Biotic Effects of Sea Level Change: the Pleistocene Test

Species diversity change, and therefore compositional changes in a biota, may be associated with changes at any of three ecological evels, involving the number of provinces within the biosphere, of communities within provinces, and of species represented within communities. Pleistocene sea level changes did not much affect the marine biosphere at any ecological level. An analysis of an extensive data set of Californian Pleistocene and Recent mollusks indicates a continuity of community and species composition during highstands of the last million years. Extensive latitudinal shifts in species' geographic ranges, associated with climatic change and not with sea level itself, created the most significant biotic changes. Extinctions were minimal, well below predicted species=area effects. Evidently, only "perched" faunas are particularly vulnerable to sea level change. Although sea level falls are commonly associated with a faunal hiatus, changes associated therewith can be referred to sea level change itself only in limited situations, and other paleobiologic explanations should be sought in most cases.