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Main content
Current time:0:00Total duration:5:09
AP.BIO:
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Video transcript

what I want to 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 a predator and prey interactions and doing the prey and I guess it's somewhat bloody color I guess because 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 the how 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 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 going to be much easier for them to find a meal and it's going to be much easier for the prey to get caught so since it's more easy it's it's easier for the Predators to find a meal you could imagine their population starting to increase but what's going to happen is their population is increasing well it's going to be more likely that they're going to the prey is going to get caught there's going to be more of their hunters around more of the Predators around so that population is going to start decreasing all the way to a point where the population of the prey gets low enough the Predators are going to have they're going to start having trouble finding food again and so that their population might start to decrease and as their population decreases what's going to happen to the prey well then there's going to 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 side of 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 could imagine a world where you could 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 one at 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 1800s going all the way to the early mid 1900s so it's roughly a hundred 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 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 that 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 so the predator population decreases and as that predator population decreases well then the prey population increases because there's less there's less folks around to hunt to 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 so 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 it's really easy for us to find meals right now that was kind of that starting point in that and when I just was reasoning through it and so their population starts stow ups what did I do and they're 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 at the prey and the Canadian lynx the predator on over over many many decades to show this predator prey cycle
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