Predation is a specific interaction between organisms in which the outcome is positive for one species and negative for the other. Predation can be thought of as consumer-resource exploitation, in which the predator feeds on the prey to gain a fitness benefit.
There are a multitude of different predators which can exist in a population:
- Carnivores: Kill and consume prey causing their removal from the population.
- Parasites: They consume a live host, but do not cause the hosts removal from the population.
- Parasitoid: They lay eggs on their host which eventually hatch and result in the consumption and removal of the host from the population.
- Herbivores: May act as predators, but are not as aggressive as carnivores. Generally, herbivores graze (i.e. cattle grazing vegetation).
- Cannibals: Are rare in wild populations and occur when the predator and prey are the same species.
Predation also has many influences on the structure of populations. For one, predators can allow for the coexistence of species. This is done by maintaining prey levels below carrying capacity and thus, the diversity of species can remain higher.
Additionally, predators can influence trophic cascades and cause a change in community structure. For example, pretend a trophic cascade consists of four species and they are ranked as follows:
Top Predator ---- Secondary Consumer ---- Primary Consumer ---- Basal Organism
If the top predator preys upon the secondary consumer, the next top species in the food chain, it will decrease in abundance, thus increasing the levels of the primary consumer in the food chain. The abundance of the primary consumer species increases because there are not many secondary consumer species around to prey upon them. Since the levels of the primary consumer will be high, this will suppress the levels of the most basal organisms of the cascade. Thus, two species will be of high abundance and two species will be of low abundance in this population.
Predation has a powerful influence on ecosystems and can strongly affect a population’s structure. However, predation is a natural process and is necessary in order to maintain balance within ecosystems.
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