Discussion
We believe that our study provides a robust test of Bergmann’s Rule because it is the largest study to date (based on 100,326 samples and 388 taxa within an order), is near-global in its distribution, and it applies a statistical approach that allows us to disentangle multiple correlated predictors. We show that marine copepods follow Bergmann’s Rule, with a strong decline in copepod body size with temperature, as reported by Evans et al. (2020). We also found that temperature was more important than latitude or concentration of dissolved oxygen, and that food availability was of similar importance to temperature, contrary to the findings by Brun et al. (2016), who found that body size was much more strongly related to food availability than to temperature. Nevertheless, our results corroborate findings by Brun et al. (2016) that copepod size decreases where more food is available. This contrasts with most previous work on copepods (Vidal 1980), nematodes (Andriuzzi & Wall 2018), lizards (Pafilis et al. 2009) and mammals (Huston & Wolverton 2011), which found that body size increases with food availability. We also found an increase in body size with increased abundance of predators, albeit that the effect size is small.