Conformity to Bergmann's rule in the plateau pika (Ochotona curzoniae Hodgson, 1857) on the Qinghai-Tibetan Plateau

Interspecific and intraspecific variation in the body sizes of warm-blooded animals is usually correlated with geographical gradients (latitude and/or altitude) according to the well-known Bergmann's rule. However, what determines conformity to Bergmann's rule or even whether this rule is valid has been debated. We tested the relationships between skull size of the plateau pika (Ochotona curzoniae) collected from different geographic localities and two geographic variables (latitude and altitude) as well as some environmental factors that usually change with geographical gradients on the Qinghai-Tibetan Plateau. Our results indicated that skull size was positively correlated with both latitude and altitude, and negatively correlated with annual temperature, annual precipitation, and annual net primary production. These results indicated conformity to Bergmann's rule in this species, i.e., the body size of the plateau pika tends to increase with climate severity and food scarcity.