Evolutionary paleoecology of dense ophiuroid populations

Abstract

Issues of scale are becoming increasingly important to paleobiological interpretations of the fossil record. Nevertheless, a number of biological processes display scale-independent behaviors. The effects of predation on the distribution of dense populations of epifaunal, suspension-feeding ophiuroids are scale-independent, at scales ranging from the microecological to the macroevolutionary. On a microecological scale (meters to kilometers, hours to days), dense ophiuroid populations are limited in shallow-water environments by predatory fishes and crabs. On a larger, ecological scale (tens to hundreds of kilometers, decades to centuries), circumstantial evidence indicates that oceanographically driven, multidecadal cycles of predator abundance determine the abundance of ophiuroids throughout the western English Channel. On a macroevolutionary scale (millions to tens of millions of years, global spatial scale), dense, autochthonous assemblages of ophiuroids declined in conjunction with the Mesozoic diversification of modern shell-crushing predators: teleostean fishes, decapod crustaceans, and neoselachian sharks. The sporadic reappearance of dense ophiuroid populations in a late Eocene, shallow marine deposit in Antarctica suggests that predator-prey relationships were disrupted as temperatures declined in the region at that time. Scale-independence is a useful model for explaining and predicting patterns of distribution of dense ophiuroid populations in time and space.