One possible explanation for this positive latitude versus size relationship is
Bergmann's rule (Bergmann 1847), which relates this type of size increase in endotherms to a heat conservation mechanism: the larger the animal, the better it can conserve heat in the colder northern latitudes.
This study shows that: 1) the age differs significantly among the six populations of Boana cordobae, and as morphometric variables positively correlates to age, this age differences can partly explain the geographic variation of morphometric variables; 2) age-adjusted morphometric variables allow that differences among sites became more significant; 3) the patterns of variation in age and morphometric variables are related with the climate, and therefore this could be related to
Bergmann's rule.
2014:
Bergmann's rule for Neomys fodiens in the middle of the distribution range.
Bergmann's Rule generally holds true for whitetail deer.
In the present paper, we deal with
Bergmann's rule. As in Romero et al.
Volynchik [19], however, found that a large-bodied local viper (Vipera palaestinae), with a Mediterranean distribution pattern, does not follow
Bergmann's rule or its converse.
Conformity to
Bergmann's rule in the Plateau pika (Ochotona curzoniae Hodgson, 1857) on the Qinghai-Tibetan Plateau.
While
Bergmann's Rule explains how animals deal with issues of heat loss and heat regulation in the cold, there may be other reasons to pack more pounds in colder climates.
Geographic gradients in body size: a clarification of
Bergmann's rule. Diversity and Distributions 5:165-174.
For example, on the basis of
Bergmann's rule (below), Van Bushirk et al.
Amphibians do not follow
Bergmann's rule. Evolution, 62:413-420.
In its classical sense,
Bergmann's rule (Bergmann 1847) proposed that homeothermic animals display size clines; species within a genus are larger in cooler climates and smaller in warmer climates because of selection on the ability to thermoregulate (Bergmann 1847, James 1970, Blackburn et al.