Organisms within an ecosystem constantly interact, forming intricate relationships. These interactions can take many forms, but one fundamental force is competition. Competition occurs when different species vie for the same finite resources, influencing their populations and distribution. This dynamic interplay helps determine which species thrive and which may decline.
Defining Competitive Exclusion
The competitive exclusion principle, also known as Gause’s Law, states that two species competing for the exact same limited resources cannot stably coexist. If two species occupy identical ecological niches—meaning they use the same resources in precisely the same way—one will inevitably outcompete the other over time. The species with even a slight advantage in resource acquisition or utilization will eventually dominate. This process typically leads to one of two outcomes: either the less competitive species faces local extinction, or it undergoes an evolutionary or behavioral shift to utilize different resources or occupy a different part of the habitat.
Conditions for Competitive Exclusion
For competitive exclusion to occur, several specific conditions must be present in an environment. First, the competing species must occupy nearly identical ecological niches. The resources in question must also be limited; if resources are abundant enough to support both populations indefinitely, direct competition leading to exclusion is less likely to happen.
The environment needs to remain relatively stable for a sufficient period, allowing the competitive interaction to fully unfold. Constant environmental disturbances might disrupt the competitive process, potentially allowing less competitive species to persist. Competitive exclusion is most probable when competition for shared resources is the primary factor limiting the growth and survival of both species. If other factors, such as predation or disease, regulate populations more strongly, the effects of resource competition might be less pronounced.
Examples in Nature
Classic experimental evidence for competitive exclusion comes from studies involving Paramecium species. In laboratory settings, when Paramecium aurelia and Paramecium caudatum are grown separately with ample food, both populations thrive. However, when placed together in the same container with limited resources, P. aurelia consistently outcompetes P. caudatum for food, leading to the eventual decline and elimination of the P. caudatum population. This demonstrates how a slight competitive advantage can lead to one species dominating.
Another example is the introduction of the gray squirrel (Sciurus carolinensis) to Britain, where it has largely replaced the native red squirrel (Sciurus vulgaris). Both species compete for similar food resources. The gray squirrel is more efficient at foraging and can digest unripe acorns, a food source less accessible to red squirrels, giving it a competitive edge. Similarly, invasive species like Asian carp in North American waterways can outcompete native fish for food, altering ecosystems and threatening local species.