Abstract: To clarify the niche characteristics of dominant species and community structure of metazooplankton in North Pan River and South Pan River, we collected samples of the metazooplankton in October 2020 (normal period), April 2021 (dry period), and July 2021 (wet period), and evaluated dominance, niche breadth, and niche overlap values. The results showed that a total of 43 species were recorded in North Pan River and South Pan River, including 28 species of rotifers, 3 species of copepods and 12 species of cladophors. Among them, 25 species were common in South Pan River and North Pan River. Keratella cochlearis, Mesocyclops sp., and Nauplius  (larvae) were the dominant species in the three hydrographic periods of South Pan River and North Pan River. The abundance of metazooplankton in South Pan River was 424.58, 1482.08, and 383.10 ind·L^-1 in the wet, normal, and dry periods respectively, and the biomass was 0.397, 0.369, and 0.006 mg·L^-1, respectively. In North Pan River, abundance was 329.33, 553.90, and 117.73 ind·L^-1 in the wet, normal, and dry periods, and biomass was 0.397, 0.369, and 0.006 mg·L^-1, respectively. Dominant species was mainly narrow-niche population (42.86%) in South Pan River, while it was middle-niche population (64.29%) in North Pan River. Niche overlap value and niche breadth changed seasonally due to the changes of environmental factors. The niche breadth of dominant species in South Pan River was significantly different (P<0.01), and the adaptability of dominant species to environment was quite different. There was no difference in niche breadth of dominant species (P>0.05) in North Pan River, and little difference in the ability to adapt to environment among dominant species. The average overlap values of dominant species in the South Pan River and North Pan River were dry period < wet period < normal period (0.328<0.780<0.847 for South Pan River; 0.283<0.508<0.812 for North Pan River). The overlap values between Keratella cochlearis and other dominant species were large. The average overlap value of Keratella cochlearis and other dominant species in South Pan River and North Pan River was 0.68 and 0.56, respectively, being the highest frequency of occurrence of 92.86%, indicating that it had a strong ability to utilize resources. As indicated by community structure and niche characteristics of dominant species of metazooplankton, the competition among dominant species in South Pan River and North Pan River in wet period and normal period was stronger than that in dry period, and the niche of dominant species changed seasonally.

Key words: metazooplankton, community structure, dominant species, niche.