<P> Apparent competition is actually an example of predation that alters the relative abundances of prey on the same trophic level . It occurs when two or more species in a habitat affect shared natural enemies in a higher trophic level . If two species share a common predator, for example, apparent competition can exist between the two prey items in which the presence of each prey species increases the abundance of the shared enemy, and thereby suppresses one or both prey species . This mechanism gets its name from experiments in which one prey species is removed and the second prey species increases in abundance . Investigators sometimes mistakenly attribute the increase in abundance in the second species as evidence for resource competition between prey species . It is "apparently" competition, but is in fact due to a shared predator, parasitoid, parasite, or pathogen . </P> <P> Many studies, including those cited previously, have shown major impacts on both individuals and populations from interspecific competition . Documentation of these impacts has been found in species from every major branch of organism . The effects of interspecific competition can also reach communities and can even influence the evolution of species as they adapt to avoid competition . This evolution may result in the exclusion of a species in the habitat, niche separation, and local extinction . The changes of these species over time can also change communities as other species must adapt . </P> <P> The competitive exclusion principle, also called "Gause's law" which arose from mathematical analysis and simple competition models states that two species that use the same limiting resource in the same way in the same space and time cannot coexist and must diverge from each other over time in order for the two species to coexist . One species will often exhibit an advantage in resource use . This superior competitor will out - compete the other with more efficient use of the limiting resource . As a result, the inferior competitor will suffer a decline in population over time . It will be excluded from the area and replaced by the superior competitor . </P> <P> A well - documented example of competitive exclusion was observed to occur between Dolly Varden charr (Trout) (Salvelinus malma) and white spotted char (Trout) (S. leucomaenis) in Japan . Both of these species were morphologically similar but the former species was found primarily at higher elevations than the latter . Although there was a zone of overlap, each species excluded the other from its dominant region by becoming better adapted to its habitat over time . In some such cases, each species gets displaced into an exclusive segment of the original habitat . Because each species suffers from competition, natural selection favors the avoidance of competition in such a way . </P>

Which is an abiotic factor that would affect the ability of a species of tree to survive