Practice question

Stable coexistence requires mechanisms that reduce average interspecific competition or create stabilizing advantages when a species becomes rare. Niche differentiation and complementarity achieve this by allowing species to use different resources, places, or times, thereby limiting direct overlap. If the number of independently limiting resources or niche dimensions is sufficiently large relative to competitors, classical resource-competition theory can also permit coexistence, though the wording given is simplified. Niche overlap, by itself, is not a coexistence mechanism; it indicates shared use and can intensify competition when the shared resource is limiting. Partial overlap is compatible with coexistence when other stabilizing processes operate, but increasing overlap does not explain that stability. Competitive exclusion is most likely when species have nearly identical requirements and no fitness or stabilizing trade-off. Modern coexistence theory separates niche differences, which generate negative frequency dependence, from average fitness differences, which favor one species. Coexistence occurs when stabilizing niche differences are strong enough to overcome those fitness inequalities. Thus overlap describes potential competitive similarity rather than a process that maintains diversity.