Demography of the Marine Bivalve Yoldia notabilis in Fluctuating Environments: An Analysis Using a Stochastic Matrix Model

Abstract

A population of the marine bivalve Yoldia notabilis in Otsuchi Bay, northeastern Japan shows large interannual fluctuations in recruitment rate and individual growth rate. The effects of these fluctuations on population growth rate were examined using a stochastic size-classified matrix model. Stochastic population growth rate (In Xs) estimated by numerical iterations differed greatly between models with lognormal distributions and normal distributions fitted to the fluctuating recruitment rate. The estimates of In Xs, its confidence interval and In g (growth rate of average population size) increased greatly with an arbitrary increase in the variance of recruitment rate, while the variance in individual growth rate has less effects on the estimates of these parameters. The fluctuation in recruitment has therefore more impact on the population dynamics. The stochastic growth rate In Xs was always no greater than In I, the latter equivalent to the deterministic growth rate, and their difference increased with the variance in the recruitment rate and the individual growth rate, suggesting that the population growth rate estimate based on average vital rates may be an overestimate. These findings demonstrate that the estimates of population growth rates are greatly influenced by the types of probability distributions fitted to fluctuat