The struggle among organisms for limited resources—such as food, water, or territory—is a fundamental process that shapes every ecosystem. This rivalry, known as ecological competition, dictates which species can thrive and influences the traits passed down through generations. When demand exceeds supply, organisms most efficient at obtaining resources survive and reproduce. This pressure drives much of the observable behavior and population dynamics in the natural world.
Understanding Competition Between Different Species
Competition is categorized based on the relationship between the organisms involved. Intraspecific competition occurs when individuals from the same species vie for the same resource, such as two male deer fighting over territory. Interspecific competition, the focus here, involves two different species competing for the same limiting food source. This interaction occurs when the ecological niches of two species—their roles and resource requirements—overlap significantly. If food is abundant, species may coexist, but scarcity intensifies the negative interaction, placing selection pressure on both populations.
Real-World Examples of Food Competition
A classic example of interspecific food competition occurs on the African savanna between the lion and the spotted hyena. Both species are carnivores that hunt large ungulates. They frequently compete over the same carcass, with hyenas often attempting to steal a kill from lions or vice versa. This direct, interference-based competition uses physical confrontation to determine which animal secures the resource.
In aquatic environments, competition often centers on plankton. In North American rivers, the introduced Bighead carp competes directly with native filter-feeders, such as the Paddlefish and larval Bluegill, for zooplankton. The carp’s rapid growth and efficient filter-feeding mechanism deplete zooplankton populations. This indirectly reduces the food available for native species, negatively affecting their growth and survival rates.
Herbivores also engage in this struggle, particularly large grazers that share a range. The Apennine chamois experiences increased competition from the larger Red deer in parts of its European range. Both species primarily consume ground-level forage. When Red deer populations increase, they reduce the available browse, including nutritious forbs and grasses. This resource depletion forces the smaller chamois to use lower-quality food, which decreases the winter survival rate of chamois young.
How Species Adapt to Avoid Direct Conflict
Intense, prolonged interspecific competition has two main outcomes: one species may be completely outcompeted, or both species may evolve to reduce their niche overlap. The Competitive Exclusion Principle states that two species cannot indefinitely occupy the exact same ecological niche; one will eventually prevail. More often, species evolve behaviors or traits that lead to resource partitioning, a mechanism to lessen direct conflict.
Resource partitioning involves species using the same resource in slightly different ways. For example, two bird species might eat the same insects from the same tree, but one forages on upper branches while the other feeds on the lower trunk. This differentiation can also be temporal, with one species becoming nocturnal and the other diurnal. By specializing in a fraction of the total resource, both species can coexist, promoting greater biodiversity.