A TEST OF HETEROGENEOUS MIXING AS A MECHANISM FOR ECOLOGICAL PERSISTENCE IN A DISTURBED ENVIRONMENT

Persistence is a central issue in population ecology with important im plications for population management. Most theoretical studies have fo cused on continually interacting populations, even though many systems are subject to ecological disturbances which confound analysis of per sistence. In this paper, we use a combination of a simple parasite-hyp erparasite model with disturbances and field data to investigate the f actors contributing to the observed persistence of the parasite popula tion. The field data are taken from a two-year experiment (including f ive growing seasons) investigating the use of the mycoparasite Sporide smium sclerotivorum as a persistent biological control agent of Sclero tinia minor, an economically important fungal parasite of lettuce. We show that the standard assumption of homogeneous mixing fails to predi ct the observed persistence of the parasite population. We demonstrate that allowing for heterogeneous mixing prevents the fade-out predicte d in the homogeneous mixing case. The implications of the results for broad classes of host-parasite systems are discussed.