Bergmann's rule reviewed for Endotherms & Ectotherms

A lot of research has been done regarding Bergmann‟s rule. Bergmann‟s rule means that from the surface area to volume ratio it becomes clear that warm-blooded animals, from the same species, tend to be larger at higher latitudes and in cooler climates. But in the literature Bergmann‟s rule is revised in the time and also the mechanism behind the pattern of latitudinal body size variation is debated among researchers. Therefore this thesis deals with two goals. The first goal is to give a first impression whether both endotherms and ectotherms are following the trend of larger size at higher latitudes in the same strength. Therefore I compiled correlation coefficients of endothermic and ectothermic species of the literature. I found that endotherms are strongly following the pattern of large size at higher latitudes (~90%), whereas ectotherms follow it (50%), but not as strong as the endotherms. The second goal is to discuss whether the heat conservation mechanism, as originally proposed by Bergmann is a more or less valid explanation for latitudinal body size variation than other proposed mechanisms in the literature. I suggest that a combination of abiotic factors (i.e. temperature) and biotic factors (i.e. food quality and food abundance) is responsible for latitudinal body size variation in animals, instead of one mechanism (i.e. heat conservation). This is supported by the fact that latitude alone is not the explanation for body size variation among latitudes, but that a combination of factors, i.e. temperature and precipitation, drives latitudinal body size variation. Therefore I encourage further studies to look at the interaction between abiotic and biotic factors to explain the mechanism behind Bergmann‟s rule, in which it is important to investigate the effects of global warming on vegetation types and the direct and indirect effects on food quality and food abundance.