Competition is a fundamental biological interaction that drives evolution and shapes ecological communities across the planet. This interaction occurs when two or more organisms require a resource that exists in a limited supply within their shared environment. The necessity of obtaining these finite resources, such as light, water, or mates, creates a constant selective pressure. Organisms must continually adapt to better secure what they need to survive and reproduce.
Defining the Struggle for Limited Resources
Competition is formally defined in ecology as an interaction where two organisms require a resource that is in limited supply, such as food, water, light, or territory. The presence of one organism reduces the resource available to the other, negatively affecting the fitness (growth, survival, or reproduction) of both parties involved. A species’ ecological role, or its “niche,” is defined by the full range of resources it uses and the conditions it can tolerate. When the niches of two organisms overlap, they vie for the same limited resource, and the intensity of this struggle increases as the supply decreases. This interaction serves as a powerful mechanism for regulating population sizes and structuring biological communities.
Competition Within a Single Species
Competition occurring among individuals of the same species is known as intraspecific competition. Since members of the same species share nearly identical resource requirements, this competition is often the most intense form of biological rivalry. A highly visible example is the contest competition seen when two male red deer clash antlers during the rutting season. These physical contests determine which individual gains access to females, thus securing mating rights and passing on its genes.
Another example involves trees of the same species, such as oaks, growing close together in a dense forest. Here, the competition is for sunlight and soil nutrients, a form of struggle known as scramble competition. Taller trees intercept more solar energy, limiting the light available to their shorter neighbors, which can stunt the growth and survival of less successful individuals.
Similarly, grizzly bears compete for prime fishing locations along a river during the salmon spawning run. Dominant bears occupy the most productive spots, forcing other bears to use less advantageous areas. This directly impacts the food intake and overall health of the subordinate bears.
Competition Between Different Species
Interspecific competition describes the rivalry that takes place between members of two or more different species. This interaction arises when distinct species attempt to use the same limited resource within the same habitat. A classic illustration occurs on the African savanna, where lions and spotted hyenas often compete for the same prey, such as zebras or wildebeest. Both species are negatively affected because the presence of the other reduces the overall availability of food.
Different species of barnacles on a rocky shoreline provide an example of competition for space, a resource necessary for attachment and filter feeding. One barnacle species may grow faster or settle more effectively, preempting the space and preventing other species from establishing themselves. This struggle can lead to competitive exclusion, where one species is so successful that it drives the competing species out of the local area.
Invasive species, such as purple loosestrife in wetlands, demonstrate competitive exclusion. They aggressively outcompete native plants for water and nutrients, leading to a reduction in the diversity of the native flora.