Zoological Studies

A Structural Equation Model for Physiochemical Variables of Water, Benthic Invertebrates, and Feeding Activity of Waterbirds in the Sitsao Wetlands of Southern Taiwan

Shih-Hsiung Liang, Bao-Sen Shieh and Yaw-Syan Fu (2002) We used structural equation modeling to explore the relationships between benthic invertebrates and physiochemical variables of water, and investigated their direct and indirect effects on waterbird feeding activities. Sixteen sites located in the Sitsao wetlands of southern Taiwan were sampled on a monthly basis from Sept. 1997 to Aug. 1998. Factor analysis identified 1 factor for physiochemical variables and 2 factors for benthic invertebrates. We classified waterbirds into 10 feeding groups, and factor analysis of the feeding activities of these groups suggested 3 feeding factors. Therefore, we used 6 factors to construct an initial model examining their causal relationships to each other and then modified the models to obtain more significant paths. Results indicate that water depth affected all 3 waterbird feeding factors, and salinity influenced only the small-invertebrate factor, which in turn directly affected the surface-feeding factor. Daily lowest water temperature affected only the wading-feeding factor in the final model. To further examine the final structural model, we used repeated measures ANOVA to analyze temporal variations in variables among the 4 types of wetlands: unused salt fields, abandoned fish ponds, active fish ponds, and mangroves. Three related variables (salinity, the small-invertebrate factor, and the surface-feeding factor) varied significantly among wetland types, although the differences did not significantly change from month to month. We conclude that the results of structural equation modeling combined with repeated measures ANOVA provide important information that can be useful in managing the Sitsao wetlands for different feeding groups of waterbirds.