DENSITY-DEPENDENCE AND AGE STRUCTURE - NONLINEAR DYNAMICS AND POPULATION BEHAVIOR

We characterize the dynamics of age-structured density-dependent popul ations with yearly reproduction. In contrast to prior studies focusing primarily on behavior near the stability boundary, we describe the dy namics over the full range of linear and nonlinear behavior. We descri be model dynamics in terms that have direct biological interpretations . We illustrate the use of our approach by examining the dynamics of D ungeness crab (Cancer magister) in detail. Model dynamics are found to be very sensitive to changes in life-history parameters. Small change s in vital rates can cause population density to suddenly jump from lo w to high variability or vice versa. Nonmonotonic switching between ch aotic and nonchaotic dynamics is also observed. The period (or dominan t timescale) of cyclic behavior is loosely related to values of vital rates, typically increasing with adult survivorship, but can remain co nstant while vital rates change. Model dynamics are also found to be s ensitive to environmental perturbations. For example, model dynamics m ay be chaotic or nonchaotic for fixed parameter values with environmen tal perturbations switching model dynamics between these distinct beha viors (i.e., the dynamics are nonstationary). These findings illustrat e one possible explanation for the variety of dynamic behavior in Dung eness crab populations (and other natural populations) and temporal (O r spatial) shifts in behavior.