Asymmetry in the thermal sensitivity of predator and prey performance may explain T-S and Bergmann’s rules in zooplankton

Numerous studies have demonstrated an inverse correlation between ambient temperature and body size in various ectotherms. This pattern could be explained by the greater temperature effect on the predator’s foraging rate and, in turn, on the mortality rate in comparison to the birth rate in prey populations. While a number of studies have revealed that the latter effect is close to the one anticipated by the Q 10  = 2 assumption, the hypothesis would be confirmed if the effect of temperature on the foraging rate of the predator was greater than Q 10  = 2. To test this hypothesis, we compared the capture rate and SMR of two fish species (rudd and Malabar danio) and several parameters characterising the mobility of the fish and their planktonic prey ( Daphnia ) at different temperatures. Although the Q 10 for SMR was only around 2, the capture rate increased with rising temperatures much more than expected from the Q 10  = 2 assumption, which confirmed our hypothesis. The most likely explanation seems to be a much greater increase of mobility and, in turn, reaction field volume of the fish than of its planktonic prey at elevated temperatures, which improves its attack rate more than predicted by the Q 10  = 2 assumption.