应用稳定同位素研究广西东方洞食物网结构和营养级关系

稳定性同位素技术已经成为研究生态系统食物网结构和营养级关系及其动态变化的重要手段。应用稳定同位素技术(δ13C和δ15N)研究了东风洞的食物网结构和营养级关系。研究结果表明,东风洞主要为腐食食物链,由于在洞穴内黑暗带中无光照也无植物生长,所以碳源主要为东风洞中的土壤有机质,作为第一营养级;主要摄食关系为马陆与土壤有机物质,螺类与土壤有机物质等;在该洞生态系统中,将3种马陆直接作为初级消费者,以隅蛛和其它马陆平均值之间的差值(2.04‰)作为东风洞食物网稳定氮同位素的富集因子。根据营养级模型可知,马陆类群、细长钻螺等土壤动物,裸灶螽和涂闪夜蛾形成第二营养级,即初级消费者;第三营养级包括蜘蛛类、盲蛛、地蜈蚣以及黑眶蟾蜍,为次级消费者。

The studies on the food web structures and trophic relationships in Guangxi Dongfang Cave by means of stable carbon and nitrogen isotopes

The stable carbon and nitrogen isotope technology is an effective method to study the structure and dynamics of food webs and trophic relationships in ecosystems.The stable carbon and nitrogen isotopes(δ13C and δ15N) are used to investigate food web and trophic relationships of the Guangxi Dongfeng Cave in this study.The Dongfeng cave located in Fuwang Village,Putao Town,Yangshuo County,Guangxi Province was investigated in July 2007.In this cave,13 animal samples and 3 soil samples were collected for estimation of δ13C and δ15N.The results indicated the great range of δ13C values from-19.83‰(Pholcus crypticolens) to-27.27‰(Sypna picta).The samples of Pholcus crypticolens and Steatoda phalerala have higher δ13C values than other spider groups,since the food source of the two species contains other insects.The range of δ15N value is from 2.62‰(soil organic matter) to 5.64‰(Geophiidae).The enrichment of δ15N in the food-web is more obvious than that of δ13C.For example,the different value of δ15N between diplopod and soil organic value is 1.16‰,and the difference of δ15N value Distrammena sp.and Sypna picta from soil organic matters is from 1.24‰ to 1.36‰.The gnawer food chains take a main role in the Dongfeng cave,because there is no illumination and plant in the dark area of the cave,and the soil organic matters is the main carbon sources as the first trophic level.The mainly prey relations are diplopod or snails to soil organic matters etc.In the ecosystem of this cave,3 species of diplopod are the primary consumers,and the difference value(2.04‰) between Tegettaria sp.and other diplopods is the enrichment ratio of the stable nitrogen isostope of the food-web in Dongfeng cave.According to trophic model,the primary consumers are soil animals(such as diplopod groups,and Opeas gracile),Sypna picta,and Distrammena sp.,as the second trophic level(that is the primary consumers).The third trophic level includes spiders groups,Systenocentrus sp.,Geophiidae,and Bufo mdanostictus as the secondary consumers.The composition of δ13C and δ15N or the enrichment ratios to δ15N at all levels of consumers in the karst caves are generally lower than those in the earth surface ecosystem where on the composition and the enrichment ratio of δ15N,Passer montanus in Maduo County of Qinghai Province has(7.77±0.53)‰,Macrobrachium nipponense and Carassius auratus in Xingzi County of Jiangxi Province(14.3±0.5)‰ and(10.8±0.9)‰ respectively.Their average enrichment ratio of δ15N among different trophic levels of the earth surface ecosystem is(3.4±1.1)‰.In the Dongfeng cave,however,the highest value of δ15N is Geophiidae(5.64‰),and the enrichment ratio of ecosystem is only 2.04‰.Its reasons of low enrichment may be the effect of food source and life metabolism on δ15N of living beings in karst caves where there are poor food,small life body,low oxygen consumption,and low metabolic process.