Export flux and stability as regulators of community composition in pelagic marine biological communities: Implications for regime shifts

Regime shifts occur when a system transitions from one stable configuration to another. Such abrupt changes in biological communities may reflect small changes in environmental conditions such as temperature, oxygen concentration, or irradiance. Although it seems clear that biological communities are not randomly organized with respect to their functional components, there is disagreement concerning the factors that control that organization. In this paper, I examine the implications of assuming that the composition of pelagic marine biological communities evolves to a condition of maximum stability or resilience. At temperatures of 25 °C or less, a model based on this hypothesis predicts abrupt and discontinuous transitions from configurations associated with low export ratios to configurations associated with high export ratios as the rate of primary production increases. Comparison between field data and model predictions shows very good agreement at low and high production rates, but the field data do not support a step-function transition from low to high export ratios at intermediate rates of production. Instead, the field data are consistent with the assumption that food webs effect the transition between high and low ef ratio modes by reconfiguring themselves in a more-or-less continuous manner. The configurations associated with these transitions are at least locally more resilient than any similar food web structure.