58
  • $\begingroup$ I wonder whether lion-elephant works as a real-world example. If they had the means to declare a truce, so that lions never hunt young elephants and in return older elephants don't drive lions away from e.g. water sources that they're currently using, then both species might benefit. Even so, a mutation that prevents lions hunting elephants only benefits the lions if they all get it at once and the elephants quickly learn that lions aren't a threat. This can easily fail to happen. $\endgroup$
    – Steve Jessop
    Commented Jan 26, 2015 at 13:33
  • $\begingroup$ That's an interesting one. I worked on the so called "iterated prisoner's dilemma" where you have memory of the past (and no visibility of the future, to avoid being mean on the last turn). Most global (group) winning strategies tend to be nice and reward cooperation. $\endgroup$
    – Uriel
    Commented Jan 26, 2015 at 23:09
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A clear example of a mutaully harmful relationship would be that of competition. Both groups of organisms compete for the same resource (eg water, food, sunlight) and both species suffer negative utility from the existence of the other organism. This can be observed all over the world.

As others have already mentioned, there is no sustainability in such a scenario, and this is an example of an unstable equilibrium. The two species will either:

1: Evolve into separate niches, which greatly reduces the issue of competition.

2: Have one species outcompete the other, resulting in the extinction of the less fit species

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I think Uriel hit upon how it could happen--while we can be slow to realize we are in a destructive relationship, evolution can be much slower to recognize this.

Thus picture a relationship that started out as a symbiotic relationship. Over the eons both sides of the relationship have evolved to exploit their partner to the point that both would be better off going it alone. However, the pairing behavior is programmed in and going it alone causes problems with attracting a mate, thus it's hard for it to evolve. (The odd animal that is born with a mutation that causes them to avoid the partner thrives but doesn't find a mate and thus doesn't pass on the mutation. To escape the trap you need not only the anti-partner mutation but one that removes whatever it is about the partner that's involved in mate attraction.)

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  • $\begingroup$ A simple yet effective answer. Uses other answers as resources and builds a strong foundation for a good understanding of how such a relationship would evolve. Upvoted, accepted. $\endgroup$
    – blaizor
    Commented Jan 25, 2015 at 23:09
  • $\begingroup$ I do not think evolution alone can lead to this situation, however, what could happen is a sudden context change with two symbiotic species that are now in a dead-end. Imagine a relationship where a previously common ressource was shared and vanishes, making organisms compete for it ? Water becoming rare, etc. $\endgroup$
    – Uriel
    Commented Jan 26, 2015 at 23:17
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There is no gain for any of the two species involved in such a mutually destructive relationship, so it wouldn't be a sustainable behaviour.

On a side note : people sometimes engage in destructive relationships. Again, there is no gain for the involved parts, but we are sometimes not very fast to realize this.

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  • $\begingroup$ A perfectly simple answer, but it fails to go into the depth that the accepted answer does. Although, your side note on people is quite interesting. It seems to have fueled the accepted answer considerably. $\endgroup$
    – blaizor
    Commented Jan 25, 2015 at 23:15
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So, the first thing I'd point out is that the only real reason to have any sort of relationship is for some kind of gain, whether it be for survival, emotions (like marriage), etc.

One-sided relationships happen in nature a lot (predation) because one species is strong enough to say "I want this and I shall have it" and the other can't do anything about it... besides run away. SOME creatures have produced relationships where both succeed in a symbiotic state. However, the opposite would have no rewards for either species and they'd both have an incentive to leave that environment.

The only place I can think to start looking would be an environment where a superior species purposefully or accidentally sets up an environment in which two lesser species are at odds with each other (like when two women are both really interested in the same man: their relationship is markedly non-symbiotic but neither wants to leave); I suspect an environment like this COULD occur in nature, but I don't know of anywhere it does.

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  • $\begingroup$ Your last example is more a competition for another ressource, which is frequent. In this case, the "winning" individual consider that the potential ressource is worth the conflict drawbacks. $\endgroup$
    – Uriel
    Commented Jan 25, 2015 at 19:54
  • $\begingroup$ But we can certainly find a lot of relationships (by no means limited to evolutionary ones) which offer a short-term benefit, but long-term harm. $\endgroup$
    – jamesqf
    Commented Jan 26, 2015 at 3:41
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A third entity is necessary to produce the illusion of a mutually harmful relationship. That entity must effect both parties negatively but through different mechanisms and the solution to each party's resulting malody must be provided by the other party.

At this point, their relationship appears to be mutually beneficial because each party helps the other to survive the effects of the third entity, but relationships are never so two dimensional. Each of the two original parties has a strong parasitic or amensalitic secondary relationship with the other which causes significant damage to the effected party but not as much as the third party would cause if not for the negating effect of the other.

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