I just watched a news show that had a segment on animals somehow reacting the the east coast earthquake before any humans could feel it, and a guy mentioned that the flamingoes somewhere clustered together, as they do when threatened by crocodiles or whatever. He said that was an evolved response, the idea being that you are less likely to be eaten if you are surrounded by your buddies.
I don’t see the logic in that, at least as regards evolution. I guess it makes sense for buffalo, since they can fight back, and standing in a circle with their butts inside and their horns outside would seem to be a good strategy.
But for flamingoes versus crocodiles, or sardines versus sharks, I don’t get it. It seems to me that it just makes it so the predators can’t miss, and that more of the prey would be easily eaten, which should not only hurt the prey as a species, but should increase the number of predators.
What’s more, if everybody scattered, the ones most likely to be eaten would be the weakest and/or slowest. Clustering together would make it more random, which would seem to lower the average quality of the survivors, thus weakening the species.
The logic would be that 1 of the flamingos would be eaten by a predator, but the chance of you being that one are lower, and gets even lower the bigger the flock gets.
Similarly, in WWII, ships in convoys were more likely to make it past German submarines than ships all alone. A few of the ships in the convoy might be sunk, but the rest made it safely. There were a few cases early on where the Convoy Commander made the error of telling all the ships to ‘scatter’ – the result of that was incredible carnage. (See PQ*17 for one example.)
P.S. I think you have herd idea backwards.
Horses, mules, etc. threatened by a predator get in a circle with their heads inward, and their hind ends outward – because their most potent defensive weapon is a crippling kick from their powerful hind legs. I haven’ ever raised buffalo, but I think they would use the same defensive strategy.
I appreciate the response, but it’s not clear to me that your counterexamples are relevant. If the convoy comprises nothing but unarmed cargo ships, then I don’t understand why staying together helps them, but I thought most convoys had armed escorts, and in that case the strategy makes perfect sense. My main question was about animals that are essentially defenseless.
As for the side issue about animals who are not defenseless, I’m even more sure that your horses and mules don’t contradict what I said. If a horse’s best defense is to kick, then of course (of course) it would have its head inward. But I don’t see why that should apply to buffalo.
Obviously it depends on the animal. The great apes climbed a tree, which makes good sense because that’s an advantage they have. An advantage a flamingo has is that it’s damned hard to pick out a specific flamingo, which means the predator will probably get some other pink leggy chump, not you!
I see that, but isn’t evolution more about the species than the individual? Look at ants and bees; clearly the individuals are sacrificed for the good of the hive or colony. Grouping together makes sense for a species when it fights back, but not when it just sits there waiting to be eaten.
That explains why a lower proportion of the population will get eaten if there are more members of that population, but it does not make it clear (to me, at any rate) why it is better for defenseless prey animals to gather together in a tight bunch.
As for WWII convoys, I thought the method was not just to send merchant ships out in bunches, but to send a warship or two along with them for protection. As a warship can defend several merchantmen almost as well as it can defend one, it made sense to send the merchantmen in bunches. (Scattering, of course, would mean that most of the ships would become separated from their protectors, and thus become vulnerable, as you say.)
Maybe it is true that even unescorted convoys are safer than the same number of merchant ships sailing separately, and I am certainly willing to believe that prey animals are safer if they gather together, but I do not think you have explained why, and that was the question.
In many cases predators single out an individual who has strayed from the pack, is too slow to keep up with them, lost or weakened, etc. Nobody wants to be that guy. They try to blend in with the crowd where they have better odds as individuals, not a species.
That individual drive for survival is still beneficial to the species as a whole even if it’s inevitable some of them are going to wind up dinner to the predators. It enforces the ‘survival of the fittest’ concept in many cases as the one who isn’t in the pack is somehow weakened.
My hazy understanding of the “safety in numbers” defense strategy is that a lot of predators are accustomed to focusing on a specific target animal when making the fatal strike, and large crowds – especially large moving intermingling crowds – literally present too many choices. The predator shifts focus rapidly between the moving prey individuals and has a hard time choosing one and making the fatal strike.
My somewhat clearer understanding of the reason WWII convoys were effective is that there were two different distinct advantages to convoys:
In the ocean, even a large convoy occupied a tiny space. The biggest difficulty submarines had (especially before radar) was finding the ships, not sinking them. Ships in convoy were not appreciably easier to spot than individually-sailing ships, but they came along a lot less frequently. Individual ships offered many separate opportunities to spot a target. In fact, postwar statistical analysis shows that the vast majority of sinkings were ships sailing alone.
Similarly, submarine-hunting warships’ main difficulty was finding the submarines. They tried patrolling in “sweeps” to find subs, but the subs generally saw them coming and submerged. Convoy escort duty, on the other hand, drew the submarines in, and they would inevitably reveal themselves, and could subsequently be attacked. In this sense, convoy was an offensive scheme, surprisingly – the only one that would reliably bring warships to bear against the submarines and allow them to try and win the battle by sinking them.
You seem to be under the impression that flamingos can’t fight. I question this: Just about every animal can fight, and will if necessary. Now, a lone flamingo versus a croc, the bird’s not going to be able to put up enough of a fight to make a difference. But a whole flock of them considerably increases the odds that one of them will be able to peck out one of the croc’s eyes or something.
