BBC - GCSE Bitesize: Predators and their prey
Trophic Links: Predation and Parasitism. We wish to learn: how predators affect prey populations, and vice-versa; what stabilizes predator-prey interactions and. The prey is the organism which the predator eats. Some examples of predator and prey are lion and zebra, bear and fish, and fox and rabbit. The words. Predators eat prey and maintain the health of the prey populations. The predators eat the old, sick, weak and injured in prey populations. As the population of the.How to Make a Predator Prey Graph
Logic and mathematical theory suggest that when prey are numerous their predators increase in numbers, reducing the prey population, which in turn causes predator number to decline. The prey population eventually recovers, starting a new cycle.
T Paramecium, which also proved useful in test-tube studies of competition, was placed in culture with a predaceous protozoan. These laboratory studies found that cycles were short-lived, and the system soon collapsed. However, if one added more paramecium every few days, the expected cycle was observed.
These results suggested that the predator-prey system was inherently self-annihilating without some outside immigration. The question then arose: Observing that frequent additions of paramecium produced predator-prey cycles in a test-tube led to the idea that in a physically heterogeneous world, there would always be some pockets of prey that predators happened not to find and eliminate.
Perhaps when the predator population declined, having largely run out of prey, these remaining few could set off a prey rebound. Spatial heterogeneity in the environment might have a stabilizing effect. A laboratory experiment using a complex laboratory system supports this explanation. A predaceous mite feeds on an herbivorous mite, which feeds on oranges. A complex laboratory system completed four classic cycles, before collapsing.
Observations of prickly pear cactus and the cactus moth in Australia support this lab experiment. This South American cactus became a widespread nuisance in Australia, making large areas of farmland unusable. When the moth, which feeds on this cactus, was introduced, it rapidly brought the cactus under control. Some years later both moth and cactus were rare, and it is unlikely that the casual observer would ever think that the moth had accomplished this.
Once the cactus became sufficiently rare, the moths were also rare, and unable to find and eliminate every last plant. Inadequate dispersal is perhaps the only factor that keeps the cactus moth from completely exterminating its principal food source, the prickly pear cactus. Prey defenses can be a stabilizing factor in predator-prey interactions.
Predation can be a strong agent of natural selection. Easily captured prey are eliminated, and prey with effective defenses that are inherited rapidly dominate the population. Examples include camouflage in the peppered moth, and prey that are nocturnal to escape detection. Bats capture moths in flight, using sonar to detect them; some moths are able to detect incoming sonar, and take evasive action.
Perhaps seriously unbalanced system simply disappear, and those that persist are ones in which the predator is not "too effective", likely because the prey has adaptations to reduce its vulnerability.
Note that the prey population size is on the left vertical axis and the predator population is on the right vertical axis, and that the scales of the two are different after Huffaker, [fig.
It is apparent from the graph that both populations showed cyclical behavior, and that the predator population generally tracked the peaks in the prey population. However, there is some information about this experiment that we need to consider before concluding that the experimental results truly support the predictions made by the Lotka-Volterra model.
To achieve the results graphed here, Huffaker added considerable complexity to the environment. Food resources for E. Additionally, the oranges were partially isolated with vaseline barriers, but the prey's ability to disperse was facilitated by the presence of upright sticks from which they could ride air currents to other parts of the environment.
In other words, predator and prey were not encountering one another randomly in the environment see assumption 4 from the Introduction.
Predator -prey relationship
A good model must be simple enough to be mathematically tractable, but complex enough to represent a system realistically. Realism is often sacrificed for simplicity, and one of the shortcomings of the Lotka-Volterra model is its reliance on unrealistic assumptions.
For example, prey populations are limited by food resources and not just by predation, and no predator can consume infinite quantities of prey.
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.