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I'm trying to chart the roadmap of the evolution of a variety of fictional amphibian creatures which hunts in pairs. But, I don't know of many inspirations in nature where animals hunt in pairs.

What history/evolution/environment would incentivize through conscious thought or instinctively of selective pressure of a mid-tropic-level species to hunt in pairs?

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Hunting in group gives the obvious advantage of the number, but there is no hard limit to stop it at just two, because the more the better.

The only stop to the size of the hunting pack is the size of the prey: you can't feed 100 hunters with a single sparrow.

Therefore the only plausible way to favor pair hunting is to have preys big enough to feed a couple, which would probably be a male and a female, and not more.

Or you could have the pair be composed by two different species in a sort of mutualistic relationship, like the notorious case of the African bird which helps honey seekers in finding beehives in exchange of a share on the hunt: the bird has a better way of finding the beehive, while the human has more ease of cracking it open.

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  • $\begingroup$ Possible dynamical constraints of predator-prey interactions are one type of pressure, but for the success and reputation of this site, I'm wondering if there's more depth. For instance, it could be related to finding and maintaining a mate or "family" of some kind too, or something about the complexity of hunting tactics. $\endgroup$
    – StackQuest
    Apr 19, 2022 at 17:53
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    $\begingroup$ +1 for prey size.. answer is there, mine is not needed. $\endgroup$
    – Goodies
    Apr 19, 2022 at 20:01
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    $\begingroup$ +1 for "the more the better" - if the prey requires 2+ hunters and there are only 2 then as soon as one is injured, lame or sick then neither eats and both die. Better to have a larger group which can continue after taking a loss (and possibly give the injured hunter time to recover) than for one misstep to doom both. $\endgroup$ Apr 20, 2022 at 7:01
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Brothers.

cheetah bros

source

Cheetah brothers stick together and hunt as a pair or trio. It makes sense for brothers to cooperate. They share genetic material and so cooperation produces a fitness benefit for their shared genes. In an area with a diversity of prey sizes, teaming up with a brother allows them to take down large prey out of reach for a single animal such that cooperation does not mean less meat to go around. This also decreases food competition with the local females and cubs which are probably related to the brothers.

In a species where males are uninvolved with rearing young, a noncompetitive brother unit might both mate with the same female. The resulting cubs are from one of them, or maybe both; all ok from an evolutionary perspective.

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Dichotomy:

Any time you might have specialization of function, having a representative of each kind would be a distinct advantage.

Imagine, if you will, a species where the male is strong and has great endurance, while the female is quick and has a preponderance of fast-twitch muscles and explosive outbursts of activity (or vice versa). The slower, stronger member can stalk (possibly even carrying the quick one), then when the prey is in range, the quick individual sprints to the prey and goes in for the kill.

The strong one can protect and care for the quick one in the event of an injury, and the strong one can butcher the animal or carry it back to the den/home. But the strong one is too slow to catch the prey, while the quick one has too little endurance to stalk.

  • This dichotomy could also be a generational factor as well. Adults/elders are slower but have grown large and strong. Older individuals may be skilled trackers and observers, and they advise or train the younger, quicker members. So prey requiring both quick reactions AND a lifetime of experience would need pairs like this.

Pairing minimizes the number of individuals needed to be fed. This could be a mated pair OR a parent and child.

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Breeding Pairs

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Many animals form pairs to raise their young. It requires no leap of imagination to have animals that stay in pairs the rest of the year. This includes hunting together. Easy.

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    $\begingroup$ Side note: actually very uncommon in birds (and dino's) to hunt together. The Aplamado falcon known for hunting in pairs, and deserves a mension, as well as Harrises' Hawks that hunt in flocks. $\endgroup$
    – Goodies
    Apr 19, 2022 at 19:57
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    $\begingroup$ @Goodies In today's day and age it is practically unheard of for dinosaurs to hunt in pairs. $\endgroup$
    – Daron
    Apr 19, 2022 at 20:05
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    $\begingroup$ @Daron—Even so, Goodies gave a great example of a present-day dinosaur that does hunt in pairs. $\endgroup$
    – Vectornaut
    Apr 20, 2022 at 8:11
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For more about co-operative strategies like this, google 'evolutionarily stable strategies' or ESS. There are many like the cheetah brothers where evolution prefers (even slightly) co-operation that might otherwise seem lacking in benefits. And usually these strategies are not easily replaced by others.

https://en.wikipedia.org/wiki/Evolutionarily_stable_strategy

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I think you could cause a limit in the hunting group by having a predator in the environment. This may not cause a hard limit but would be like a soft limit if the predator is large and undefeatable in numbers.

It needs to be large enough that it won't care about single or pairs of your creatures but if there's any more then it considers it worth it's time to hunt them down.

And obviously it must be undefeatable by your creatures so that they don't just form very large hunting parties to hunt it. There's a number of ways to do this depending on how you want to and the characteristics of your creatures.

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A pair of amphibians could work together to enable some relatively unique hunting tactics. One member of the pair could lie just above the waterline, feigning distress and looking like a fish out of water. When something approaches what they think is an easy meal, the second creature would ambush it from under the water. A large hunting group wouldn't be as effective because it's too hard to hide a large number of creatures in the same shallow water.

Alternatively, your creatures could lure their prey into the open by mimicking their prey's call. The amphibians have relatively simple vocal tracts, and it takes two of them "singing" together to produce something that sounds reasonably like the complex mating call that they're impersonating. They're not smart enough to coordinate an entire amphibian choir, so three or more would produce a cacophony that doesn't sound like anything in particular.

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Twin attunement

A completely endogenous solution.
Your species is quite intelligent, but their brain development is genetically and developmentally much more variable than ours - they have effective forms of communication, but understanding each other and accurately predicting each other’s actions is more difficult, similar to the barriers between, say, autistic and neurotypical humans.

There is only one other individual who shares the exact same genetics and developmental environment as you: your identical twin. Their brain is an almost exact mirror copy of yours. You catch your twin’s meaning effortlessly, you can tell what they would do in a given situation with uncanny precision. Your mirror neurons play a strikingly accurate replica of your twin’s behaviour even when you can’t actually see them. As you can imagine, hunting together is beautifully coordinated and reliably deadly.

The species births monozygotic twins almost exclusively; single births are abandoned by their mothers, and triplets are culled to two. Those who lose their twin later in life tend to die soon after, although myths abound of hardened hermits fending for themselves in desperate solitude.

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