Principal response curves: Analysis of time-dependent multivariate responses of biological community to stress

In this paper a novel multivariate method is proposed for the analysis of c ommunity response data from designed experiments repeatedly sampled in time . The long-term effects of the insecticide chlorpyrifos on the invertebrate community and the dissolved oxygen (DO)-pH-alkalinity-conductivity syndrom e, in outdoor experimental ditches, are used as example data. The new metho d, which we have named the principal response curve method (PRC), is based on redundancy analysis (RDA), adjusted for overall changes in community res ponse over time, as observed in control test systems. This allows the metho d to focus on the time-dependent treatment effects. The principal component is plotted against time, yielding a principal response curve of the commun ity for each treatment. The PRC method distills the complexity of time-depe ndent, community-level effects of pollutants into a graphic form that can b e appreciated more readily than the results of other currently available mu ltivariate techniques. The PRC method also enables a quantitative interpret ation of effects towards the species level.