Process Models, Equilibrium Structures, and Population Dynamics: On the Formulation and Testing of Realistic Theory in Ecology

This paper addresses problems in the formulation and testing of theory to relate structure and dynamic behaviour in complex natural ecosystems. Detailed studies of spruce budworm-coniferous forest interactions in eastern Canada provide a background for the analysis. We argue that the mixed spatial and temporal scales, low density phenomena, and nonlinear interactions characteristic of most ecosystems severely limit traditional statistical approaches to theory building, while rendering most kinds of observational data irrelevant to theory evaluation and testing. We describe an alternative tradition: 1. Cast the theory as a set of "dynamic life tables", bound together by basic ecological process modules; apply available data and field experience to the parameterization of these modules. 2. Compute the consequences of the resulting theory under a wide range of conditions: quantitatively through numerical simulation and qualitatively through the use of topological manifolds. 3. Employ the manifolds to identify key structure- (as opposed to parameter-) dependent predictions of the theory. Compare these with observation, emphasizing behaviour of the system and its theory in extreme natural or experimental situations