A new application of principal response curves for summarizing abrupt and cyclic shifts of communities over space

Abstract

There is a growing need to easily describe and synthesize the dynamics of ecosystems' components in space and time. Most multivariate analyses provide ordination diagrams or biplots that are too cluttered to allow simple reading and are unfamiliar to most users. To overcome such difficulties, a novel application of principal response curves (PRCs) is proposed. Principal response curves are traditionally used to assess treatment effects on community structure measured repeatedly over time. In this new application, the tested factor and the repeated-observation axis are replaced by time and space, respectively. The georeferencing of sampling sites permits to produce an easy-to-read map that summarizes both the temporal dynamics of the community and the contribution of each species to these dynamics at each sampling site. A 24-yr-long time series of scientific surveys monitoring 77 fish and cephalopod species in the Eastern English Channel is used to illustrate the novel application of the PRC method. This new application could prove a relevant tool for the ecosystem approach to human activities management by providing spatialized indicators of community changes, as spatial monitoring tools are increasingly recommended for measuring the effectiveness of management actions.