| Summary: | 碩士 === 國立成功大學 === 生物學系碩博士班 === 92 === The cohort life table and the population dynamics of the gastropoda snail Thiara riqueti (Grateloup, 1840) in Su-Tsao estuary in Tainan and Taiwan were studied during July 2000 and 2004. The cohort life histories of the Thiara riqueti at four temperature and seven salinity combinations were analyzed based on the age-stage, two-sex life table to take into consideration the variable development rates among individuals. At 30℃ and salinity 2.0%, the intrinsic rate of increase (r) is 0.1412 week-1, while the finite rate of population increase (λ) is 1.1516 week-1. The net reproductive rate (Ro) is 56.33 offspring and the mean generation time (T) is 28.65 weeks. These population parameters shows that temperature 30℃ and salinity 2.0% is the best condition among all treatments. Among different wild habitats, the habitat B offers the best condition for T. riqueti and the intrinsic rate of increase, the finite rate of population increase, the net reproductive rate and the mean generation time are 0.1441 week-1、1.155 week-1、5.50 offspring and 11.84 weeks, respectively. The population parameters suggested that T. riqueti is r-strategist. This species shown a single peak of recruitment per annum during the period of summer to fall. In Su-Tsao estuary, only female T. riqueti were observed, as is typical of most population of this species. Snails with shell length over 4.0mm had full-developed larvae in the brood pouch during the study period. Temperature and salinity are the major environmental factors for fecundity. The lowest densities were found in the habitats E, F and G and the highest ones in habitats A, B, C and I during the study period. The population densities in habitats A, B and C were influenced by the sulfate, dissolved oxygen, pH, salinity and nitrate during 2000-2001. Evidence was found that the life table and population dynamics of T. riqueti were dependent on the seasonal variation of environmental factors of the estuary hydraulic regime.
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