Non-linear dynamics in marine-phytoplankton population systems

Although non-linear density-dependence has been widely emphasized in population dynamics studies, the existence of non-linear exogenous forces have been less explored. In particular, we propose that the formulation of population dynamics models that include both non-linear endogenous (i.e. feedback structure) and exogenous (e.g. climatic) responses is relevant for understanding how climate variability affects natural systems. Here we show that single-species non-linear logistic models for marine phytoplankton in combination with non-linear exogenous forces capture observed population oscillations very well. Our results suggest that general population dynamic theory represents a useful tool for understanding the natural fluctuations of phytoplankton populations. Altogether we document what might be called a switch-on/switch-off dynamics in the phytoplankton population dynamics in relation to climate variability. We suggest the importance of, and the need for, linking population dynamics processes at local and regional scales to processes at the ecosystem level, thus reflecting a macroecological perspective of marine pelagic systems.