Ecology is the study of how organisms interact with each other and their surroundings within defined areas called ecosystems. These systems are dynamic, characterized by the cycling of energy and matter, but they are defined by finite boundaries and limited resources. Competition is the fundamental interaction that arises when multiple organisms require the same limited resource for survival, growth, or reproduction. This struggle acts as a powerful selective force that shapes the behavior, physiology, and distribution of species. It is a constant interaction driving the structure of every biological community.
The Two Fundamental Types of Competition
Competition can be categorized based on the relationship between the competing individuals. Intraspecific competition occurs among members of the same species, all seeking the identical resources within the habitat. This type of competition is often the most intense because individuals have nearly identical requirements for food, water, light, and shelter.
For example, a stand of pine trees planted closely together will compete intensely for sunlight and soil nutrients, leading to some trees growing taller and suppressing others. The competition also extends to reproductive success, as males of many species, such as elk, engage in physical contests to gain access to mates. This internal struggle dictates which individuals survive to reproduce, directly influencing the genetic makeup of the next generation.
Conversely, interspecific competition involves individuals of two or more different species. This interaction occurs when the ecological niches of the species—their roles and resource requirements—overlap, forcing them to vie for the same limiting resource. The intensity of this competition depends directly on the degree of niche overlap; the more similar the needs, the stronger the competitive pressure.
A classic example involves predators such as lions and spotted hyenas, which often target the same large ungulate prey in the African savanna. Both species compete for the same recently killed carcass, leading to direct confrontations that determine which group secures the meal. This pressure can significantly influence the population size and geographic range of both participating species.
How Organisms Compete for Resources
The physical act of competition can be divided into two distinct mechanisms. Exploitation competition is an indirect form of interaction where one organism affects another simply by consuming a shared resource first. There is no direct physical engagement; the resource is simply depleted, making it unavailable for others.
A flock of grazing sheep rapidly consuming all the available grass in a pasture is an example of exploitation, leaving nothing behind for any cattle that arrive later. This mechanism is frequently observed in microorganisms, where one bacterial strain may grow faster and use up the available growth medium before a slower-growing strain can establish itself.
In contrast, interference competition involves a direct and often aggressive interaction where one organism actively prevents another from accessing the resource. This mechanism requires a physical or chemical confrontation, ensuring that the resource remains monopolized by the dominant party. Territorial animals like wolves mark and defend a large area, using displays or vocalizations to actively exclude other wolf packs and prevent them from hunting within those boundaries.
Another form is allelopathy, where certain plants secrete toxic biochemicals into the soil to inhibit the germination or growth of surrounding competitors. These agents, such as those produced by the Black Walnut tree, are a direct way for one plant to interfere with the resource uptake of another.
Long-Term Consequences of Competition
Sustained competitive pressure over ecological and evolutionary timescales leads to consequences for species and communities. One outcome is competitive exclusion, which occurs when two species with identical or near-identical resource requirements cannot permanently coexist. If one species is even slightly more efficient at utilizing the shared resource, it will inevitably outcompete the less efficient species.
The superior competitor will experience higher growth rates and reproductive success, eventually leading to the local extinction of the weaker species. This reality confirms that two species cannot occupy the exact same ecological niche indefinitely.
However, competitive exclusion is not the only long-term result; competition often drives evolution toward coexistence through a process known as resource partitioning. This occurs when natural selection favors individuals that slightly modify their resource use, reducing the overlap with their competitors. Over many generations, the species evolve specialized adaptations, effectively dividing the shared resource pool.
A classic example involves five species of warblers in North America that forage in the same spruce trees but specialize in feeding at different heights or on different parts of the branches. By adapting to use different segments of the same habitat, they minimize direct competition and successfully coexist. This evolutionary shift toward specialization is also called niche differentiation. The pressure to avoid direct competition fuels this specialization, leading to changes in morphology, such as differences in beak size in finches or shifts in body size in predatory mammals across different habitats. These physical adaptations allow species to become highly efficient at exploiting a specific subset of resources, thus avoiding confrontation with others.