Seasonal variation of food web structure in subtropical mountain lakes

• Main Authors: Chih-Hsuan Fan, 范芷瑄
• Other Authors: Rita S.W. Yam
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/00720265878969268883

碩士 === 國立臺灣大學 === 生物環境系統工程學研究所 === 104 === Mountain lakes are natural and remoted lentic water bodies with unique ecosystem structure housing high level of biological endemism. They are sensitive to environmental changes though most studies of the mountain lake ecosystems have been focused on the temperate region. Yet, only limited investigation has been undertaken in such ecologically important habitats in tropical/subtropical Asia. As the subtropical mountain lake ecosystems are strongly influenced by seasonal environmental perturbations, such as periodic and stochastic hydrological disturbances due to heavy rainfall events, and the intense solar radiation during summer. It could be the major factor characterizing the energy basis for the lake food webs. In this study, the trophic structure and food utilization patterns of primary consumers, secondary consumers, and top predators in two subtropical mountain lakes in Taiwan, including Lake Tsuifeng (TFL) and Lake Yuanyang (YYL) were investigated using stable carbon and nitrogen isotope analyses. The two study lakes exhibited marked difference in riparian vegetation pattern, TFL was relatively unshaded with only sparsely distributed riparian vegetation whereas YYL was a densely shaded system with continuously distributed riparian forest. This resulted in distinct difference in the availability of different food sources to the food webs. During the study period, the variation of water temperature and precipitation pattern was similar between the two study lakes with most heavy rainfall events in summer. Our results showed that the food web components were more δ13C-enriched in TFL than in YYL. Despite the high availability of the two most dominant allochthonous food sources including fine particulate organic matter (FPOM) and leaf litter in the densely shaded YYL, they were least utilized by aquatic consumers. Instead, results of the stable isotope mixing model (SIAR) indicated that the δ13C-depleted bacteria represented the major energy basis in the allochthonous YYL. In contrast, TFL was a typical autochthonous ecosystem dependent on autochthonous food sources (periphyton and phytoplankton) which accounted for the major primary production supporting the food web. In addition, the increased complexity of food web structures in YYL as compared to TFL could be primarily due to higher habitat complexity in YYL where dense macrophyte bed and accumulation of leaf litter mass on the lake bottom. Moreover, the observed seasonal shift of food web structures in the two study lakes could be due to the enhanced primary production due to higher light intensity and water temperature in summer. Our study confirmed that the most important basal food sources for aquatic organisms in allochthonous YYL was bacteria, whereas autochthonous basal food sources (e.g. phytoplankton and periphyton) had the higher contribution to aquatic organisms in autochthonous TFL during the study periods.