A statistically based study of the ecological factors influencing the local distribution of two subspecies of pocket gophers

The present paper deals with the contiguity of the ranges of Thomomys bottae pascalis and Thomomys bottae mewa north and east of Clovis, Fresno County, California. In this part of California, the pocket gopher of sierra foothills belongs to the race mewa, whereas the San Joaquin Valley is, in this region, occupied by pascalis, except that mewa also comes out into the valley about 3 miles distant from the nearest foothills. Ingles (1950) pointed out that the zone where intergradation occurs between these races may be as 4 miles wide, but emphasized that his data were inadequate to give an accurate estimate. He further stated that there was no visible reason why the intergrading zone should occur where it did. In order to obtain a better understanding of these and related problems it was decided to locate and map accurately, with respect to established landmarks, the zone of intergradation from Collins Corner and the Enterprise Canal, where intergrades were previously found (Ingles, 1950) to the place where the intergrading zone crossed Maple Road, about ten miles to the northwest (see map, figure 1). An attempt was made to determine the physical and biological factors affecting the present position of the line of contiguity between the two ranges.