Adaptive geometry of burrow spacing in two pocket gopher populations.

The burrows of Thomomys bottae analyzed in northern Arizona represent a tremendous energetic investment and are used for almost all activities of the rodents throughout their lives. Burrow length, home range area, perimeter, and number of adjacent neighbors were significantly higher for reproductive males than for females or nonreproductive males in the population. Spacing within and between individual burrow systems was uniform for all sizes and both sexes. Reproductive male pocket gophers relate to their neighbors in such a way as to increase the contact with potential mates, while all individuals, regardless of sex or reproductive condition, develop and maintain uniform internal spacing distances that are perhaps related to resource management. Males practice serial monogamy; instances were found of males and females sharing a common, deep nest between their individual burrows. This suggests a potential for parental care by males. Differences in plant production are possibly compensated for by altering burrow length rather than altering spacing. Plant production was approximately twice as great at one site as at the other. At the site of higher production, average burrow lengths were almost exactly one half those at the site of lower production. However, all values for spacing within and between individual burrow systems were statistically indistinguishable between the study sites. For both sites, the difference in burrow lengths appears to be attained by the addition of basic building units to a burrow, consisting of equal branch lengths and equal distances between branching points along a burrow. -from Authors