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A STOCHASTIC MICROSCOPIC MODEL FOR POPULATION DYNAMICS

Pest control is a basic problem in agriculture. Recentely, research on sustainable pest control strategies has become very important. Implementation of biological and integrated control strategies is based both on the knowledge of pest population abundance and the possibility to forecast the time evolution of the population dynamics in order to optimize the control operations.
Jointly with ENEA - La Spezia and the University of Reggio Calabria, a modelling strategy for a single species population dynamics of insects or acari is proposed, based on a mathematical microscopic model describing, via stochastic differential equations, the life history of an individual of a structured population. The history is determined by the biological processes of development, reproduction and mortality and the status of an individual is individuated by its stage and its physiological age in the stage. The latter is defined by the percentage of development in the stage for non reproductive individuals, and by the percentage of the potential reproductive effort realized for an adult female. The dynamics of the overall population is determined by the time evolution of the status of all its individuals.
The main objective is to produce a detailed description of the time evolution of the physiological age distribution of individuals and of the population abundance, taking into account the effects of biological and environmental variability on the fundamental life history parameters.
The model has been applied to the case of Trialeurodes vaporariorum, a phytophagous of tomato culture in greenhouse. The simulation has been made under the assumption of constant temperature. Time evolution of the population has been studied for a long period (fig. 1) in order to obtain asymptotic behavior of some parameters (intrinsic growth rate, population stage structure).
The initial phase of a phytophagous population dynamics is the most important period for biological control. Thus the model has been applied to simulate the initial growth of a population starting from observed initial conditions: the good agreement with experimental results confirms that the model approximate quite well the demographic evolution of the population (fig. 2).
The same microscopic model will be applied to zooplankton, making use of experimental and field data relative to a calanoid copepod species that is very abundant in Mediterranean coastal waters. Population dynamics will be simulated under different food conditions to test the effect of the diet on population development. The results will be compared with data recorded in the field at a fixed station in the Gulf of Naples. This study is included in a research project conducted by the Stazione Zoologica di Napoli and focused on the long-term dynamics of neritic zooplankton.

CNR IMATI - Sezione di Milano

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