2018-09-252024-05-13https://scholars.lib.ntu.edu.tw/handle/123456789/646244Abstract: Body size is the key trait that regulates predator-prey interactions. The body size ratio of predator and prey, i.e. predator-prey mass ratio (PPMR), has been shown related to trophic transfer efficiency and food web dynamics. Community PPMR is also an important parameter to construct size-based plankton food web model. However, what environmental factors determine zooplankton community PPMR remains elusive in natural systems. We use size-fractionated stable isotope analysis (SIA) of natural plankton community to estimate community PPMR. First, we test the hypothesis I: high resource quantity and/or preferred stoichiometry decreases community PPMR, given that high resource quantity and quality increases the proportion of large-size prey species. Furthermore, change of prey size distribution may not explain all the variation of community PPMR. Thus secondly, we test the hypothesis II: prey size selectivity exhibited by predatory zooplankton community is affected by zooplankton feeding strategy and taxonomic composition. To assess the prey size selectivity, we calculate the difference between realized PPMR (calculated from SIA) and environmental PPMR (calculated from prey size composition in the environment, assuming that feeding of predators depends only on prey relative density in the environment) as the proxy. Specifically, community size selectivity skews to large size when active ambush predators (preferring large prey) dominate the zooplankton community. We expect that this field observation will depict a more comprehensive picture of the ecological mechanisms determining community PPMR, which is critical to our understanding of food web dynamics.