| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 98 === The former genera Helice and Chasmagnathus of mudflat crabs are separated into 6 genera. Except Pseudohelice which is widely distributed over the tropical to subtropical zones, the others distribute in the temperate and the subtropical zones. There are 4 species of this group in Taiwan, Chasmagnathus convexus (De Haan, 1835), Helice formosensis Rathbun, 1931, Helicana doerjesi Sakai, Türkay & Yang, 2006, and Pseudohelice subquadrata (Dana, 1851). The habitats, stomach contents, gastric mills and thermal tolerance of the 4 Taiwanese species are compared to study whether the environmental temperature is the major factor limiting their distribution. H. formosensis can tolerate a wide range of temperature and water quality of environment, but H. doerjesi only restricts in lower tidal zone because it only tolerated the narrowest salinity range. The water content of soil has no difference among the 4 species, but there is significant difference in the grain size. C. convexus and H. formosensis prefer very fine sand, H. doerjesi prefers silt, and P. subquadrata always lives in fine sand habitat. The results of thermal tolerance experiment showed that: (1) there was no difference between sexes of the 4 mudflat crabs and 4 fiddler crabs [Uca arcuata (De Haan, 1835), U. crassipes (White, 1847), U. formosensis Rathbun, 1921, U. lactea (De Haan, 1835)]; (2) The thermal tolerances of 4 fiddler crabs were significantly higher than the 4 mudflat crabs; (3) C. convexus had the lowest thermal tolerance, and P. subquadrata did not appear higher tolerance; (4) Small individuals could tolerate much higher temperature of H. formosensis, H. doerjesi and P. subquadrata; (5) Mudflat crabs had significantly higher thermal tolerance in warm season than that in cool season; (6) Different populations showed different thermal tolerance. The evidence of fiddler crabs had higher thermal tolerance than mudflat crabs support the hypothesis of thermal tolerance can affect the distribution of mudflat crabs. Although P. subquadrata distributes in lower latitude but it did not have higher thermal tolerance which is explained by its sheltered habitat and nocturnal behavior. C. convexus had weak thermal tolerance and it always stays under heavy sheltered vegetation, and forages at night. H. doerjesi inhabits in lower intertidal zone, but did not show lower thermal tolerance. Different vertical zonation might be influenced by the interspecific competition.
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