Showing papers by "Michael P. Hassell published in 1992"

The spatial dynamics of host-parasitoid systems

Abstract: We consider models for host-parasitoid interactions in spatially patchy environments, where in each generation specified fractions of the host and parasitoid subpopulations in each patch move to adjacent patches. In most previous work of this general kind, the movement is not localized in this way, but involves «global» mixing of the populations prior to dispersal. A remarkable range of dynamical behaviour is exhibited by a mathematically explicit model with constant host reproductive rate, deterministically unstable local dynamics and dispersing hosts and parasitoids that only move to nearest-neighbour patches in a density-independent way

Heterogeneity and density dependence in a field study of a tephritid-parasitoid interaction

Abstract: . 1 The spatial distributions of two tephritid flies (Urophora stylata (Fabricius) and Terellia serratulae L.) attacking thistle flower heads and the levels of parasitism from their associated parasitoid guilds were studied over a 7-year period. 2 Using these data it is possible to seek both temporal, density dependent relationships between average levels of parasitism and host density per generation, and also any spatial patterns of parasitism contributing to stability that may be operating within the same field system. 3 Parasitism by the two most important generalist parasitoids of T.serratulae is a direct function of average T.serratulae density per year. There is little evidence of any stabilizing heterogeneity arising from the spatial distribution of parasitism within generations. 4 Temporal density dependence of Urophora stylata cannot be confirmed from the 7 years of study but there is evidence of spatial heterogeneity which may have an important effect on the dynamics of the host population.