Quantifying temporal variation in heterobranch (Mollusca: Gastropoda) sea slug assemblages: tests of alternate models

Assemblages of heterobranch sea slugs are notoriously variable in space and time which has sometimes led to their exclusion from broader studies of patterns of biodiversity. This variability may also result in a failure to detect underlying spatial and temporal patterns. Assemblage data (species abundances) from three intertidal sites over a period of 13 months, were used to compare the conclusions drawn from three different analytical approaches—a non-specific test for differences among months, and tests of cyclicity, and seriation, using specific model matrices. While no significant difference was detected for the non-specific test (i.e. concluding no significant temporal variation), the data were significantly correlated to both model matrices with the cyclicity model outperforming the seriation model at two of the three sites. The study also highlighted the spatial variability of assemblages over a scale of just a few kilometres. Wider testing using previously published datasets confirmed the utility of these models for exploring specific hypotheses about patterns of temporal change.