Measuring the functional redundancy of biological communities: a quantitative guide

The preservation of ecosystem processes under ongoing biotic erosion requires that some species within affected communities perform similar functions, a property that is usually defined as functional redundancy. Although functional redundancy has recently become a relevant part of ecological research, so far there is no agreement on its measurement. The scope of this work is thus to propose a consistent framework based on functional dissimilarities among species for summarizing different facets of functional redundancy. The behaviour of the proposed measures is illustrated with one small artificial data set, together with actual examples on the species functional turnover along successional gradients. We believe this new framework provides an important contribution for the clarification and quantification of key metrics of community redundancy and vulnerability. The method, for which we provide a simple r function called uniqueness', further allows summarizing the functional contribution of single species to the overall redundancy of any type of biological community.