E15 Competition

Topic

Plant competition occurs when multiple plants require the same shared resources—light, water, nutrients, or space—and those resources are insufficient for every plant to obtain the amount it would need if growing in isolation; fundamentally, plant competition is a physical process involving the differential acquisition of these shared resources.

Among the shared resources for which plants compete, the limiting resource is the one that is depleted first relative to the plants' needs, and it is also the factor that ultimately determines the outcome of the competition: the plant that captures the limiting resource more efficiently than the others eventually excludes its competitors, as the latter fail to secure enough of that resource to sustain themselves. This concept can be summarized by the idea that each species requires a minimum level of a resource to survive in the face of competition; the species with the lowest minimum resource requirement is the one that ultimately excludes the others when competing for the same limiting resource.

For two or more species to coexist rather than one excluding the other over the same limiting resource, a mechanism of coexistence is required; the primary mechanism is niche differentiation. Instead of acquiring the exact same shared resource in the same way, each species captures a distinct portion of the shared resources—whether by accessing the resource at a different location, at a different time, or through a different method of acquisition than its competitors. The greater the niche differentiation between two species, the lower the competitive overlap—that is, the smaller the fraction of shared resources for which both species actually compete—and the lower the probability that one will eventually exclude the other; depending on the degree of niche differentiation between the species involved, competition for the same shared resources results either in the exclusion of the species with the higher minimum resource requirement or in the coexistence of multiple species that partition those shared resources in different ways.

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