| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 93 === Abstract
Drought in inland waters is one of the most important disturbances that affect community compositions of macroinvertebrates in these water ecosystems. Although there had been many researches on the effect of drought on lotic ecosystems, most of them were studied in temperate or arid region with an obviously wet and dry season in a year. But there has been no study that has quantified the drought disturbance and been carried out in subtropical areas. In this study, the drought disturbance was quantified by the ratio of the number of days that streambeds were dry to the total number of days in the sampling period. Eight sampling sites with different drought ratios were selected along Hapen Creek located in northeastern Taiwan. Macroinvertebrates were collected at each site every two weeks from September 2003 to July 2004 by a Surber’s sampler (area = 50 x 50 cm2; mesh size = 250μm). There were significant differences in taxa richness, number of individuals, Shannon diversity index, and Pielou evenness index among the 8 sites (ANOVA, p < 0.05). All 4 community parameters decreased with an increase in drought ratio. This result was contradictory to the intermediate disturbance hypothesis. This may be due to a high discharge, which was also an important disturbance in the stream ecosystem. It was found that the macroinvertebrates decreased significantly after a high discharge. In the principal component analysis (PCA), the first component was highly correlated with water depth, current velocity, and discharge, suggesting that drought and high discharge were the important disturbances that influenced macroinvertebate assemblages. Besides the effects of drought and high discharge on macroinvertebrate assemblages, PCA also identified the canopy cover, pH values, and the concentration of phosphate that were important factors affecting the macroinvertebrate assemblages. In this study, it was also found that the macroinvertebrates could recover in a few days after a drought. This was because they could colonize a new patch from refugia very fast, but not resist the drought phase.
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