The concept of competition in biology describes a fundamental ecological interaction where organisms struggle against one another for access to limited resources. This struggle is a direct consequence of the fact that the things necessary for survival and reproduction—such as food, water, mates, sunlight, or physical space—are finite within any given environment. The survival and reproductive success of one individual or species inevitably reduces the availability of the resource for others. This pervasive dynamic acts as a powerful selective pressure, shaping the evolution and structure of ecological communities across all biomes.
Competition Within or Between Species Groups
Competition is broadly categorized based on the relationship between the organisms involved, determining whether the conflict occurs within a population or between distinct populations. Intraspecific competition involves individuals of the same species vying for the same limiting resources. For example, two male elk may engage in a physical clash, or “rut,” to secure mating access to females, which represents a limited resource in terms of reproductive opportunity. Similarly, a stand of young pine trees, all belonging to the same species, will compete directly for available sunlight and soil nutrients, leading to the suppression or death of smaller, slower-growing individuals.
Interspecific competition, by contrast, occurs between members of different species that share a reliance on a common resource. A classic terrestrial example involves cheetahs and lions competing over the limited availability of gazelle carcasses on the African savanna. While they are different species, their overlapping dietary needs force a competitive interaction that influences the hunting strategies and population densities of both predators.
Exploitation and Interference
Beyond identifying who is competing, ecologists define competition by the mechanism used to acquire the resources, classified as either exploitation or interference. Exploitation competition is an indirect interaction where organisms deplete a shared resource without ever physically encountering one another. For example, in a marine ecosystem, a dense bloom of phytoplankton may rapidly consume all the available nitrogen in a patch of water. This action makes the nitrogen unavailable to other, slower-growing algal species, effectively outcompeting them simply by using the resource first.
In contrast, interference competition involves direct, aggressive contact or action designed to prevent rivals from gaining access to the resource. A pair of nesting eagles driving away a smaller raptor attempting to hunt in their territory is an example of interference competition for space and hunting rights. Another form involves chemical warfare, such as allelopathy in plants, where one species releases toxins into the soil to inhibit the germination or growth of a competing species nearby.
The Long-Term Results of Competition
Sustained competitive pressure between species has profound, long-term consequences for evolution and community structure, often leading to one of two outcomes. One outcome is described by the Competitive Exclusion Principle, which states that two species cannot coexist indefinitely if they occupy the exact same ecological niche. If their niches overlap completely, the superior competitor will eventually drive the less successful species to local extinction.
However, the more common outcome observed in nature is resource partitioning, which allows similar species to coexist by evolving subtle differences in their resource use. This process involves niche differentiation, where species evolve to utilize slightly different parts of a habitat, consume different sizes of prey, or forage at different times of the day. A classic example involves several species of warblers that coexist in the same forest by feeding in different sections of the same tree, such as one species foraging on the upper branches and another on the lower trunk.
By dividing the limited resource—the total insect population of the tree—into sub-resources, the warblers minimize the intensity of interspecific competition, allowing all populations to persist. This evolutionary divergence, driven by competition, reduces the overlap in their ecological requirements. Resource partitioning thus demonstrates how competition acts as a powerful selective force, promoting specialization and increasing the overall biodiversity that can be supported within a single ecological community.