Population dynamics of two marine polychaetes: The relative role of density dependence, predation, and winter conditions

Abstract

We modelled the population dynamics of two polychaete species, a prey (Scoloplos armiger) and its predator (Nephtys hombergii) by simple linear and non-linear time-series models using a 29 year data series of population abundance and winter conditions. The log reproductive rate (i.e., the difference in log density between two succeeding years) of the prey population was density dependent and negatively related to the density of the predator. The log reproductive rate of the predator was also density dependent, but was to a greater extent determined by winter temperature, a density-independent factor. Log reproductive rate of the predator was not related to the density of the prey, nor could delayed density dependence be detected. Apparently, the feedback mechanism between predator and prey was weak, perhaps because the predator is a generalist. Predator density can therefore be categorized as a density-independent factor with respect to the dynamics of the prey species. In neither of the two species was density dependence strong enough to generate complex or chaotic behaviour, as indicated by the weakly negative slope of the reproduction curve at the equilibrium, the apparent lack of a non-linear component in the reproduction curve, and the negative Lyapunov exponent. © 2000 International Council for the Exploration of the Sea.