Linking secondary structure of individual size distribution with nonlinear size–trophic level relationship in food webs

Abstract

Existing individual size distribution (ISD) theories assume that the trophic level (TL) of an organism varies as a linear function of its log‐transformed body size. This assumption predicts a power‐law distribution of the ISD, i.e., a linear relationship between size and abundance in log space. However, the secondary structure of ISD (nonlinear dome shape structures deviating from a power‐law distribution) is often observed. We propose a model that extends the metabolic theory to link the secondary structure of ISD to the nonlinear size–TL relationship. This model is tested with empirical data collected from a subtropical reservoir. The empirical ISD and size–TL relationships were constructed by FlowCAM imaging analysis and stable isotope analyses, respectively. Our results demonstrate that the secondary structure of ISD can be predicted from the nonlinear function of size–TL relationship and vice versa. Moreover, these secondary structures arise due to (1) zooplankton omnivory and (2) the trophic interactions within microbial food webs.

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