Size-asymmetric competition refers to situations in which larger individuals exploit disproportionately greater amounts of resources when competing with smaller individuals. This type of competition is common among plants but also exists among animals. Size-asymmetric competition usually results from large individuals monopolizing the resource by "pre-emption". i.e. exploiting the resource before smaller individuals are able to obtain it. Size-asymmetric competition has major effects on population structure and diversity within ecological communities.