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Predator-prey cycles

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What effect do interactions between species have on the sizes of the populations involved? Learn about the dynamics of predator and prey populations, and how they can influence one another’s patterns of growth and decline. 

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  • duskpin ultimate style avatar for user Sriabhi Venkat
    will there be any point in time where predators are the same as prey? If so, what is that called?
    (5 votes)
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    • blobby green style avatar for user pstirling
      I wondered this too, but it would depend on the relative sizes of the predator and prey. Eg a wolf needs to eat a lot of mice, so a "low" population of mice would still be much higher than the wolf population. The lynx and hares in the video would be more equal, but one lynx still eats many hares over its lifetime. Plus of course lynx eat more than hares and hares have other predators.
      (1 vote)
  • duskpin ultimate style avatar for user ltlilli353
    can the predator and prey population be the same?
    (2 votes)
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  • area 52 blue style avatar for user amoungus_likes_cheese1874
    I just had a thought, has a ever prey been able eat the predator of that species?
    (2 votes)
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    • male robot donald style avatar for user Tybalt
      As crazy as it may sound at first, yes! These interactions are called "Predator-Prey Reversal", which can occur because of multiple factors, like prey size.

      For instance, the larvae of Epomis, a genus of ground beetle, are preyed upon by frogs. However, once a frog catches a larva, the larva will promptly attach to the frog and slowly consume it.
      (1 vote)
  • piceratops seed style avatar for user nicolas.weber
    what would happen if two predators meet
    would the compete for food
    (2 votes)
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    • aqualine ultimate style avatar for user jtbabione
      I'd say it depends. If there isn't any other prey besides what the first predator is hunting, then they would have to compete for food. But if there is other prey that the second predator prefers, the second predator would go after that instead of competing for the prey that the first predator prefers. And then if one of the prey somehow ends up leaving completely and the predator that hunted that prey wanted to stay, both of the predators would have to compete again depending on how much prey there is and the variety of prey. Like I said, I'd say it depends on the situation
      (0 votes)
  • purple pi teal style avatar for user Evie
    What are these relationships called?
    (0 votes)
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    • blobby green style avatar for user rivera0000g
      Go to differential equations and find Lotka - Volterra predator prey model (can use it in producer/consumer relations too). Kolmogorov generalized this model. For a man with a manifold everything is a dynamical system... that is, we, as far as I know, haven't got a better model of reality, than a dynamical system. There is a lot of progress in the field, but no breakthrough. This should be a side-kick from dynamical systems, rather than an article about ecology, I guess.
      (1 vote)
  • starky tree style avatar for user Alexander
    What would happen if both the predator and prey populations are equal?
    (1 vote)
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  • blobby green style avatar for user Za'mirea
    Why would we want to have a big capacity?
    (1 vote)
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  • starky sapling style avatar for user morgan.walker
    Is there a possibility that when predators become more than prey, can the prey still prosper under those conditions?
    (1 vote)
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  • blobby green style avatar for user Alberto Hurtado
    Does everything have a niche
    (0 votes)
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    • duskpin ultimate style avatar for user Amir T
      All organisms are dependent on having a niche. Every organism lives in a specific habitat and because of competition between species and within, they need to develop a way of living to avoid competition. Avoiding competition is important because two species can't occupy two identical realized nische, otherwise the most effective species of them would outcompete the other. So a niche is a way of living and under which circumstances an individual lives under. Without a niche, it would become hard surviving.
      (2 votes)
  • starky sapling style avatar for user Xaviour Hernandez
    At in the video, Sal accidentally uses pink for gray and covers it up.
    (0 votes)
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Video transcript

- [Voiceover] What I wanna do in this video is think about how different populations that share the same ecosystem can interact with each other and actually provide a feedback loop on each other. And there's many cases of this, but the most cited general example is the case when one population wants to eat another population. And so you have the predator population that likes to eat the prey. So you have the predator and prey interactions. I'm doing the prey in I guess a somewhat bloody color, I guess 'cause, well, they're going to be eaten. So let's just think about how these populations could interact. Let me draw a little chart here that you're probably familiar with by now where we show how a population can change over time. So the time, the horizontal axis is time. The vertical axis is population. Population. And so let's just, in our starting point, let's say that our prey is starting out at a relatively high point. Let's say we're right there in time, and let's say for whatever reason, our predator population is relatively low. So what do we think is going to happen here? Well, at this point, with a low density of predators, it's gonna be much easier for them for find a meal, and it's gonna be much easier for the prey to get caught. So since it's more easy, it's easier for the predators to find a meal, you can imagine their population starting to increase. But what's going to happen is their population is increasing. Well, it's gonna be more likely that they're gonna, they prey is gonna get caught. There's gonna be more of their hunters around, more of their predators around. So that population is going to start decreasing all the way to a point where if the population of the prey gets low enough, the predators are gonna have, they're gonna start having trouble finding food again, and so that their population might start to decrease, and as their population decreases, what's gonna happen to the prey? Well, then, there's gonna be less predators around, so they might be able to, their population might start to increase. And so I think you see what's happening. The predator and prey, they can kind of form this cyclic interaction with each other. And what I've just drawn, this is often known as the predator-prey cycle. And I just reasoned through that you can imagine a world where you can have the cycle between predator and prey populations. But you can also run computer simulations that will show this, and even observational data out in the field also shows this. One of the often cited examples is interactions between, between the snowshoe hare, which would be the prey in this situation, and the Canadian lynx, which would be the predator, the predator in this situation. And you see a very similar cycle to what I just drew, kind of just reasoning through it, and this, right here, is actual data. You see the passage of time here, and this is a long passage of time. We're starting in the early 1800's going all the way to the early-mid 1900's. So it's roughly 100 years of data that we're showing, and in the vertical axis, you have thousands of animals and we're plotting both the population of snowshoe hares and Canadian lynx in a certain area on this chart. And as you see, when the prey population is high, when the prey population, sorry, when the predator population is high, when we have a lot of the Canadian lynx around, that we see a lower, a lower population of the prey, of the hare. But then as, since you have a low population of the food in this situation, the predator population starts to decrease. So let me draw an arrow here. The predator population starts to decrease and, let me do that same blue color. And so the predator population decreases, and as that predator population decreases, well then the prey population increases 'cause there's less folks around to hunt them. So the prey population increases, and you see that the other way around. When the prey population is really is, well maybe we'll show it right over here, and this is real data. That's why it's not always super clean. But when the prey population is really, really high and the predator population is relatively low, well, then, the predators say, "Hey, it's really "easy for us to find meals right now." That's kind of that starting point in that, when I was just reasoning through it. And so their population starts to. Oh, oops, what did I do? There, there. Let me make sure. So their population starts to increase, and as the predator population increases, well the prey population, the prey population is going to decrease. So this is real data showing the snowshoe hare, the prey, and the Canadian lynx, the predator, on over many, many decades to show this predator-prey cycle.