Data from: Systematic deviations from linear size spectra of lake fish communities are correlated with predator-prey interactions and lake-use intensity

Size structure of organisms at logarithmic scale (i.e. size spectrum) can
often be described by a linear function with a negative slope; however,
substantial deviations from linearity have often been found in natural
systems. Theoretical studies suggest that greater nonlinearity in
community size spectrum is associated with high predator-prey size ratios
but low predator-prey abundance ratios; however, empirical evaluation of
the effects of predator-prey interactions on nonlinear structures remains
scarce. Here, we aim to empirically explore the pattern of the
size-specific residuals (i.e. deviations from the linear regression
between the logarithmic fish abundance and the logarithmic mean fish size)
by using size spectra of fish communities in 74 German lakes. We found
that nonlinearity was strong in lakes with high predator-prey abundance
ratios but at low predator-prey size ratios. More specifically, our
results suggest that only large predators, even if occurring in low
abundances, can control the density of prey fishes in a broad range of
size classes in a community and thus promote linearity in the size
spectrum. In turn, the lack of large predator fishes may cause high
abundances of fish in intermediate size classes, resulting in nonlinear
size spectra in these lakes. Moreover, these lakes were characterized by a
more intense human use including high fishing pressure and high total
phosphorus concentrations, which have negative impacts on the abundance of
large, predatory fish. Our findings indicate that nonlinear size spectra
may reflect dynamical processes potentially caused by predator-prey
interactions. This opens a new perspective in the research on size
spectrum, and can be relevant to further quantify the efficiency of energy
transfer in aquatic food webs.