Influences of Resource Patch Distribution on a Host-Parasitoid System Stability in Patchy Environment: A Laboratory Study

Abstract

Influences of the spatial distribution of resource patches on the host-parasitoid system (brown rice patch - rice weevil - Anisopteromalus calandrae) dynamics and stability in patchy environment were studied with a biological model system. When the 40 resource patches (each containing 5 g of brown rice) were contagiously distributed among 453 empty patches, the host population increased logistically and then fluctuated at an equilibrium level about 5,000. However, when the resource patches were randomly distributed, the host population showed a cyclical fluctuations in the range from 532 to 7089 with significant delayed density-dependence. Distribution of resource patches affected the distribution of hosts among resource patches, which could be a reason for the different features of population dynamics in the two system. In both resource patch distribution systems, the interactions between host and parasitoid populations could be persistent and maintained at an equilibrium level with oscillatory damping. The equilibrium level in each system was far below than that in the system without parasitoid, suggesting that the parasitoid did regulate the host population. However, overall mortality of host due to the parasitism was host density-independent in the contagious system or inversely host density-dependent in the random system. Therefore, the regulation seemed due not to overall host density-dependent parasitism, but rather to the indirect effect of the parasitoid leading the host population to be highly aggregating to some resource patches, which, in turn, resulted in stronger intraspecific competition. The key factor in regulation of the host population was estimated to be intraspecific competition in the contagious resource patch system, whereas it was parasitism in the random patch system. The persistence and stability of host-parasitoid population interaction, the role of parasitoid in the interaction and the resulting equilibrium level were discussed with reference to the resource patch distribution.