A physiologically-based tritrophic metapopulation model of the African cassava food web

The metapopulation dynamics of the African cassava food web is explored usi ng a physiologically based tritrophic model. The interacting species are ca ssava, cassava mealybug and its natural enemies (two parasitoids, a coccine llid predator and a fungal pathogen), and the cassava greenmite and its nat ural enemies (two predators and a fungal pathogen). The metapopulation mode l is based on a single patch age-structured population dynamics model repor ted by Gutierrez et al. (Gutierrez, A.P., Wermelinger, B., Schulthess, F., Baumgartner, J.U., Herren, H.R., Ellis, C.K., Yaninek, J.S., 1988b. Analysi s of biological control of cassava pests in Africa: I. Simulation of carbon nitrogen and water dynamics in cassava. J. Appl. Ecol. 25, 901-920; Gutier rez, A.P., Neuenschwander, P. van Alphen, J.J.M., 1993. Factors affecting t he establishment of natural enemies: biological control of the cassava meal ybug in West Africa by introduced parasitoids. J. Appl. Ecol. 30, 706-721). The same model simulates the mass number dynamics of each plant or animal species in each patch and the movement of animals between patches. Movement is based on species specific supply-demand relations. The pathogen mortali ty rate is a simple function of rainfall intensity. The within-patch specie s composition, their initial densities, and the initial values of edaphic v ariables may be assigned stochastically. Sensitivity, graphical and multipl e linear regression analyses are used to summarize the effects of spatial a nd resource heterogeneity on species dynamics. Important plant level effect s on higher trophic levels are demonstrated, and recommendations are made a s to the appropriate model for different ecological studies. (C) 1999 Elsev ier Science B.V. All rights reserved.