Aedt: A new concept for ecological dynamics in the ever-changing world
The concept of equilibrium has always been controversial and has always been central in ecological thought. It has been the basis of prediction in ecology, as in many sciences. The vicinity of equilibrium commonly defines the properties expected of a system. In conservation, equilibrium, as a formalization of the ancient concept of the balance of nature, has been imagined to define the essence of a system and to be treated with reverence. However, most natural populations fluctuate greatly, and may exhibit trends on observable time scales. Limit cycles, strange attractors, and stationary probability distributions are various replacements for the equilibrium concept, but they all suffer from the complaint that they are merely equilibria on different scales. None account for long-term climate fluctuations, which are nonstationary and preclude these alternative concepts because they all imply stable long-term frequencies of population states.
I demonstrate a new concept, asymptotic environmentally-determined trajectories (aedts), able to replace the traditional equilibrium concept while retaining much of its predictive power even though the environment is realistically nonstationary incorporating the fact that the physical environment, including climate, changes on all time scales without stable repetition frequencies. An aedt is a function of time and is determined by the time series of environmental states and the dynamical rules for the system but is independent of initial population sizes. It thus reflects the multiplicities of interactions between organisms and with their environment. It invokes the kinds of questions and predictions long familiar to ecologists but in a much more realistic context. Convergence of system dynamics on an aedt involves consideration of feedback loops and stability properties that are generalizations of much traditional theoretical ecology while not requiring the usual stationarity assumption. Realistic consideration of environmental history and a future changing profoundly due to human influence becomes possible.