Zoological Studies

Vol. 39 No. 3, 2000

Community Structure and Functional Organization of Aquatic Insects in an Agricultural Mountain Stream of Taiwan: 1985-1986 and 1995-1996

Sen-Her Shieh* and Ping-Shih Yang**

Department of Entomology, National Taiwan University, Taipei, Taiwan 106

Sen-Her Shieh and Ping-Shih Yang (2000) Changes in stream water and habitat quality of Chichiawan Stream, which flows through Wulin Farm in central Taiwan, were examined using community structure and functional organization of aquatic insects at 4 sites in 1985-1986 and 1995-1996. Long-term records of water chemistry for the study area indicate that water quality in 1995-1996 had not degraded as compared with data in 1987-1988. It was found that there were significant differences in the number of taxa and number of individuals per sample unit for samples at all sites combined between 1985-1986 and 1995-1996. In general, the number of taxa and number of individuals per sample unit were higher in 1985-1986 than in 1995-1996 at the 4 sites. Higher relative abundances of Baetis spp., Rhithrogena ampla, Cincticostella fusca, and Uenoa taiwanensis were found in 1985-1986 compared to 1995-1996, suggesting that the substrate quality of the stream had deteriorated at sites located in agricultural areas. Similar results were found between the taxonomic and functional feeding group analyses when the percentage similarity analysis was used. The functional organization and community composition of aquatic insects at sites 1 and 2 in 1995-1996 were similar to those at site 4 in 1985-1986. Site 4 is located downstream of the confluence between Chichiawan Stream and Yousheng Stream where the stream watershed has been developed for agricultural land use. Principal component analysis (PCA) indicated that, in addition to the substrate quality of the stream, water temperature, dissolved oxygen, conductivity, and ammonia were the most important physicochemical variables shaping the aquatic insect community structure in the study stream reach. The study sites in agricultural areas had poorer stream water and habitat quality. The raw cropping of orchards and vegetable farms greatly increased soil erosion and suspended solids inputs to the stream which may have been harmful to the aquatic insect communities.

Key words: Biological monitoring, Agricultural activities, Functional feeding groups, Chichiawan Stream.

*Correspondence: Current address: National Museum of Natural Science, No. 1 Kuan-Chien Rd., Taichung, Taiwan 404. Tel: 886-2-23627023. Fax: 886-2-23632699. E-mail: senher@mail. nmns.edu.tw, psyang@ccms.ntu.edu.tw