Disturbance and Ecologic Succession in an Upper Ordovician Cobble-Dwelling Hardground Fauna

An Ordovician hardground fauna in northern Kentucky provides an example from the fossil record of the maintenance of species diversity by periodic disturbance of an autogenic ecologic succession. The marine invertebrates found encrusting limestone cobbles show an order of community development from a low-diversity pioneer assemblage through a high-diversity association to a monospecific stable fauna. All species, including the late successional dominants, were present in the early stages of colonization. Periodic overturning of the cobbles killed the encrusters and opened up new spaces on which succession was reinitiated. These disturbances maintained high diversity within the encrusting community the spatial distribution of the most efficient space competitor.