I’m not a professional biologist, but maybe you’ll take these answers:
The big advantage of a flock or herd (and maybe school as well) is that there are lots of lookouts. Think of every scene of hunting lions: the beginning is always the lions sneaking up on the prey (or setting an ambush or something). With a herd, it’s a lot harder for the lion to surprise the prey because there’s always someone looking in their direction. Plus, by sharing lookout duties, the prey get to spend less time looking and more time eating, which is a big thing for grazers that need to eat a lot. Particularly in the flamingo case, it might be worth remembering that a flamingo doesn’t need to fight off a crocodile, at least until the crocodile gets a jetpack or surface to air missile. The flamingo just needs to know where the crocodile is so it can take off when the croc gets too close. With a group of flamingos, they can keep watch in every direction, while still spending most of their time feeding.
I think I vaguely remember some evidence that groups of animals can confuse predators, but I doubt this is a major factor: it’s far too easy for predators to evolve towards being able to deal with multiple targets.
Some animals like buffalo probably gain by being able to defend in a group. That’s not true of gazelles or whatever, so clearly defense isn’t the biggest reason for herding.
Finally, evolution doesn’t particularly care about the good of a species. Cooperation only evolves when it benefits the individual (or its close family, which explains some of the social insect phenomenon). But it still can make sense to group together. For instance, if a bunch of us need to get past a predator, and it can easily kill all of us if we go one by one, but will be overwhelmed and only be able to kill some of us if we rush past in a group, cooperation makes sense from an individual (and therefore evolutionary) standpoint. It’s not that I’m sacrificing myself for all of you guys; it’s just that my chances are a lot better of not being the sacrifice than they would be if I tried to go it alone. However, I don’t think this is the dynamic in place in herding; if lions start catching more gazelles than they can eat, they’ll have more kids and the population will grow until they’re getting just enough food. Now this is the dynamic in place in many insect swarms (seven-year ‘locusts’/cicadas, mass mayfly hatchings, etc.). The key is that the insects only emerge for a short time, so predators’ populations can’t build up.
Back to the OP, one of the things being ignored so far is that predators are relatively few in number. And they’re not simple killing machines. Having killed one prey, they usually take time to eat, and may have no interest in eating again for hours.
If a small flock of flamingoes landed in a large school of sharks, huddling close together would indeed produce a feeding frenzy and near total destruction for the flamingoes.
But that’s not the real world situation. It’s more like this:
There is a few acres of marshland, one croc, and 100 flamingoes. If they spread out, somebody is going to be surprised and eaten. Then the croc will swim away satisfied. Or he’ll try to sneak up on another clueless bird.
If they cluster together, probably somebody will see the approaching croc and sound the alarm & all will fly away. If no alarm is raised, somebody will be eaten. Which will happen close enough to the others that the alarm is raised and again the rest fly away safely.
In the scattered situation, any one flamingoe’s odds on being the unlucky lunch are 1/flock count.
In the bunched situation, your odds are essentially number in 1/*flock perimiter count *if you are a perimeter bird & zero if you’re a flock interior bird. As the flock grows, the interior count grows more rapidly than the perimeter count. Which is why a flock of 5 is little better than separated individuals, but a flock of 100 or 500 confers a big net benefit.
The game changes completely if you assume a “flock” of predators as well. But again that’s not the real world situation in most cases.
I think he is referring to the fact that evolution doesn’t really “care” about the survival of the species. All that is preferred is genetic mutations that increase the likelihood of the survival of the gene itself. This distinction is explained in detail in Dawkins book “The Selfish Gene”, among others I’m sure.
Applying this logic to the “herd mentality” gene, and its pretty easy to see why this would be preferred to a “fly solo” gene - the odds of the mutation surviving in a host that is not very strong individually is much higher in the “herding” case.
To add a bit to my above response, consider the two “steady-states”: Herd Together and Spread Apart. If we are talking about an organism with very little chance of surviving a predation attempt (like, say, a flamingo), then we can evaluate these two steady-state survival rates.
In fact, if we take as a given that any predation attempt on a flamingo flock will succeed (not a great approximation, but failed attempts don’t change things very much), then these two steady-states have the same survival rates. For a flock of 100, each individual has a 1% chance of survival whether the flock herds together or spreads apart.
However, imagine throwing a mutation into each of these states which runs counter to the flock behavior.
Into the Herd Together flock an individual mutates to prefer running off by itself. It now has something much closer to a 50% survival rate (either the predator attacks the rest of the flock and kills one of them or it attacks and kills the loner). This mutation will clearly not be selected for in this population, since it has a much lower survival rate than the individuals without it.
Into the Spread Apart flock an individual mutates to prefer herding with another individual. Its surival rate is now roughly 0.5% (the ~1% chance that the predator attacks his twosome times the 50% chance that it eats him instead of his buddy). This mutation will be selected for, as it cut the individual’s death-rate at each predation event in half.
This shows that even though two behaviors may be equivalent when analyzed independently, mutations injected into them can be stable or unstable. In fact, even if the Spread Apart behavior had a higher average survival rate than Herd Together, its possible that a rogue actor herding might be higher still, and thus be selected for. What’s good for the species isn’t necessarily what’s good for the gene (and its individual host). That is, the stable steady-state might in fact be “worse” on average for the species than the unstable steady-state, and still be the result achieved by natural selection. This is also discussed at some length in the Dawkins book, IIRC.
This doesn’t work. Any given bird’s total chance of being selected is still 1/flock count, once you consider the chance of being a perimeter bird and the chance of any given perimeter bird being selected.