COMMENT ARISING FROM A PAPER BY WOLDA AND DENNIS - USING AND INTERPRETING THE RESULTS OF TESTS FOR DENSITY-DEPENDENCE

We argue that tests for density dependence are useful in analyses of p opulation dynamics and suggest guide lines for their use and interpret ation of results which avoid many of the problems discussed by Wolda a nd Dennis (1993). Processes other than density dependence per se can c ause statistical tests to indicate the presence of density dependence (Wolda and Dennis 1993 and unpublished simulations). Tests for density dependence cannot reveal the mechanism of regulation, but they do ind icate the nature of long-term population dynamics. Tests for density d ependence give misleading results if sampling is not at generation int ervals; however, this problem is avoided if we only use tests on data collected in each generation (Holyoak 1993a). Similarly, species shoul d be semelparous. Non-delayed density dependence should not be conside red without looking for delayed density dependence, since the presence of delayed density dependence can lead to over-detection of non-delay ed density dependence (Woiwod and Hanski 1992; Holyoak 1993b). The par tial autocorrelation function and knowledge of life-history are more u seful than tests for density dependence for indicating whether any den sity dependence is delayed or not (Royama 1992; Holyoak 1993b). Estima tion error with a constant upper size limit causes tests for density d ependence to overestimate the frequency of delayed density dependence; however we do not know whether estimation error is bounded in real po pulations. Work in progress suggests that 20-40 generations (depending on the nature of population dynamics) gives a moderate level of accur acy with tests for density dependence, and > 40 generations are necess ary for tests to be accurate in their assessment of the strength of de nsity dependence. We conclude that tests are useful indicators of whet her density dependence, or other feedback mechanisms are likely to be acting.