A MECHANISTIC SIMULATION TO COMPLEMENT AN EMPIRICAL TRANSITION MATRIX MODEL OF ACARINE POPULATION-DYNAMICS

Ecological modeling has a diversity of aims which can be summarized under three main objectives: realism, precision and generality. We designed a simulation model of a three-species acarine system, containing a phytophagous tetranychidae mite, Panonychus ulmi Koch, and two predators: a phytoseiid (Typhlodromus caudiglans Schuster) and a stigmaeid (Zetzellia mali Ewing) to attempt to complement the extreme precision of an empirical transition matrix model of the same system of Woolhouse and Harmsen (1987), with biological realism. As Woolhouse and Harmsen speculated, but were unable to show using their empirical model, our simulation model demonstrated that age structure, availability of prey and abundance of predators are important determinants of the dynamics of the acarine system. More specifically, our model provided evidence that age structure and life history (particularly that of P. ulmi), the overall functional response of predators, the high preference of stigmaeids for P. ulmi eggs and other stigmaeid characteristics such as cannibalism all strongly influence predator-prey and predator-predator interactions. Both model types are useful for management purposes: the empirical or statistical approach produces accurate predictions, but cannot provide managers with information on how to manipulate the biology of the system to produce favorable conditions for control; the mechanistic or reductionist approach provides information on how complex biological interactions affect overall population dynamics, but cannot provide the same degree of precision as the empirical approach. We suggest that using two or more modeling approaches to the same problem, each seeking to maximize one of the three recognized aims in ecological modeling (i.e. realism, precision and generality), may be an efficient method for achieving a more complete understanding of ecological systems.