Interspecific competition refers to competition between individuals of different species, while intraspecific competition occurs among individuals of the same species. Intraspecific competition is generally more effective at limiting population size due to the fact that individuals within a species share similar resource needs, behaviors, and ecological niches. This similarity leads to more direct competition for limited resources such as food, territory, and mates. When resources become scarce, intraspecific competition can result in significant population regulation through mechanisms like reduced reproduction, higher mortality rates, and increased dispersal among individuals of the same species.
In contrast, interspecific competition often involves species with different ecological requirements and adaptations. While it can influence community dynamics, the impact on population size tends to be less pronounced because the competing species might utilize resources differently or occupy distinct niches. As a result, the competitive pressure is diluted, and populations are less likely to experience the same degree of regulation as seen within a species. Therefore, intraspecific competition typically plays a more crucial role in population size limitation, particularly in densely populated settings where resources are highly contested.