Competition and Predation

In an ecosystem, competition arises when resources are in limited supply and organisms strive to obtain these resources. Predation describes a specific type of competition in which a predator consumes its prey. Both of these factors are examples of biotic factors that influence the size of a population.

What are the types of competition?

There are two types of competition in biology:

• Intraspecific competition
• Interspecific competition

What is intraspecific competition?

When competition arises between two members of the same species, it is known as intraspecific competition. The availability of resources in the habitat determines its carrying capacity, which determines the population’s size.

• When resources are more abundant, or there are fewer individuals in the population, there is less competition.
• There is more competition when there are fewer resources or when the population is approaching its carrying capacity.

This phenomenon is visualised in the following graph.

Fig. 1 - Population size and carrying capacity

Different resources are intrinsically linked to one another, which leads to interesting effects on competition.

What is interspecific competition?

When competition for resources arises between individuals of different species, it is known as interspecific competition. No two species can occupy the same niche in the same habitat; if one species has even a slight advantage over the other, it will outcompete the other to the point of extinction. This concept is known as the competitive exclusion principle.

The competitive exclusion principle

The competitive exclusion principle states that two species that use the same limited resource cannot co-exist at constant population levels; the one that uses these resources most effectively will eliminate the other.

Investigating the effects of competition on population size

In theory, we can expect competition to significantly affect the size of a population. However, in practice, it can be quite challenging to prove because many complex and interconnected factors can affect the size of a population.

For instance, abiotic changes in the environment can interact with or mask the effects of biotic factors. Competition can also take some time to affect the population, which means it can be hard to spot and easy to misattribute to something else. Finally, it is often harder to establish causal links in natural populations, particularly when studying rare or protected species. Researchers often have to rely on incomplete, correlational data, which might not accurately reflect what is happening in the population.

What is predation?

Predation is a process wherein one organism consumes another organism. The predator is the organism that feeds, and the prey is the organism being consumed.

Predators and prey often have closely linked evolutionary relationships because to survive, predators must evolve adaptations that allow them to catch their prey better. In contrast, prey must evolve adaptations that will enable them to escape their predators better.

There are many examples of predator-prey relationships in nature.

Five types of predation

• Parasitism - when one organism harms another organism by obtaining food from it.
• Commensalism. When an organism gains benefit from another organism, which is not benefited nor harmed.
• Mutualism. When both organisms benefit from the relationship.
• Competence. When two living organisms require the same resources. They become competitors and harm each other.
• Cooperation. When both species benefit from the relationship, however, their existence does not depend on each other.

What is the effect of the predator-prey relationship on population size?

The relationship between predators and their prey has a cyclical effect on population size. Imagine a population of owls that feed on a population of mice.

1. The owls eat the mice, which reduces the mice population.
2. With fewer mice available, intraspecific competition between the owls increases; eventually, the owl population also declines as some cannot catch enough mice to survive and reproduce.
3. As a result of a reduced predator population, more mice survive and reproduce. The mice population increases again.
4. The increase in the mice population replenishes the food supply for the owls, which can again recuperate their numbers and begin the cycle anew.

Why aren’t the prey exterminated by the predator?

In laboratory experiments, predators can often exterminate the prey population very quickly. However, in natural settings, this rarely happens. There is a wide range of external factors in the wild that can allow the prey to survive. For instance, the area over which the prey population can disperse is usually much larger and more varied; this makes them harder to find and harder to catch. Predators may also have to contend with other factors such as competition with other potential predators, surviving the effects of heat or cold, and navigating difficult terrain, or they might even have to survive as prey themselves.