Dispersion Patterns of Mice in California Annual Grassland

Dispersion patterns of grassland mice were contagious. The frequency of occurrence of Microtus californicus tracks and pooled tracks of Pero-myscus maniculatus and Reithrodontomys megalotis showed positive correlations with the per cent cover of wild oats {Avena). No such correlations existed with other widespread species of grass nor with the total amount of grass cover. The distribution of cuttings suggested that Avena was the major food of Microtus at this time thus implicating food as a major factor in the control of dispersion. Trapping records revealed seasonal changes in the concentrations of mice on different parts of the study plot. The concentration of Microtus was inversely related to the concentration of the other species, which suggested that dispersion was influenced by interspecific interactions.