Life history and population dynamics of Metridia pacifica: Results from simulation modelling

Abstract

A numerical population dynamics model (POPCYCLE) has been developed that predicts numbers and phenology of the copepod Metridia pacifica Brodsky, and which was used to investigate the functional response parameters of this copepod. To accomplish these modelling goals, we developed an ‘individual vector model’. This mode of modelling is powerful, in that physiological functions are represented at the individual level (the level at which they operate), and flexible, in that extensions and applications are straightforward to implement since the fundamental unit within the model is the individual. Inter-individual variation in physiology is easily represented and the results of such variation are explicit in the model output. Equations describing growth, mortality, and reproduction are formulated and used to describe the development of individuals and to generate a population dynamics history for year-long model runs. Growth is described using an energetics-based, input-output model. Mortality is implemented as a constant daily probability of predation. Reproductive parameters of clutch size, clutch frequency, and total number of clutches are chosen to provide lifetime egg production similar to those previously reported for other calanoid copepods. In formulating the model, it was assumed that growth of M. pacifica in the subarctic Pacific was food-limited, and that temperature was unimportant. Seasonal abundance and life history data for M. pacifica from Station P in the subarctic Pacific were used to evaluate the validity of the model. The timing of life processes, such as the time for development from egg to egg, was considered the important criterion for judging the suitability of the model and chosen functional response parameters. A criterion of secondary importance was stage densities in the model similar to those observed in the field. ‘Reasonable’ parameter sets provided growth rates which allowed completion of development in a generation time of approximately 100 days; the generation time observed in the field.