Species Competition

ADVERTISEMENT

Species competing for living space, water, and food is called interspecific competition. When resources are abundant in a habitat, competition is minor or does not take place at all, but when resources become scarce, interspecific competition becomes a critical factor in determining whether an endangered animal lives or dies. Invasion may cause resources to become so scarce, in fact, that members of the same species begin to compete to stay alive, an event known as intraspecific competition. In addition to food, water, and space, plant or animals also compete over the following things in both healthy habitats and invaded habitats: sunlight, grazing land, soil nutrients, migration corridors, nesting sites, den sites, shelter, and hiding places.



Two or more species that live in the same habitat and use the same resources can coexist without competing. Specialists do not have much flexibility in resource use, but generalists can adjust their uses to avoid competition. Niche overlap occurs when two species use the same resource in identical ways. No overlap results in resource partitioning, which is advantageous for the strict Specialist 2 in this diagram.

Severe direct competition between species causes extinction of one of them in a situation known as competitive exclusion. In competitive exclusion, one species’ population outcompetes another species’ population vying for the same space and food, leading to a local extinction of the loser. Perhaps the two species simply cannot devise a way (by adapting) in which both can thrive in the same ecosystem. Usually the more adaptive species wins, and the loser is then considered the less fit organism for the ecosystem. The defeated species must then migrate to a new habitat or
become extinct.

Migration may not favor some animals, however, because it leaves them vulnerable to new environmental stresses, diseases, and predators. For that reason some animals have devised ways to avoid competition altogether. This avoidance serves two purposes: They save energy by not competing, energy that can be used for other daily activities, and they avoid mass migrations. Two means by which animals avoid competition are by sharing resources or by finding a unique niche.

Resource partitioning allows two different animal species to share the same resource in a slightly different manner. For example, wolves and coyotes compete, yet they find ways to share the habitat by focusing on different hunting techniques. Coyotes often hunt alone and for small mammals; wolves hunt in packs to prey on much larger animals such as elk. Though each species can subsist on the other’s main food source, they focus on the resource less likely to interest their competitor.

Other species avoid competition by seeking a unique niche in a process called niche specialization. In niche specialization, two species develop specialties that allow them to occupy separate niches in the same ecosystem.
As they evolve toward these distinct niches, they reach a point in which neither species need compete directly with the other. For example, plovers and sandpipers are birds that both live along beaches. Plovers have evolved large eyes and short, strong beaks for finding crustaceans on the sand’s surface. Meanwhile, sandpipers hunt the same sands as the plovers. Sandpipers have much smaller eyes than plovers so depend less on sight for hunting, but they do possess much longer beaks that probe deep into the sand for food the plovers cannot reach. The following table describes
the discrete adjustments that species make to share an ecosystem or a habitat.



The associations between different species represent symbiosis, which is a cooperative relationship between dissimilar species; it may be thought of as the opposite of competition. Symbiotic relationships may be between two animals or they may be plant-animal, plant-plant, microbe-animal, or microbe-plant. Two main types of symbiosis between species in ecosystems are mutualism and commensalism. In mutualism, two species interact in a way that benefits both. Bacteria living inside an animal’s intestines provide an example of a mutualistic relationship because the bacteria receive nourishment while helping the host digest food. In commensalism, one species benefits and the other is neither helped nor harmed. When barnacles attach to gray whales, they catch food as the whale swims, but the whale is unaffected. Parasitism occurs when one species benefits but the other is harmed, such as ticks living on a coyote.