| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
The winter population dynamics of the cladoceran Daphnia were investigated in Lakes Kizaki, Misuzu and Tamizo, of which two lakes (Misuzu and Tamizo) were covered with ice. It was found that Daphnia survived as free-living individuals during winter in Lakes Kizaki and Misuzu, suggesting that the low water, temperature (<4℃) does not give serious damage to the Daphnia populations. However, the Daphnia individuals had no eggs and therefore the populations had low productivities in winter. Laboratory experiments have shown that low water temperature and low food abundance do not kill Daphnia but suppress their reproduction, but that the Daphnia start reproduction rapidly if temperature and food density increases. This may be a strategy of the Daphnia populat ions to survive winter and competition with other zooplankton species in spring. Climatic warming must increase water temperature in winter. It is considered that the increased lake water temperature in winter due to climatic warming may disturb the Daphnia's strategy.
Filed observation in Lake Suwa has demonstrated that the copepods Acanthcyclops and Eodiaptomus show clear seasonal succession : Dominance of the former in spring to that of the latter in summer. In order to assess the impact of temperature on their seasonal succession, zooplankton communities were maintained in mesocosms in the laboratories, where temperatures were controlled, and changes in the zooplankton community structure were analyzed. Acanthcyclops appeared abundantly in the mesocosms with the spring water temperatures while did not with the summer water temperatures. On the other hand, Eodiaptomus became dominant both under the spring and summer water temperatures. The results have suggested that seasonal dynamics of the Acanthcyclops population in Lake Suwa are controlled directly by wafer temperature, while that those of the Eodiaptomus population are done indirectly through biological interactions mediated by temperature.
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