Publication Date:
2012-11-21
Description:
Allometric scaling of body size versus growth rate and mortality has been suggested to be a universal macroecological pattern, as described by the Metabolic Theory of Ecology (MTE). However, whether such scaling generally holds in natural assemblages remains debated. Here, we test the hypothesis that the size-specific growth rate and grazing mortality scales with the body size with an exponent of −1/4 after temperature correction, as MTE predicts. To do so, we couple the dilution experiment with the FlowCAM imaging system to obtain size-specific growth rates and grazing mortality of natural microphytoplankton assemblages in the East China Sea. This novel approach allows us to achieve highly resolved size-specific measurements that could be hardly obtained in traditional size-fractionated measurements using filters. Our results do not support the MTE prediction. The size-specific growth rates scale positively with body size (with scaling exponent ~ 0.1), and the size-specific grazing mortality is independent of body size. Furthermore, results of path analysis indicate that size-specific grazing mortality is mainly determined by size-specific growth rate. We further investigate how the variation of size-specific growth rate and grazing mortality can interact to determine the microphytoplankton size structure, described by Normalized Biomass Size Spectrum (NB-SS). We test if the variation of microphytoplankton NB-SS slopes is determined by (1) differential grazing mortality of small versus large individuals, (2) differential growth rate of small versus large individuals, or (3) combinations of these scenarios. Our results indicate that the relative grazing mortality of small over large size category best explains the variation of NB-SS slopes across environments. These results suggest that higher grazing mortality of small microphytoplankton may release the large phytoplankton from grazing, which in turn leads to a flatter NB-SS slope. This study contributes to an understanding of the relative importance of bottom-up versus top-down control in shaping the microphytoplankton size structure.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
Permalink