Competition for food is a fundamental interaction in nature, occurring when organisms require resources that are available in limited supply. This dynamic arises because the demand for food often exceeds its availability within an environment. When animals vie for the same finite food source, the presence of one animal can reduce the amount of food accessible to another. This interaction can influence the health and reproductive success of the individuals involved.
Types of Competition for Food
One primary form is interspecific competition, which occurs between individuals of different species for the same limited food resources within an ecosystem. For instance, a predator species might compete with another predator species for the same prey animals.
Intraspecific competition takes place among individuals of the same species. This form of competition is often more intense because they have nearly identical resource requirements. A population of deer grazing in a forest, for example, will all compete for the same available woody plants and forage. Both types of competition play a role in regulating populations and shaping ecological communities.
Examples of Food Competition in Nature
In African savannas, lions and spotted hyenas engage in interspecific competition for prey, as both species hunt similar large herbivores like zebras and wildebeest. This rivalry means that the presence of one species can reduce the food available to the other. Similarly, on grasslands, cows and horses can compete for the same grass, even though they are different species.
Intraspecific competition is also prevalent. During winter, deer populations often feed on woody trees, and as the population grows, individual deer indirectly compete for this limited food source. In aquatic environments, various fish species, including schooling fish, compete for food resources like zooplankton, showcasing intense scramble competition. Even within a single pond, a high density of tadpoles will compete for food, potentially suppressing their growth and development.
Strategies Animals Use to Compete for Food
One direct method is interference competition, where individuals actively prevent others from accessing food. This can involve aggressive behaviors like fighting, territorial defense, or displays of dominance to exclude rivals. For example, larger, dominant grizzly bears often claim the best fishing spots during salmon runs, preventing smaller bears from accessing prime locations.
Exploitative competition is an indirect strategy where individuals consume resources quickly and efficiently, thus reducing the availability for others without direct interaction. Grazing animals, like cows, demonstrate this as they consume grass, leaving less for others in the herd. Competitive interactions can also be categorized as “scramble” or “contest.” Scramble competition involves a shared, limited resource where all competitors have access, but the quantity per individual declines with increasing population density. Contest competition involves individuals gaining exclusive access to a resource.
Ecological Outcomes of Food Competition
One such outcome is the competitive exclusion principle, which suggests that two species cannot coexist indefinitely if they compete for the exact same limited resources. If one species has even a slight advantage, it can outcompete the other, potentially leading to the local displacement or extinction of the less successful competitor. For instance, laboratory experiments with two Paramecium species showed that one could outcompete the other for food, leading to its elimination.
To avoid such exclusion, species often evolve through resource partitioning, differentiating their ecological niches. This involves using different parts of a shared resource, utilizing it at different times, or occupying distinct areas of a habitat. Anole lizards in the Caribbean, for example, have diversified to use different types and heights of vegetation, reducing direct competition for food and allowing multiple species to coexist. Competition also influences population dynamics, as limited food resources can restrict population growth and size.