Nutrients, temperature, disturbance, and evolution: a model for the late Cenozoic marine record of the western Atlantic

Major changes in the marine biota of the western Atlantic region occurred o ver the last five million years, but the causes of these changes, and espec ially the relative roles of changes in temperature and nutrients in affecti ng them, have been controversial. The resolution of this issue has implicat ions beyond this particular time and region because they include two enviro nmental perturbations (the formation of the Central American Isthmus and th e initiation of northern hemisphere glaciation) of global significance. Ana lysis of the western Atlantic late Neogene may also offer insights of broad er significance into how environmental disturbance affects evolution, espec ially the interaction between the processes of extinction and speciation. R eview of available data on paleoenvironments and biotas (including mollusks , corals, foraminifera, ostracodes, marine mammals, sea birds, and sea gras ses) within the context of an explicit theoretical framework for the proces s of allopatric speciation allows construction of a model for evolution in the region during this time. The framework breaks;speciation down into form ation, persistence, and differentiation of isolated populations. The model for the western Atlantic proposes that many of the environmental and change s observed in the record of this region over the past five million years ca n be connected via this framework, especially around the role of environmen tal disturbance; disturbance connects extinction and speciation because the event of speciation may lie on a continuum of disturbance between populati on fluctuation and extinction. Although changes in temperature land perhaps other factors) may have had significant effects, it was change in nutrient conditions - which most likely created conditions of habitat disturbance c onducive to both enhanced speciation and extinction - that played the domin ant role in causing the observed patterns of origination and extinction in the Plio-Pleistocene of the western Atlantic. (C) 2001 Elsevier Science B.V . All rights reserved.