Pocket Gophers in Alfalfa Fields: Causes and Consequences of Habitat-Related Body Size Variation

Adult body size in pocket gophers depends on the rate of postnatal growth over the first 3 mo or so of life. This growth rate, however, is strongly influenced by the nutritional quality of the available food. As a consequence, a considerable component of the enormous range in size among pocket gopher populations may result from phenotypic responses to differences in habitat between localities. As we document, the size of the gopher cranium, for example, is largely a function of the animal's nutritional plane. Such nutritional differences, however, do not appear to affect shape aspects of the skull. It is argued that cranial shape, not overall size, is the important component in recognizing evolutionarily significant geographic units of pocket gopher species.