BRS: Peter Chesson "Aedt: the new equilibrium for the nonequilibrium world of an ever-changing climate"

host: Elizabeth Wolkovich, cookies Ellen N and Carla DF

Abstract:

The concept of equilibrium has always been controversial but always central in ecological thought. The problem is that most natural populations fluctuate greatly, and may exhibit trends on observable time scales. In the past, there have been various replacements for the equilibrium concept, but 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. A new concept, an asymptotic environmentally-determined trajectory (aedt) is 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 reflects interactions between organisms and their changing environment, and invokes the kinds of questions and predictions long familiar to ecologists but in a much more realistic context. Unlike the traditional equilibrium and many of its proposed replacements, population densities are predicted to closely follow the AEDT because environmental fluctuations are accounted for fully in its calculation. Realistic consideration of environmental history and a future changing profoundly due to human influence becomes possible.

The aedt concept extends to consideration of the environment that a population actually experiences as it moves around a complex landscape subject to global climate change. Although the environment at any one locality may show strong temporal trends, the environment experienced by a population need not have any strong trends. However, the experienced environment under long-term temporal change will generally differ by being less favorable on average than without long-term temporal change. These results suggest theoretical and empirical research programs on the characteristics of landscapes, dispersal and temporal change affecting the properties of experienced environments. They imply moving away from local population and community thinking to conceptualization and study of populations and communities on multiple spatial and temporal scales. Many standard ecological methods and concepts may still apply to populations tracked as they move on a landscape, while at the same time, understanding is enriched by accounting for how dispersal processes and landscape complexity, interacting with temporal change, affect those moving populations.