Biology Competition Concepts

An interaction between two individuals that has a negative impact on both.

Competition between individuals of the same species.

Competition between individuals of different species.

Anything an organism consumes or uses that causes an increase in the growth rate of a population when it becomes more available.

A resource that is constantly regenerated.

A resource that is not regenerated.

A population increases until the supply of the most limiting resource prevents it from increasing further.

The species that can persist at the lowest resource level will win the competition.

Competition is most intense between closely related species because they share similar traits and likely consume similar resources.

The ability of one species to persist at lower levels of a resource compared to another species.

When two species compete for a single limiting resource, the species that can persist at the lowest resource level will win the competition.

The ability of one species to outcompete another species for a shared resource.

A type of competition where individuals compete indirectly for resources by consuming them.

A type of competition where individuals interfere with each other’s access to resources.

A type of competition where two species appear to be competing, but their interactions are actually mediated by a shared predator.

The ability of a species to persist under harsh conditions, such as extreme temperatures or low water availability. This can enable a species to outcompete others even if they are not as strong in resource acquisition.

Sudden events that can disrupt the balance of a community, such as fires, floods, or storms. These events can create opportunities for species that are better adapted to disturbance.

Interactions where one species benefits by eating another, such as predation (animals) or herbivory (plants). Predators or herbivores can influence competition by selectively removing certain species.

Organisms can face trade-offs between traits. Being good at competition might make them vulnerable to predation, and vice versa. This can lead to an evolutionary balance.

The change in the outcome of competition due to the presence of predators or herbivores. The species that is better at avoiding predation can become more dominant.

An example of predation altering competition. Spadefoot tadpoles are more active and outcompete other tadpoles for food. But when predators are present, the less active peepers have a higher survival rate.

Herbivory can also alter competition. Goldenrod plants can outcompete others by growing tall. But a specific beetle eats goldenrod, leading to a more diverse plant community.

A study where plots of land were treated with insecticide. Insecticide removed the beetle that eats goldenrods, resulting in the dominance of goldenrod. This demonstrates the impact of herbivory on competition.

When abiotic conditions are harsh, they can favor species adapted to those conditions, even if they are not the best competitors for resources. This can influence the outcome of competition.

The presence of predators or herbivores can significantly affect the balance of competition. The species that is better at avoiding them might become more dominant, even if it wasn't the strongest competitor.

The logistic growth model, which describes how populations grow and stabilize, is extended to model competition between two species for a single resource.

The carrying capacity of an environment is the maximum population size that it can sustainably support. In the case of interspecific competition, this carrying capacity needs to be considered for both species.

Competition coefficients, denoted by α and β, convert the number of individuals of one species into an equivalent number of individuals of the other species. These coefficients represent how the presence of one species affects the carrying capacity experienced by the other.

The competition coefficient α measures how many individuals of species 2 are equivalent to one individual of species 1 in terms of resource consumption. For example, if α is 0.5, it means that one individual of species 1 uses the same amount of resources as 0.5 individuals of species 2.

The competition coefficient β measures how many individuals of species 1 are equivalent to one individual of species 2. For example, if β is 2, it means that one individual of species 2 uses the same amount of resources as 2 individuals of species 1.

A zero population growth isocline represents the combinations of population sizes for two species where the population growth rate of one species is zero. It helps us predict the outcome of competition because it shows where the population is stable for each species.

The zero population growth isocline for species 1 shows the combinations of population sizes for species 1 and species 2 where the population growth rate of species 1 is zero. The x-intercept represents carrying capacity for species 1 when there are no individuals of species 2.

The zero population growth isocline for species 2 shows the combinations of population sizes for species 1 and species 2 where the population growth rate of species 2 is zero. The x-intercept represents carrying capacity for species 2 when there are no individuals of species 1.

The outcome of competition between two species depends on the relative positions of their zero population growth isoclines. If one isocline is above the other, the species with the higher isocline will outcompete the other, leading to the extinction of the lower species.

If the zero population growth isoclines for two species intersect, the outcome of competition depends on the initial population sizes of the two species. Depending on the initial population sizes, one or the other species will outcompete the other.

If the zero population growth isoclines for two species intersect and the carrying capacities (K1 and K2) are the most extreme points on the axes, the outcome of competition depends on the initial population sizes. One species will eventually win and outcompete the other.

If the zero population growth isoclines for two species intersect and the carrying capacities (K1 and K2) are the innermost points on the axes, the two species are likely to coexist. This occurs when interspecific competition is weaker than intraspecific competition, meaning each species primarily competes with its own kind.

The outcome of competition is not always determined by a single resource. When species compete for multiple resources and have overlapping niches, the outcome can be more complex and less predictable.