Aggregation of Parasitoids and the Detection of Density Dependence in Field Populations

of their models. Field experimental tests are not without problems, particularly where indirect effects of other interacting species may confound interpretations (Connell 1983, Quinn and Dunham 1983, Bender et al. 1984). Careful experimental designs, together with monitoring of changes in associated species that could produce indirect effects, probably remains the best way to test theories of succession. Walker and Chapin (1987) suggest that "it may be premature to synthesize our understanding of succession into a unified theory". However any synthesis of current knowledge into a theory could usually be judged premature, since knowledge is always incomplete. The models proposed by Walker and Chapin (1987: Fig. 1), like those of Connell and Slatyer (1977) are based upon incomplete knowledge, but are welcome because they stimulate thought and indicate directions for further investigation.