SPATIAL AND TEMPORAL VARIATION IN LITTORAL-ZONE FISH COMMUNITIES - A NEW STATISTICAL APPROACH

Through the use of principal coordinates analysis, a technique is pres ented that allows the quantitative partitioning of the total variation within a data set into its spatial and temporal components. The graph ical nature of this technique, in combination with the quantitative re sults, aids in the examination of specific hypotheses regarding the st ructure of the variation. These hypotheses are tested against null or model matrices of the structure of the variation with statistical sign ificance assessed using Mantel's test. This approach is applied to a d ata set of species' abundances from the littoral-zone fish communities of three Ontario lakes sampled three separate times. The variation wa s partitioned and the influence of different similarity measures was e xplored. Among-lake (spatial) variation accounted for 67-81% of the to tal variation. The time of sampling represented 1-3% of the total. The re was significant among-lake variation for all three sampling periods whereas only one lake showed a significant temporal component. Togeth er, both lake and time of sampling accounted for 74-86% of the variati on, the remainder being within-lake variation (i.e., among-site or sit e-by-time interactions). The structure of the variation was sensitive to the similarity measure used as a result of differing emphasis on pa rticular attributes (e.g., relative versus absolute abundance).