RECONCILING CLASSICAL AND INDIVIDUAL-BASED APPROACHES IN THEORETICAL POPULATION ECOLOGY - A PROTOCOL FOR EXTRACTING POPULATION PARAMETERS FROM INDIVIDUAL-BASED MODELS

The two main approaches in theoretical population ecology-the classica l approach using differential equations and the approach using individ ual-based modeling-seem to be incompatible. Linked to these two approa ches are two different timescales: population dynamics and behavior or physiology. Thus, the question of the relationship between classical and individual-based approaches is related to the question of the mutu al relationship between processes on the population and the behavioral timescales. We present a simple protocol that allows the two differen t approaches to be reconciled by making explicit use of the fact that processes operating on two different timescales can be treated separat ely. Using an individual-based model of nomadic birds as an example, w e extract the population growth rate by deactivating all demographic p rocesses-in other words, the individuals behave but do not age, die, o r reproduce. The growth rate closely matches the logistic growth rate for a wide range of parameters. The implications of this result and th e conditions for applying the protocol to other individual-based model s are discussed. Since in physics the technique of separating timescal es is linked to some concepts of self-organization, we believe that th e protocol will also help to develop concepts of self-organization in ecology.