Abstract
A mathematical model of copepod population dynamics coupling individual growth and development was tested. The results show in detail the effect of applying various hypotheses, particularly concerning the relationship between certain physiological processes (ingestion, egestion, excretion, oogenesis, etc.) and processes controlling the time course of abundance of individuals in each instar (mortality rate, moulting rate, reproduction). The model shows the changes in physiological processes (~ngestion, growth rate, etc.) at the individual level as a function of age within stage, and consequently the probability of moulting and death. If an indiv~dual remains for some time at one stage, its growth rate decreases, weight does not increase, the abil~ty to moult is lost and the probability of death is greater. In addition, the model glves the mean values of processes for the whole population, as could be obtained expenmentally, but it also provides an explanation of the variability of processes related to the population age structure. Finally, the results of this mathematical model led to an experimental test of the validity of the hypotheses put forward. The mathematical model can be used in all conditions, since it simulates values of processes constant in time as long as the external conditions are also constant, while remaining capable of expressing the internal dynamics of a population when the environment is suddenly perturbed.
Highlights
For a better understanding of the dynamics of a planktonic population w i t h the pelagic ecosystem, 2 types of processes should be considered: demographic and biogeochemical
In models of larval dynamics, development and mortality rates generally are linked directly to external parameters by empirical relationships, which do not take into account the energetic processes involved in dynamics (Davis 1984,Sciandra 1986).these external parameters affect the physiology of organisms in several ways, either ensuring normal development or inducing developmental difficulties, even death
O Inter-Research 1992 physiological steps act as filters for certain variations of external parameters, which are subject to strong fluctuations in the pelagic environment, and contribute to time lags observed in population dynamics
Summary
For a better understanding of the dynamics of a planktonic population w i t h the pelagic ecosystem, 2 types of processes should be considered: demographic (flux of animals) and biogeochemical (cycles of matter). These 2 approaches are quite often modelled separately (Cale 1988)for 2 reasons. A conceptual scheme has been proposed in the model established by Carlotti & Sciandra (1989) and Carlotti (1990), which integrates biomass and demographic criteria simultaneously In this model, the processes involved in individual growth
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