Ecological Studies On Food Web Structures And Trophic Relationships Of Cave Ecosystem Using Stable Isotopes

The structure and trophic relationship of food webs are fundamental research topics in modern ecology. Food webs are important for the understanding of patterns and processes of an ecosystem. Stable isotopes of carbon and nitrogen, as a powerful approach to study the structure and dynamics of food webs and trophic relationships, have been increasingly used in the studies on a wide variety of ecosystems. In the thesis, I gave on overall review on sample preparation, analysis, interpretation and application of stable isotope ratios (δ13C andδ15N) in ecological studies in several caves of the country of Yangshuo, Guangxi province, with the main results and conclusions as follows.The study, the compare of theδ13C andδ15N values of the soil organic matters in the different light belts and theirs values of the diplopod groups in the opposite light belts of the Tianyan cave, found that theδ13C andδ15N values of the soil organic matters in the different light belts are different. Theδ13C andδ15N values are bigger and bigger from the light belt to the dark belt. The microbe decomposing the organic matters in soil and the fractionation of the stable isotopes indicated the changes of the values. The correlation analysis on theδ13C value of the soil organic matters in the different light belts and the its value of the diplopod groups in the opposite light belts found that theirδ13C values are closely positive related. The similarδ13C values in the soil organic matters in the different light belts and the diplopod groups in the opposite light belts indicate that the soil organic matters was the major food source for the diplopod groups.We investigated differences inδ13C andδ15N of soil organic matters between different caves, Jiandaoyu cave and Tianyan cave which located in Yangshuo country, Guangxi province. The Jiandaoyu cave, which was polluted severally by organic waste and animal dejection,δ13C andδ15N was significantly higher in the light belt of the Jiandaoyu cave than that of in the light belt of the Tianyan cave. Similarly,δ13C andδ15N was higher in the reflection light belt of the Jiandaoyu cave than that of the opposite the light belt of the Tianyan cave. However,δ13C andδ15N values of the soil organic matters in the dark belt of the Jiandaoyu cave was almost the same asδ13C value of the soil organic matters in the dark belt of the Tianyan cave. High external nutrient loading are responsible for the high sedimentδ13C andδ15N of the soil organic matters, respectively. The difference of the stable isotope signatures between the two caves observed in this study demonstrated the dynamic nature in isotopic signatures of different polluted degree of caves.Stable carbon and nitrogen isotopes were used to investigate food web and to determine the importance of carbon sources in Dongfeng cave. The result indicated the food chains were mainly gnawer food chains. Stable carbon isotopic signatures suggested that the soil organic carbon sources were the main carbon sources in the food web of the Dongfeng cave. The△δ15N, which was calculated by the mainly prey relation, was 1.16‰. Soil organic matters was the primary production. The primary consumers were diplopod groups, Opeas gracile (soil animal), Noctuidae, Distrammena mamorara ,The spiders groups, Systenocentrus sp. , Geophiidae and Bufo mdanostictus were secondary consumers.