Fig. 3: Graphs showing the distribution of distances between stations at which mice were captured on successive nights in Mesa Verde National Park. Graphs for each species represent records of both males and females.
Individuals of P. truei and P. maniculatus usually do not have mutually exclusive home ranges. When the home ranges for all females or males of one species are drawn on a single map of the trapping grid, almost every one of their ranges overlaps with the range of at least one other mouse. In some instances, the home range of an individual overlaps ranges of several other individuals. In extreme cases an animal's range lies completely within the estimated boundaries of another individual's range. Such an enclosed range was always that of a juvenile or of a young animal. However, an adult may have more than half of its range overlapping with that of another adult of the same sex and of the same, or different, species.
In general, the two species tended to be restricted to certain areas of the trapping grid where the respective habitats were more favorable for their needs. [Figure 4] shows the parts of the trapping grid utilized by each species. Of course there is overlap in the areas utilized by each species; a few individuals of P. maniculatus may be found in what appears to be P. truei habitat, and vice versa. In such cases, an inspection of the vegetation usually reveals an intermediate type of habitat—for example, an open sagebrush area in pinyon-juniper woodland—that is habitable for either or both species.
The ranges of P. truei tend to be clustered in the western half of the trapping grid, where ranges of P. maniculatus are clustered in the eastern half of the grid ([Fig. 4]). The vegetation of the grid and the preferred habitats of each species are discussed in following chapters.
On the basis of the sizes of estimated home ranges, it is possible to compute the approximate number of individuals of each species that occur in each acre of appropriate habitat.
Fig. 4: Diagram of trapping grid south of Far View Ruins, showing the preferred habitats of P. truei and P. maniculatus.
On the basis of an average home range of 30,206 ± 25,545 square feet (one standard deviation) for both male and female individuals of P. truei, there should be approximately 0.781 to 9.345 individuals of this species per acre of pinyon-juniper woodland. An average home range of 29,400 ± 24,570 square feet for males and females of P. maniculatus indicates that the density of this species is between 0.807 and 9.018 animals per acre in mixed shrub or shrub and sagebrush types of vegetation.
[Figure 4] shows that approximately 10 of the 16 units of the trapping grid are suitable habitat for P. truei; the remaining six units are habitat of P. maniculatus. From the preceding calculations of density one could expect to find between seven and 90 individuals of P. truei, and between five and 54 individuals of P. maniculatus as residents within the 22.95 acres of the trapping grid. The higher estimates of density appear to be large enough to compensate for any overlapping of home ranges.