Competition in nature refers to an interaction between organisms or species where the presence of one individual or species reduces the fitness of another. This occurs when both require one or more resources that are in limited supply, such as food, water, or territory.
Forms of Competition
Competition is broadly categorized into intraspecific and interspecific types. Intraspecific competition involves individuals of the same species vying for shared resources, such as plants competing for sunlight, water, or nutrients as their density increases. Interspecific competition occurs between different species that require similar limited resources, such as lions and leopards competing for similar prey, or weeds competing with rice plants.
Specific mechanisms describe how competition unfolds. Consumption competition, also known as exploitation competition, happens indirectly when organisms consume a shared limited resource. For instance, day-active and night-active species might compete for the same food source without direct encounter. Interference competition involves organisms directly interacting to prevent others from obtaining resources. This involves aggressive behaviors, such as large aphids ejecting smaller aphids from feeding sites, or male red deer fighting during rut.
Overgrowth competition occurs when one organism grows physically over another, depriving it of resources like light or space. An example is the Kudzu plant, which rapidly grows over other plants and trees. Chemical competition, or allelopathy, involves organisms releasing biochemicals that inhibit competitors’ growth, survival, or reproduction. Certain Salvia plants, for example, release volatile compounds into the soil that suppress the growth of surrounding plants.
Ecological Principles of Competition
The competitive exclusion principle, also known as Gause’s Law, is a fundamental ecological concept stating that two species competing for the same limited resource cannot coexist indefinitely. If their ecological niches are identical, one species will outcompete and eliminate the other. An experimental demonstration involved two species of protozoans, Paramecium aurelia and Paramecium caudatum. When grown separately, both thrived, but when placed together with a fixed food source, P. aurelia consistently outcompeted P. caudatum, leading to the latter’s decline.
To avoid competitive exclusion, species often engage in niche partitioning, also called resource partitioning, allowing coexistence through specialization in shared resources. This can involve using different parts of a habitat, utilizing resources at different times, or consuming different types of the same resource. For instance, several warbler species can coexist in the same forest by foraging for insects in different parts of the same tree, such as the top canopy versus lower branches.
Another example is Darwin’s finches on the Galápagos Islands, where different species have evolved distinct beak sizes and shapes, allowing them to specialize in consuming different sizes of seeds, reducing direct competition for food. Similarly, Anole lizards on Caribbean islands occupy distinct microhabitats within trees, with some living in the canopy and others closer to the ground, thereby partitioning space and allowing multiple species to thrive. This division of resources is a significant mechanism for reducing direct competition and supporting biodiversity.
Role in Biodiversity and Evolution
Competition acts as a powerful driver of natural selection and adaptation within ecosystems. Individuals with traits that confer a competitive advantage, such as better foraging efficiency or greater resistance to toxins, are more likely to survive, reproduce, and pass those advantageous traits to their offspring. Over generations, this leads to the increased prevalence of beneficial traits within a population, shaping the evolution of species to become better suited to their environments. For example, plants that grow taller or develop broader leaves may gain a competitive edge for sunlight in a dense forest, influencing the genetic makeup of future plant generations.
Competition also influences community structure by determining which species can coexist and at what population densities. While intense competition can lead to competitive exclusion, reducing species diversity, it can also foster diversity through niche partitioning and specialization. By encouraging species to occupy distinct ecological roles, competition allows a greater variety of life forms to share the same habitat.
Strong competition can also promote speciation through a process known as character displacement. This occurs when similar species whose geographical ranges overlap evolve more pronounced differences in traits related to resource use in areas where they co-occur, compared to areas where they live separately. For instance, Darwin’s finches on islands where two species coexist often show greater differences in beak size, leading to specialization on different seed types and reducing interspecific competition, which can contribute to the formation of new species over long periods. Thus, competition plays a dual role, potentially leading to local extinction but also fostering diversification and the intricate web of life.