A new method for quantifying the phylogenetic redundancy of biological communities

The increasing use of phylogenetic methods in community ecology recognizes that accumulated evolutionary differences among species mirror, to some extent, ecological processes. The scope of this work is thus to propose a new method for the measurement of community-level phylogenetic redundancy, which takes into account the branching pattern of the underlying phylogeny. Like for functional redundancy, a measure of phylogenetic redundancy can be described as a normalized measure in the range (0-1) that relates the observed community-level phylogenetic diversity to the value of a hypothetical assemblage with the same abundance distribution of the focal community in which all species had independent evolution. Therefore, phylogenetic redundancy can be interpreted as the diversity decrease that is obtained by taking into account the evolutionary relationships among species in the calculation of diversity. The behavior of the proposed method, for which we provide a simple R function called 'phyloredundancy', was evaluated with published data on Alpine plant communities along a primary succession on a glacier foreland in northern Italy. As shown by our results, the method accounts for the length of shared branches in the phylogeny, producing a coherent framework for describing the evolutionary relationships within a species assemblage. Being based on classical diversity measures, which have been used in ecology for decades, it also has a great potential for future research in phylogenetic community ecology.