Ordination of zooplankton community data to detect pesticide effects in pond enclosures

Trends in community structure of crustacean zooplankton among 17 forest pon d enclosures (5 m X 5 m X 1 m deep) were examined and analyzed to determine effects of two candidate forest pesticides, Eight enclosures were treated at two concentrations of an experimental insecticide, tebufenotide; five we re treated at two concentrations of a biological herbicide, bialaphos; and four served as controls. Zooplankton community structure was characterized by ordination of species assemblages using principle components analysis (P CA) and correspondence analysis (CA). Two-dimensional plots of the first tw o axes from PCA and CA were constructed to explore temporal and treatment-r elated patterns in community structure. The first four axes of both ordinat ion functions were used as multivariate descriptors of community structure and were examined for differences among treatments by ANOVA. Species ordina tion plots and sorted rotated factor loadings provided objective means of i dentifying the species important in determining divergence in community str ucture. These were considered indicator species and were examined for diffe rences among treatments by ANOVA and specified contrasts. The ordination an d subsequent analysis revealed trends in community structure and sample dif ferences that indicated clear, concentration-dependent effects of bialaphos and equivocal effects of tebufenotide.