Fish Cohort Dynamics: Application of Complementary Modeling Approaches

Abstract

Abstract.The recruitment to the adult stock of a fish population is a function of both environmental conditions and the dynamics of juvenile fish cohorts. These dynamics can be quite complicated and involve the size structure of the cohort. Two types of models, i-state distribution models (e.g., partial differential equations) and i-state configuration models (computer simulation models following many individuals simultaneously), have been developed to study this type of question. However, these two model types have not to our knowledge previously been compared in detail. Analytical solutions are obtained for three partial differential equation models of early life-history fish cohorts. Equivalent individual-by-individual computer simulation models are also used. These two approaches can produce similar results, which suggests that one may be able to use the approaches interchangeably under many circumstances. Simple uncorrected stochasticity in daily growth is added to the individual-by-individual models, and it is shown that this produces no significant difference from purely deterministic situations. However, when the stochasticity was temporally correlated such that a fish growing faster than the mean 1 d has a tendency to grow faster than the mean the next day, there can be great differences in the outcomes of the simulations.The great majority of models of ecological populations describe populations as homogeneous collections of organisms. However, to an increasing degree, ecologists have become aware that the internal age and size structures of populations can have a decisive influence on the population dynamics (Ebenman and Persson 1988). Size structure may be particularly important in populations in which growth is fairly plastic and feeding and vulnerability to predation depend on size. The first factor, plasticity in growth, leads to the potential for a wide spectrum of organism sizes in the population, even within cohorts of individuals of the same age. The second factor, size dependence of feeding and vulnerability, means that members of an age-class cohort that have different sizes will have different probabilities of success in surviving and reproducing.These factors affect the dynamics of a population cohort and thus have many ramifications, both theoretical and practical, in ecology. On the theoretical side, there are questions of appropriate parental strategies (e.g., size of eggs, early parental care) and individual growth strategies in the face of environments with various size-dependent food availabilities and risks of predation. On the practical side, the recruitment of juvenile fish to the adult classes in commercial fish species is extremely important but is not well understood. It is quite possible

Local Foraging and Limited Mobility: Dynamics of a Size-Structured Consumer Population

“…Eventually this culminates in a high number of adults in the population, which produce a large pulse of offspring that temporarily dominates the resource and thus population dynamics. DeAngelis et al (1993) study the influence of stochasticity in growth rates of individuals on the dynamics of a fish cohort. They show that stochastic perturbation of these rates over time per se has no significant effect on the developing size distribution of the cohort.…”

“…In our current work, we assume a positive relation between attack rate and size for the entire juvenile size range. Hence, in this respect, our model corresponds to that of DeAngelis et al (1993); when food is not limiting, larger individuals grow faster than smaller individuals. However, we consider the complete population dynamical feedback loop, including the resource dynamics.…”

Estimating von Bertalanffy parameters with individual and environmental variations in growth

“…A common and important occurrence of individual variation is in the context of somatic growth [15,50,51]. Individual variation in growth can arise from a variety of processes.…”

Population growth of northern anchovy and Pacific sardine using stage-specific matrix models

“…Also, field research is required to refine and determine the covariance of vital rates. For example, rapid growth in one stage may confer growth rate advantages in subsequent stages, hasten the onset of maturity and provide additional advantages for evading sources of mortality a s indicated by DeAngelis et al (1993) from their individualbased models. The covariance is also essential for analytical computation of variance of h estimates.…”