Distribution of Pocket Gophers in Southeastern Colorado

Biogeographic relationships of the plains pocket gopher (Geomys bursarius), yellow-faced pocket gopher (Cratogeomys castanops), northern pocket gopher (Thomomys talpoides), and Botta's pocket gopher (T. bottae) were studied in southeastern Colorado. Extensive field investigations revealed that T. bottae and C. castanops are sympatric in an area of approximately 1000 km2, T. talpoides is allopatric with T. bottae and C. castanops, and G. bursarius is parapatric with C. castanops, T. bottae, and T. talpoides. Burrow depths, soi1 textures, and geographic distributions of the four species were analyzed statistically. Significant differences in depths of burrows were found except between T. bottae and the sympatric C. castanops and between T. bottae and the allopatric T. talpoides. Differences in the depths of burrows of sympatric pocket gophers probably do not prevent interspecific contact. G. bursarius generally is restricted to sandy or disturbed loamy soils, C. castanops and T. bottae are associated with compact rangeland soils, and T. talpoides inhabits well-drained, upland soils. However, the extent of overlap, as shown by textural analysis, indicates that partitioning of the soil resource doubtfully has occurred. Overall distributions of the four species differ significantly, but paired comparisons revealed that the distributions of T. bottae and C. castanops in south eastern Colorado do not differ significantly. Based on these data, it seems unlikely that competitive exclusion is alone or even primarily responsible for the distributional patterns of pocket gophers in southeastern Colorado. Rather, the distributions of pocket gophers probably are influenced primarily by environmental and historical factors.