Practice question

In the tolerance model of succession, any species capable of reaching a site may establish without needing earlier residents to improve the environment. Early and late species can therefore colonize independently, but later-successional species eventually dominate because they tolerate lower resource levels, live longer, or compete more effectively under conditions such as shade. Their success is not caused by facilitation; neither is establishment necessarily blocked by incumbents. Facilitation instead requires pioneers to create conditions needed by successors. Inhibition gives residents a negative priority effect, making later establishment difficult until the first occupants die or are disturbed. The phrase “persist without help” captures tolerance only if it means colonization does not depend on previous species. It should not imply that every colonist remains forever: competitive replacement is central to the model. Dispersal still matters because a tolerant species cannot establish if it never arrives. Thus, independent establishment combined with eventual replacement according to life-history and competitive traits explains why tolerance is the appropriate successional mechanism.