Simulations of the predator-prey interactions in a two species ecotoxicological test system

A mathematical simulation model (Gutierrez type) has been developed to investigate the predator-prey interactions in a two species ecotoxicological test system. The test system consists of the predacious mite ( Hypoaspis aculeifer Canestrini) and, as prey, the collembolan Folsomia fimetaria L. in a microcosm (5.5 cm high × 6.0 cm in diameter) with 30 g humidified soil. F. fimetaria is provided with bakers yeast as food source. The model simulates (i) the population development of the test animals in synchronous cultures before the test, (ii) the selection of the test animals from the synchronous cultures and (iii) predator-prey interactions with and without the presence of dimethoate during the test and extraction periods. The driving variable is the temperature dependent food demands of the organisms. Both species were simulated with separate male and female populations, which were divided into a number of life stages. Thus the model handles very complicated predator-prey interactions taking the different interactions between different instars into consideration. The simulated test results were found to be very sensitive to changes in predator search rate, capture efficiency, habitat overlap, the amount of stored reserves of H. aculeifer at test start and the survival and reproduction of F. fimetaria. The simulations constitute the foundation for suggestions for further improvement of the test system.