<P> Competition is an interaction between organisms or species in which both the organisms or species are harmed . Limited supply of at least one resource (such as food, water, and territory) used by both can be a factor . Competition both within and between species is an important topic in ecology, especially community ecology . Competition is one of many interacting biotic and abiotic factors that affect community structure . Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition . Competition is not always straightforward, and can occur in both a direct and indirect fashion . </P> <P> According to the competitive exclusion principle, species less suited to compete for resources should either adapt or die out, although competitive exclusion is rarely found in natural ecosystems . According to evolutionary theory, this competition within and between species for resources is important in natural selection . However, competition may play less of a role than expansion among larger clades; this is termed the' Room to Roam' hypothesis . </P> <P> Competition occurs by various mechanisms, which can generally be divided into direct and indirect . These apply equally to intraspecific and interspecific competition . Biologists typically recognize two types of competition: interference and exploitative competition . During interference competition, organisms interact directly by fighting for scarce resources . For example, large aphids defend feeding sites on cottonwood leaves by ejecting smaller aphids from better sites . In contrast, during exploitative competition, organisms interact indirectly by consuming scarce resources . For example, plants consume nitrogen by absorbing it into their roots, making nitrogen unavailable to nearby plants . Plants that produce many roots typically reduce soil nitrogen to very low levels, eventually killing neighboring plants . </P>

Give examples of how one species may depend on another