Aggregation of risk: relationships among host- parasitoid models.

Models in which parasitoid density in a patch is strictly a function of host density in the patch, with no 'error' about this function, are pure-regression models. Those in which there is random variation in the number of parasitoids per patch, with no relationship between local parasitoid density and local host density, are pure-error models. The key factor in these models is not the distribution of parasitoids per se, but the distribution of the relative risk of parasitism which in the present formulation can result from variation in the number of parasitoids in a patch or from variation in host vulnerability. -from Authors