The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and ...The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and the spring of 2001. Hierarchical agglomerative cluster method and bootstrap randomization were used to identify significant trophic groups for each fish assemblage in the southern Huanghai Sea. A total of six major trophic groups were identified within this system, which classified predators based upon location in the water column or prey size （ i. e. , benthic to pelagic predators or fish to small invertebrate prey predators）. The similarity level used to identify significant trophic groups in each assemblage ranged from 24% to 34%. Although planktivores were the dominant trophic group in each assemblage （60% - 79% ）, there were spatial and temporal variations in the trophic structure, which reflected the differences in the abundance and availability of dominant preys. Simplified food webs were constructed to evaluate the most important trophic relationships between the dominant prey taxa and the fishes in each assemblage within this system. Although there were some differences in the key prey species among different food webs, pelagic prey items （mainly euphausiids and copepods） represent the most important energetic link between primary producers and higher trophic level predators. The trophic level for most fishes was between 3 and d, and the weighted mean trophic level for each assemblage ranged from 3.3 to 3.4. Compared with previous study in the mid-1980s, there was an obvious downward trend in the trophic level for most fish species, which resulted mainly from the fluctuation in key prey species in the Huanghai Sea. The decrease in the importance of Japanese anchovy seems to be offset by other abundant prey species such as Euphausia pacifica and copepods （ mainly Calanus sinicus ） .展开更多
Chromosome segmentation is the most important step in the automatic chromosome analysis system. Since in almost every metaphase image partial touching and overlapping of chromosomes are a common phenomenon, how to sep...Chromosome segmentation is the most important step in the automatic chromosome analysis system. Since in almost every metaphase image partial touching and overlapping of chromosomes are a common phenomenon, how to separate these chromosomes correctly is a difficult yet vital problem. A number of attempts have been made to deal with this problem. This paper is focused on these attempts. Some algorithms are investigated. The principle and the realization of these algorithms are analyzed. Results of these algorithms are compared and discussed.展开更多
根据2005年4～5月在黄海海域进行的春季定点底拖网调查，采用稳定同位素技术和聚类分析方法，研究南黄海低营养层次鱼类中的代表性种类，鳀鱼（Engraulis ja ponicus）和赤鼻稜鳀（Thrissa kammalensis）摄食的食物组成、相似指数及二...根据2005年4～5月在黄海海域进行的春季定点底拖网调查，采用稳定同位素技术和聚类分析方法，研究南黄海低营养层次鱼类中的代表性种类，鳀鱼（Engraulis ja ponicus）和赤鼻稜鳀（Thrissa kammalensis）摄食的食物组成、相似指数及二者对食物竞争的激烈程度．结果显示：1）〉900μm浮游动物、500～900μm浮游动物和仔稚鱼3种饵料为南黄海鳀鱼和赤鼻稜鳗的主要摄食对象；2）二者所摄食的食物组成高度相似，相似指数为65．97％；3）在81～100mm叉长组内的食物平均重叠系数为97．95％，101～105mm内为77．96％，116～120mm内为7．28％，表明南黄海鳀鱼与赤鼻稜鳀在一定环境下对食物可能存在激烈的竞争．展开更多
基金The National Natural Science Foundation of China under contract No.30490233the National Basic Research Program ("973"Program) of China under contract Nos2006CB400608 and 2005CB422306
文摘The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and the spring of 2001. Hierarchical agglomerative cluster method and bootstrap randomization were used to identify significant trophic groups for each fish assemblage in the southern Huanghai Sea. A total of six major trophic groups were identified within this system, which classified predators based upon location in the water column or prey size （ i. e. , benthic to pelagic predators or fish to small invertebrate prey predators）. The similarity level used to identify significant trophic groups in each assemblage ranged from 24% to 34%. Although planktivores were the dominant trophic group in each assemblage （60% - 79% ）, there were spatial and temporal variations in the trophic structure, which reflected the differences in the abundance and availability of dominant preys. Simplified food webs were constructed to evaluate the most important trophic relationships between the dominant prey taxa and the fishes in each assemblage within this system. Although there were some differences in the key prey species among different food webs, pelagic prey items （mainly euphausiids and copepods） represent the most important energetic link between primary producers and higher trophic level predators. The trophic level for most fishes was between 3 and d, and the weighted mean trophic level for each assemblage ranged from 3.3 to 3.4. Compared with previous study in the mid-1980s, there was an obvious downward trend in the trophic level for most fish species, which resulted mainly from the fluctuation in key prey species in the Huanghai Sea. The decrease in the importance of Japanese anchovy seems to be offset by other abundant prey species such as Euphausia pacifica and copepods （ mainly Calanus sinicus ） .
文摘Chromosome segmentation is the most important step in the automatic chromosome analysis system. Since in almost every metaphase image partial touching and overlapping of chromosomes are a common phenomenon, how to separate these chromosomes correctly is a difficult yet vital problem. A number of attempts have been made to deal with this problem. This paper is focused on these attempts. Some algorithms are investigated. The principle and the realization of these algorithms are analyzed. Results of these algorithms are compared and discussed.
文摘根据2005年4～5月在黄海海域进行的春季定点底拖网调查，采用稳定同位素技术和聚类分析方法，研究南黄海低营养层次鱼类中的代表性种类，鳀鱼（Engraulis ja ponicus）和赤鼻稜鳀（Thrissa kammalensis）摄食的食物组成、相似指数及二者对食物竞争的激烈程度．结果显示：1）〉900μm浮游动物、500～900μm浮游动物和仔稚鱼3种饵料为南黄海鳀鱼和赤鼻稜鳗的主要摄食对象；2）二者所摄食的食物组成高度相似，相似指数为65．97％；3）在81～100mm叉长组内的食物平均重叠系数为97．95％，101～105mm内为77．96％，116～120mm内为7．28％，表明南黄海鳀鱼与赤鼻稜鳀在一定环境下对食物可能存在激烈的竞争．
