Grazer and nutrient impacts on epilimnetic ciliate communities
Grazer and nutrient impacts on epilimnetic ciliate communities
复制标题
食草动物和营养对表层纤毛虫群落的影响
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
Asit Mazumder
中科院分区：
文献类型：
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作者：
P. Marchessault;Asit Mazumder
在8个大型围栏中，研究了大型食草动物(水蚤)和营养物质(氮、磷)对纤毛虫群落的影响。在八个围栏中的四个围栏里放养浮游性鱼类(Phoxinus Eos)，形成了水蚤丰度的对比。将硝酸盐和磷酸盐添加到两个有鱼的围栏和两个没有鱼的围栏中，形成了营养方面的对比。无鱼围栏中浮游动物的生物量和平均长度均显著大于有鱼围栏。营养物质和鱼类的添加导致总磷浓度变化四倍，藻类生物量(Chla)变化六倍。在有鱼的围栏里，几乎没有大型水蚤。当大型水蚤丰富时，纤毛虫的丰度要低一到三个数量级。营养物质的添加不会增加带水蚤围栏中纤毛虫的丰度，但这些围栏中的纤毛虫平均长度较大。纤毛虫丰度随着浮游动物生物量的增加而增加，但当大型水蚤丰富时，纤毛虫丰度迅速下降，呈现双曲线格局。当所有处理的数据放在一起考虑时，桡足类生物量和纤毛虫丰度之间没有关系，但当单独考虑有鱼和没有鱼的围栏数据时，出现了正相关关系，尽管不是非常显著。我们的结果表明，大型食草动物是调节纤毛虫群落的最重要因素，也是纤毛虫对营养物质和资源的反应。无论湖泊生态系统的营养状况如何，浮游动物从桡足类向以大型水蚤为主的转变可能会导致纤毛虫丰度的大幅下降。
The effects of large grazers (Daphnia) and nutrients (nitrogen and phosphorus) on epilimnetic ciliate communities were investigated in eight large in situ enclosures. Contrasts in Daphnia abundance were created by stocking planktivorous fish (Phoxinus eos) in four of the eight enclosures. Contrasts in nutrients were created by adding nitrate and phosphate to two enclosures with fish and to two enclosures without fish. Both the biomass and mean length of total zooplankton were significantly greater in the fish‐free enclosures than in the enclosures with fish. Addition of nutrients and fish produced a four‐fold variation in concentration of total epilimnetic phosphorus and six‐fold variation in algal biomass (Chl a). Daphnia were virtually absent in the enclosures with fish. The abundance of ciliates was one to three orders of magnitude lower when Daphnia were abundant. Addition of nutrients did not increase ciliate abundance in enclosures with Daphnia, but ciliate mean lengths were larger in these enclosures. Ciliate abundance increased with increasing zooplankton biomass when Daphnia were lacking, but it declined rapidly when Daphnia were abundant, producing a hyperbolic pattern. When the data for all the treatments were considered together, there was no relationship between copepod biomass and ciliate abundance, but positive relationships, although not highly significant, emerged when the data for enclosures with and without fish were considered separately. Our results suggest that large grazers are the most important factor regulating ciliate communities as well as the responses of ciliates to nutrients and resources. Shifts of zooplankton from copepods to Daphnia dominance may result in large reductions in ciliate abundance, regardless of the trophic status of lake ecosystems.