Stage-structured models

Abstract

This chapter moves to models in which developmental stage is the individual state variable, and abundance at each stage is the population variable. Stage is a period within an individual life history (e.g. juvenile, adult); organisms may survive within a stage or “grow” to other stages. This movement and survival is represented by a projection matrix that describes the transitions between stages over time. The projection matrix is similar to the Leslie matrix for age-structured models (Chapter 3), except it has entries other than just those in the first row and the sub-diagonal. Stage models are conceptually problematic because real population dynamics ultimately depend on the age distribution within each stage category. Stage-based models obscure that age structure, thus stage is not an adequate expression of state (Chapter 1). This chapter demonstrates how this introduces artifacts in model analysis, particularly of transients, and presents some ways to avoid those artifacts.