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.
Biotic factor: refers to a living component of an ecosystem.
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
Intraspecific competition: when competition arises between two members of the same species.
Carrying capacity: the maximum population size of a species that can be sustained by its specific environment, given the resources available.
Different resources are intrinsically linked to one another, which leads to interesting effects on competition.
Imagine a population of apes that compete with one another for territory, which provides them and their families with food and attracts new mates. A given habitat will have a limited amount of space, and the exact size of the territory will grow or shrink depending on the inhabitants’ need for resources.
Suppose that the number of individuals in the population remains constant. In times of plenty, a territory can be relatively small, which means an area can house more territories. There would therefore be less competition among the males. However, when food is scarce, a territory would have to cover more ground to be viable. This occurrence lessens the number of territories available in an area and increases the amount of competition between the males.
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.
Interspecific competition: when competition for resources arises between individuals of different species.
Competitive exclusion principle: 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.
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.
Imagine two populations of fish that live in the same lake and eat the same food.
Suppose Population A can tolerate slightly higher temperatures than Population B. The tolerant Population A will be more likely to survive and reproduce during the summer. Their population size increases and they consume more food. The less tolerant Population B is less likely to survive the increase in temperature; moreover, there is less food to eat. Over time, these disadvantages will only continue to build, and eventually, the size of Population B will decrease.
Of course, a population’s competitive advantage is always relative to its environmental conditions. If the lake’s temperature decreases, Population B might have the competitive advantage and eventually outcompete Population A.
The critical thing to remember here is that any advantage, even small ones, can snowball over time!
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.
Predator: an organism that obtains its food by killing and eating another organism.
Prey: an organism hunted and killed by another organism for food.
There are many examples of predator-prey relationships in nature.
Barn owls are predators that feed on field mice. Barn owls have developed excellent night vision and wide wingspans that allow them to glide silently. On the other hand, field mice have developed colouration that enables them to blend into their environment, as well as highly sensitive hearing and rapid running speeds that increase their chances of escape.
It is important to note that animals can also play both of these roles: we often think about herbivores, like field mice, as prey, but from the perspective of the plants that they eat, they can also be considered as predators!
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.
- The owls eat the mice, which reduces the mice population.
- 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.
- As a result of a reduced predator population, more mice survive and reproduce. The mice population increases again.
- 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.
Competition and Predation - Key takeaways
Competition arises when two or more individuals share a limited resource. There are two types of competition in biology: intraspecific competition and interspecific competition.
Interspecific competition occurs between members of different species.
Intraspecific competition occurs between members of the same species.
According to the competitive exclusion principle, 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.
Predation is a process wherein one organism consumes another organism. The predator-prey relationship follows a cyclical pattern.
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