In the absence of competition, both a small and a large species might evolve towards an intermediate size. This is known as ecological release . Whether one is observing character displacement or ecological release then depends on the order and independence of speciation events. This is hard to know, but a good cladogram would resolve the issue. Summary - The Consequences of Competition Competition can be a powerful force affecting the growth, distribution, and abundance of populations in nature.
Field experiments provide strong evidence of competition in nature.
Often, one species is the superior competitor, the other is better able to withstand certain environmental extremes. Competition is a powerful force of natural selection. Genetic variation in a character that influences competition, coupled with selection to reduce competitive overlap, make a strong argument for the evolutionary divergence of characters. Competition likely affects species diversity. In the short run, competition should cause a reduction in the number of species living within an area, preventing very similar species from co-occurring.