Competition

"When populations of two or more species in a community rely on similar limiting resources, they may be subject to interspecific competition. Competition can occur in different ways. Actual fighting over resources is termed interference competition, whereas the consumption or use of similar resources is called exploitative competition. The density-dependent effects of interspecific competition are similar to those of intraspecific competition. As population densities increase, every individual has access to a smaller share of some limiting resource; as a result, mortality rates increase, birthrates decrease, and population growth is curtailed. In interspecific competition, however, the population growth of a species may be limited by the density of competing species as well as by the density of conspecifics. For example, if several bird species in a forest feed on a limited population of insects, the density of each species may have a negative impact on population growth in the others. Similarly, species may compete for nesting sites, shalters, or any resource that is in short supply."

SOURCE: Campbell, N.A., Reece, J.B. and L.G. Mitchell. 1999. Biology, 5th ed. Benjamin Cummings, Menlo Park, CA. pp. 1114-1115.

Exploitative competition is a major element in the interaction between invasive and native species. For example, purple loosestrife (Lythrum salicaria), an invasive plant (introduced from Europe by humans) that thrives in wetlands, is able to out-compete native marsh plants like cattails (Typha sp.) for space because it has a wider environmental tolerance range and can reproduce very rapidly via both seed dispersal and vegetative propagation. In this example space in which to grow and access sunlight for photosynthesis is the limiting resource being competed for. Unlike purple loosstrife, native cattails are an important source of food for many wetland animals.

Cattail (Typha latifolia).

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