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In an ecological community, the species which is most numerous and forms the bulk of biomass may be considered the dominant species. Ecological dominance may also be defined as the species that has the most influence on other species in the same environment. Dominant species include plants and animals that influence the ecological conditions of an environment by their size, abundance, or behavior and determine which other animals or plants can survive in that environment. In some environments, there may be one or more dominant species.
Good examples of ecological domination in the plant world are the forest communities of the Rocky Mountains. After a forest fire, plants and trees progress through various stages, with small plants like grasses and ferns growing back first. Eventually, small trees like aspen and birch take root and sprout upward cutting off sunlight from those smaller ground plants on the forest floor. After a number of years, coniferous trees like pines and spruces will grow above the smaller trees. At each stage of growth, one species of plant succeeds the previous species and, for a time, exists as the dominant species in the forest ecosystem.
In the animal kingdom, the top predator may become the dominant. A good example is the Yellowstone Lake ecosystem in Wyoming, where predatory lake trout were illegally introduced in 1994. Prior to the introduction of the piscivorous, or fish eating, lake trout, the Yellowstone cutthroat trout was the dominant species in the lake ecosystem. In 2011, if not controlled, lake trout could reduce the Yellowstone cutthroat trout population by as much as 90% over the next 20 years and might eliminate them completely. The lake trout would then be considered the dominant fish in this ecological community.
The top predator might not always be the top species, though. Sometimes a species attains dominance through sheer numbers, and in this case, the total biomass of a species makes it the dominant one. Large numbers of a single species can exert tremendous influence on an ecosystem. One simple example of this would be a locust infestation in a wheat field. With an abundant food supply and no predators, a population of locusts can increase its numbers over a very short period of time, becoming the dominant species in this ecosystem.