Detection of delayed density dependence in an orchid population

Abstract

1. Annual censuses of Orchis morio (green-winged orchid) flowering spikes have been taken over a 27-year period in a replicated factorial experiment on the effects of fertilizer application. Census data, combined by block or treatment, were used in time-series analyses to test for density dependence. 2. Partial autocorrelation functions revealed the importance of positive correlations at lag 1 and negative correlations at lag 5. Stepwise multiple regressions provided evidence of delayed density dependence, again with a delay of about 5 years, with no evidence of direct (first-order) density dependence. 3. First-order autocorrelations and delayed density dependence were considered in the light of the known stage structure and generation time of the plant and the possibility of density dependence at different points in the life history. 4. Model structure affects the detection of density dependence, increasing the propensity for type I errors.