Document: OTT-3-92-10

Stochastic age-structured dynamics: Cycles and trends.

BJORNSTAD, O.N.*

University of California Santa Barbara, Santa Barbara, CA 93101 USA ¹

Abstract:
Many marine fish exhibit competitive and cannibalistic interactions that are age-structured. In addition, large variability in per capita reproductive rates is often observed. Stochastic recruitment and age-structured interactions are also a common trait in many terrestrial ungulates. We investigated the consequences of environmental stochasticity in reproduction on the dynamics of age-structured populations. We showed how environmental stochasticity may be echoed by density-dependent processes to induce low frequency dynamics. These low frequency signals may appear as trends, orders of magnitude longer than the characteristic time (generation time) of the process. We utilized Fourier analyses to establish a causal link between the inter-cohort interactions and the long-term trends. The 'trends' arose from the interplay between stochastic vital rates and interchort interactions. Theoretical explorations of different life cycles indicate that trends may commonly arise or be enhanced in age-structured populations with stochastic reproduction. The current study elucidates a less-explored way in which density-dependent and stochastic factors interact in ecologically realistic population models to induce long-term trends.

Keywords: Age-structured dynamics, Fish dynamics, Nonlinear Stochastic Dynamics, Stock recruitment, Time series, Transfer function

This abstract is being presented at: 10:30 AM in session:
STATISTICAL ECOLOGY