| Summary: | 碩士 === 國立臺灣大學 === 生物環境系統工程學研究所 === 99 === Scales could be regarded as windows for viewing through an ecosystem. Patterns enable scientists to view through systems with logical perspectives and thus are considered as key elements for illustrating natural conjunctions in an ecosystem. Yet, physical and biological patterns operating over a rage of spatial and temporal scales are able to determine the ecological patterns. To emphasize the importance of scaling in ecological fields, this study elucidates how fish and environment are associated through spatial and temporal scales under a hierarchical structure and also examined how the relationships differ among species. Sicyopterus japonicus and Varicorhinus barbatulus are fishes chosen as survey species on account of their characteristics and distributions. Both species are migratory fishes with identical movement patterns among seasons in a year. Density of the fishes and environment variables were investigated and quantified at 70 stream sections distributed among 14 reaches in the Datun stream catchment of northern Taiwan during the autumn and winter of 2007, as well as the spring and summer of 2008. Hierarchical linear generalized models (HGLMs) and hierarchical linear models (HLMs) were applied to describe the relationships between 16 environment variables and the fish density of each species. The HGLM result suggests that V. barbatulus are dependent to larger-scale, migratory-related variables – elevation, salinity and water temperature. HLM result shows that S. japonicus relates to the habitat variables at both section (current velocity and water depth) and reach (stream width, water temperature, slope, river mile and soil erosion index) levels. Cross-level interactions (depth and river width, depth and soil) could be found in winter HLM. In general, the results indicate that each species responds to the environment majorly under a specific or a range of scale according to their characteristics and life cycles. S. japonicus respond to a spatially smaller-scale habitat environment; in contrast, V. barbatulus respond to relatively greater spatial scale environment features. Eventually, a diagram explicitly illustrating the cross-level relationships between fish and environment was then provided for conceptualizing the biotic-abiotic interaction in Datun stream. In conclusion, this research has provided a measurement for discovery the potential environment variables that might have caused influence on fish distribution in streams under different spatial and temporal scales; meanwhile, yielded the essentiality of considering seasonal changes while observing patterns of certain species.
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