Testing for differences in beta diversity from plot-to-plot dissimilarities

The central role of beta diversity in describing biodiversity patterns has been investigated in many fields of ecology and biogeography. While a variety of measures of beta diversity have been proposed over the past five decades, the question of how to test for differences in beta diversity among different sets of sampling plots has been addressed only rarely. Here, we describe a simple analytical procedure to test for differences in beta diversity among distinct sets of plots. The advantage of this approach compared to methods that have been previously proposed lies in its randomization procedure. Such a procedure creates a distribution of null values of the test statistic that is compatible with the null hypothesis of no significant difference in multivariate dispersion between the groups. The proposed test was illustrated using a large dataset of plant and water beetle (Coleoptera) assemblages collected from 45 farmland ponds in Ireland.