19.3-19.4: Competition and predation

Intraspecific competition

Competition between individuals of the same species compete with one another for resources such as food, water, breeding, sizes etc.

What determines the population?

• Availability of such resources deterime the size of a population, the greater the availability the larger the population. Lower the availability the smaller the population.

Interspecific competition

• Interspecific competition occurs when individuals of different species compete for resources such as food, light, water etc.

Competitive exclusion principle

• When populations of two species are in competition one will normally have a competitive advantage over the other. The population of this species will gradually increase in size while the population of the other will diminish. If conditions remain the same, this will lead to the complete removal of one species. This is known as the competitive exclusion principle.

WHat does the competitive exlusion principle state?

• The principle states that where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other. In other words, no two species can occupy the same niche indefinitely when resources are limiting.

Predation

• Occurs when one organism is consumed by another.

Why does evidence collected on predator and prey population in a laboratory not reflective of what happens in the wild?

• Difficult to obtain data from natural populations since its not possible to count all the individuals in a natural populations.

• Its size can only be estimated from sampling and surveys

• These are only techniques we can use both do not guarantee complete accuracy

Effect of predator-prey relationship on population size

• Predators eat their prey, thereby reducing the population of prey

• With fewer prey available the predators are in greater competition with each other for the prey that are left

• The predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce

• With fewer predators left, fewer prey are eaten and so more survive and are able to reproduce

• The prey population therefore increases

• With more prey now available as food, the predator population in turn increases