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Science

Populations and pyramids

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Predator and prey populations

All living things within an ecosystemecosystem: A community of animals, plants and microorganisms, together with the habitat where they live. are interdependent. A change in the size of one population affects all other organisms within the ecosystem. This is shown particularly clearly by the relationship between predatorpredator: An animal that hunts, kills and eats other animals for food. and preyprey: organisms that predators kill for food populations.

There is a continuous tussle between predators and their prey. Predator speciesspecies: Used in the classification of living organisms, referring to related organisms capable of interbreeding. need to be adapted for efficient hunting if they are to catch enough food to survive. Prey species, on the other hand, must be well adapted to escape their predators, if enough of them are to survive for the species to continue.

If the prey populationpopulation: A group of members of a single species living in a habitat. in an ecosystem grows, predator numbers will respond to the increased food supply by increasing as well. Growing predator numbers will eventually reduce the food supply to the point where it can no longer sustain the predator population ... and so on.

Case study 1: Ladybirds and aphids

The animation shows this predator/prey dynamic between a population of ladybirds (predators) and a population of aphids (their prey). The graph showing the relationship between them will look fairly similar for any two populations of predators and prey.

Case study 2: the Canadian lynx and snowshoe hare

Another example of the predator/prey dynamic is the rise and fall in numbers of Canadian lynx and its favourite prey the snowshoe hare. The two populations were estimated each year for some 75 years from the number of animals caught by fur traders. The hare population was found to rise and fall in a ten-year cycle, with that of the lynx following two years later. No other cat is so dependent on a single prey species, which is why there is such a clear pattern of interdependence between the two populations.

between 1845 and 1925 the number of each animal has varied between less than 10,000 and up to 140,000

The predator/prey dynamic between canadian lynx and snowshoe hare populations

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