Relationships between taxonomic resolution and spatial scales of multivariate variation

1. We investigated the effects of changes in taxonomic resolution on analyses of patterns of multivariate variation at different spatial scales for the highly diverse fauna inhabiting holdfasts of the kelp Ecklonia radiata. 2. Multivariate analyses were performed using several transformations to examine differences in spatial patterns of variation from metres up to hundreds of kilometres for composition vs. relative abundance in assemblages. 3. The greatest variability in assemblages occurred at the smallest spatial scale, from plant to plant, pointing to the existence of important small-scale processes. The proportional amount of variation at the smallest spatial scale decreased with decreasing taxonomic resolution (i.e. from species through to phyla). For composition, the next-greatest source of variation was at the largest spatial scale (hundreds of kilometres), while for relative abundance, the next-greatest source of variation was at the level of sites (hundreds of metres to kilometres). 4 For abundance data, location-level variation became less important and site-level variation became more important with decreasing taxonomic resolution, while for compositional data, the opposite pattern occurred. This suggests that variation in the presence of species or taxa at a particular location along the coast is driven by large-scale processes, while variation in relative abundances within locations is driven by medium-scale processes. 5. The lack of significant variation in the proportional abundances of phyla at large spatial scales suggests that some consistency of pattern may emerge at larger scales (spatial and/or taxonomic), even in the presence of high small-scale variability. These findings strengthen the idea that substantial local variation need not preclude the existence of broad-scale organization in ecological patterns and biodiversity.