Niche overlap of parasitoids in host-parasitoid systems: its consequence to single versus multiple introduction controversy in biological control.
The importance of niche overlap between parasitoids in the single- or multiple-introduction problem in biological control is exhibited by mathematical analysis of one host-two parasitoid systems. Models of host-parasitoid systems are briefly reviewed, and it is clarified that the one host-two parasitoid models so far presented cover only a special case with respect to niche overlap between parasitoids, and that this is the reason multiple introduction has been supported. Spatial heterogeneity of the host habitat is treated as heterogenous likelihood of hosts being attacked by parasitoids. This idea provides a basis for considering niche overlap of parasitoids. The negative polynomial model is proposed to model the case where 2 parasitoid species show aggregative response (the niches of the 2 parasitoids overlapping completely). The analysis concludes that single introduction is always superior. Another new model that can cover various situations of niche overlap is proposed to show that single introduction is much superior if the niches of 2 parasitoids overlap to a large extent. A graphical method is proposed to determine the superior strategy (single or multiple introduction).