2011-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/697673Abstract: Effects of anthropogenic disturbance and global climate changes on ecosystems are pressing concerns. Developing reliable and efficient indicators to study trophodynamics is essential for ecosystem management and conservation. Aquatic food webs are strongly size-based, and substantial evidence suggests a positive linear relationship between log bodysizes and trophic levels of organisms. Therefore, one potential indicator to investigating trophodynamics is predator-prey mass ratio (PPMR) in foodwebs. Theoretical studies suggest that PPMR is an important parameter to determine the stability, structure, and dynamics of foodwebs. Moreover, PPMR has been used to infer the energy transfer efficiency and foodchain length. However, only one mechanism (gape limitation) was proposed to explain the observed pattern in PPMR so far; nevertheless, this mechanism ignores omnivory and feeding flexibility and gape size is difficult to define for many organisms. Here, we propose to study PPMR in plankton foodweb. We focus on plankton, because they are easy to collect and measure and they play an important role in aquatic foodwebs. Apart from previous hypothesis of gape limitation, we hypothesize that PPMR is determined by the variation of resource availability. This hypothesis is motivated by empirical observations that plankton grazers can select prey based on quantity and quality of food. To test the hypothesis, we use two factors as proxy for resource availability: (1) quantity: plankton biomass in different size classes (size distribution) and (2) quality: C:N:P ratio of plankton. In practice, we will use nitrogen stable isotope analysis to assess PPMR within plankton communities. The quantity of plankton biomass in different size classes will be estimated by FlowCam and ZooScan, automatic imaging systems that can be used to measure plankton size and biomass efficiently. The quality of plankton will be measured using elemental analyzer and chemical methods. Furthermore, environmental variables such as nutrient, light, temperature, and salinity will be collected accompanying plankton samples in order to evaluate environmental conditions that determine resource availability. We test the hypothesis in both freshwater (Feitsui Reservoir) and marine (East China Sea) systems.stable isotopepredator-prey mass ratioresource availabilityC:N:P ratiosize distributionfood chain length