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Examples of prey predator interactions where density of predator is very low (has a threat of extinction) and prey form groups when the predator attacks the prey for food.

I have searched this in net but not get examples. Please help me to supply some examples with a brief interaction of type discussed above.

EDIT

Specialty of predator:

Predator population has a threat of extinction due to their low population. They have the difficulties in locating acceptable mating partners for sexual reproduction during their receptive period due to low population densities.

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    $\begingroup$ This sounds like a homework question. Look up bait fish ball. Use what you learn there to guide other searches. $\endgroup$ – akaDrHouse Nov 4 '15 at 18:01
  • $\begingroup$ @akaDrHouse Thanks. In that case which one is the engendered predator mostly feeds on the bait fish. Please provide me more such examples of prey and predator pairs having such interaction. $\endgroup$ – user1942348 Nov 4 '15 at 18:45
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    $\begingroup$ Homework questions are off-topic on Biology.SE. $\endgroup$ – Remi.b Nov 4 '15 at 21:51
  • $\begingroup$ This post might help you to understand how prey-predator interactions affect population size. The post does not contain examples though as it focuses on the theoretical aspect. $\endgroup$ – Remi.b Nov 4 '15 at 21:52
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    $\begingroup$ Are you asking for cases where the flocking behaviour is used specifically against low-density predators, or flocking against predators in general? At the moment, it's unclear why are asking specifically about low-density predators,and bring the risk of extinction of the predator into the equation. $\endgroup$ – fileunderwater Nov 5 '15 at 8:33
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  1. A low predator density is not synonym with "threat of extinction". Of course large predators are more prone to extinction because of lower numbers, but they usually exist in lower densities than prey (look, for instance, Lotka-Volterra equations and graphics, and also biomass and food pyramids). The risk of extinction is usually caused by fragmentation of habitat, that reduces population and gene flow.

  2. Many preys form groups to avoid predation. That happens with schools of fish, caterpillars that walk as a multi-organism mass, grasshoppers that change behavior into locusts, bovids and related mammals, that make a circle with the horns to the outside to defend against predators.

  3. So, it's not clear what you're asking. Is there any special case of low density of predator/modified prey behavior?

EDIT: If you want a more concrete answer, it will depend of the geographic region. But everywhere the largest predators are usually the most endangered. They usually prey on large mammals (but not only, since a jaguar can eat an anaconda or an alligator, etc.).

Here is an example from Alaska:

http://www.nps.gov/gaar/learn/nature/muskox-circle-defense.htm

If there is one predator—a lone wolf for example—the defense strategy is to form a line. If a wolf pack surrounds the group, the muskoxen will form a tight circle, all facing outward, forming a phalanx of heads and horns.

https://www.youtube.com/watch?v=pb6Rke7jiTc

http://www.iucnredlist.org/details/3746/0

Although IUCN has no data about the subspecies Canis lupus arctos, they say:

Originally, the Grey Wolf [Canis lupus] was the world's most widely distributed mammal. It has become extinct in much of Western Europe, in Mexico and much of the USA, and their present distribution is more restricted; wolves occur primarily but not exclusively in wilderness and remote areas. Their original worldwide range has been reduced by about one-third by deliberate persecution due to depredation on livestock and fear of attacks on humans.

It may not be the case in Alaska, though.

Another example from Africa are zebras. There are many species from two different subgenera, but if Equus zebra is endangered, what we may think about their predators! Lions, for instance. They flock in groups so the stripes may confuse the predators about where one individual ends and the next begins - making a successful attack more difficult.

http://animals.howstuffworks.com/mammals/zebra-stripes.htm/printable

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  • $\begingroup$ "Is there any special case of low density of predator" - Answer is yes. Special case is predator population has a threat of extinction due to their low population. They have the difficulties in locating acceptable mating partners for sexual reproduction during their receptive period due to low population densities. $\endgroup$ – user1942348 Nov 7 '15 at 4:12
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    $\begingroup$ Not sure if its a "special case" or just a usual low-density predator worsened by other causes of extinction, such as deforestation. Still, not clear what the question is. $\endgroup$ – Rodrigo Nov 7 '15 at 5:11
  • $\begingroup$ Ok. It may be just a usual low-density predator worsened by other causes of extinction, such as deforestation. Only thing is that predator should have threat of extinction. $\endgroup$ – user1942348 Nov 7 '15 at 5:16
  • $\begingroup$ May I get more concrete answer that I need? $\endgroup$ – user1942348 Nov 10 '15 at 6:29
  • $\begingroup$ In any example given you can add a theoretical extinction risk. That's very common nowadays. You can look at iucnredlist.org, for instance. $\endgroup$ – Rodrigo Nov 10 '15 at 9:49
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Many species of animals use flocking/ schooling/ shoaling/ etc as a mechanism to confuse predators. A few examples are tuna, starlings, goldband fusiliers. tuna and goldband fusiliers use their reflective scales to blind and confuse the predator, whereas starlings use sheer numbers to overpower and throw off their predator. The large groups tend to scare away far away predators.

The act of grouping is not dependent on whether or not the predator is endangered or not, but there would be cases where both the predator is endangered and the prey uses grouping. For example, several species of owl are endangered, which prey on starlings.

https://en.wikipedia.org/wiki/Collective_animal_behavior#Protection_from_predators

http://www.fcps.edu/islandcreekes/ecology/european_starling.htm

http://rsif.royalsocietypublishing.org/content/10/85/20130305

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