Combining different forms of parasitoid aggregation: effects on stability and patterns of parasitism

Two models blend different forms of parasitoid search behavior; aggregation independent of host density, and in response to host density. In Model A parasitoid and host densities on a patch are assumed to be positively correlated, while in Model B the parasitoids have a linear regression on host density, with an associated error term. In Model A, the dynamics were least stable when host and parasitoid were perfectly correlated. In Model B, the slope of the regression had only a moderate effect on stability, while large amounts of error strongly promoted stability. Results suggest that a weak and noisy aggregative response by the parasitoid may be strongly stabilizing, while a strong relationship between parasitoid and host density can sometimes produce instability. As a strong relationship also produces spatial density-dependence in parasitism rates, such a pattern in the field need not indicate stabilizing forms of parasitoid behavior. -Authors