Population dynamics of apparent competition in a host-parasitoid assemblage

The population dynamics of two moth species, Plodia interpunctella (Hübner) and Ephestia kuehniella Zeller in the presence of their shared parasitoid, Venturia canescens (Gravenhorst), were studied in well replicated time series experiments. Moths were prevented from competing for resources and could therefore only interact via the shared parasitoid. This study examines the consequences of apparent competition on the population dynamics of a simple laboratory insect assemblage. Ephestia kuehniella suffers severly in the presence of the shared parasitoid. In all eight replicates, this moth species is eliminated. Time series analysis reveals that the E. kuehniella populations show divergent oscillations. Plodia interpunctella and V. canescens populations show persistent populations. Time series analysis reveals that there is a delayed density dependence acting on these populations and the dynamics are either stable equilibrium or damped oscillations. Repeated-measures analysis of the strength of the indirect interaction reveals that the effects of apparent competition before E. kuehniella is lost are amensal. The indirect interaction between E. kuehniella and P. interpunctella is [-, 0] rather than [-, -].