Mean Shift是目前为止特征空间分析的最好方法之一,但其分割结果受带宽参数的影响。图像粗糙度是与视觉感受相关的图像纹理特征,对图像纹理的描述能力很强。图像像素的平均偏移量也体现了图像像素的总体离散情况。通过对高斯核函数的创...Mean Shift是目前为止特征空间分析的最好方法之一,但其分割结果受带宽参数的影响。图像粗糙度是与视觉感受相关的图像纹理特征,对图像纹理的描述能力很强。图像像素的平均偏移量也体现了图像像素的总体离散情况。通过对高斯核函数的创建以及图像粗糙度的描述,创新性地给出了Mean Shift的窗口尺寸选择方法以及图像像素平均偏移的计算,仿真结果表明,该算法对不同类型的图像,均能得到令人满意的效果。展开更多
Low-head dam impoundments modify local habitat and alter fish assemblages; however, to our knowledge, the pattern of how fish assemblages in the impoundments relate to local habitat, tributary position, and dam charac...Low-head dam impoundments modify local habitat and alter fish assemblages; however, to our knowledge, the pattern of how fish assemblages in the impoundments relate to local habitat, tributary position, and dam characteristics is still unclear. We used data collected in 62 impoundments created by low-head dams Jn headwater streams of the Qingyi River, China, to examine relationships between fish assemblages and local habitat, tributary position, and dam characteristics. We also assessed the relative importance of the three groups of factors in determining fish species richness and composition. Linear regression models showed that fish species richness was related to substrate heterogeneity, confluence link, and dam number upstream. Redundancy analysis showed that fish species compositions were influenced by substrate heterogeneity, confluence link, dam height, dam numbers upstream and downstream. Overall, dam characteristics were more important in affecting fish species richness but less important in determining fish species composition than local habitat （i.e., substrate heterogeneity） and tributary position. Our results suggest that low-head dam may affect fish species richness in impoundments by modifying local habitat and constraining fish movement, and the relative abundances of those fish species may depend more on species habitat presences and stream size than on impoundment size and number.展开更多
基金Foundation items： This work was supported by grants from the Natural Science Foundation of China （NSFC 31172120, 31372227, 31500452）
文摘Low-head dam impoundments modify local habitat and alter fish assemblages; however, to our knowledge, the pattern of how fish assemblages in the impoundments relate to local habitat, tributary position, and dam characteristics is still unclear. We used data collected in 62 impoundments created by low-head dams Jn headwater streams of the Qingyi River, China, to examine relationships between fish assemblages and local habitat, tributary position, and dam characteristics. We also assessed the relative importance of the three groups of factors in determining fish species richness and composition. Linear regression models showed that fish species richness was related to substrate heterogeneity, confluence link, and dam number upstream. Redundancy analysis showed that fish species compositions were influenced by substrate heterogeneity, confluence link, dam height, dam numbers upstream and downstream. Overall, dam characteristics were more important in affecting fish species richness but less important in determining fish species composition than local habitat （i.e., substrate heterogeneity） and tributary position. Our results suggest that low-head dam may affect fish species richness in impoundments by modifying local habitat and constraining fish movement, and the relative abundances of those fish species may depend more on species habitat presences and stream size than on impoundment size and number.
