Interactions of Peromyscus and Mus in a One‐Acre Field Enclosure

Abstract

Peromyscus polionotus (old—field mice) and feral Mus musculus (house mice) have coexisted in a large old—field area at the AEC Savannah River Plant for 12 yr following removal of human habitations and the abandonment of agriculture in the region, but in two replicate experiments a Mus population has failed to survive when the two species were confined to a one—acre enclosure in the field. In the second experiment, as described in this paper, five Mus were introduced into the enclosure in December 1960 and nine Peromyscus in June 1961. Rapid population growth in both species occurred in the fall of 1961 until about 23 of each species were present, a much bigger density than occurred outside the enclosure. A decline in recruitment rate and a continued high disappearance rate in the Mus population resulted in a gradual decline and extinction of this species; whereas the Peromyscus population maintained itself at a level of 20 to 28 individuals. The two species at first occupied separate areas in the enclosure, but common occupancy of feeding areas increased as the density increased. It was concluded that interspecific competition for seeds was important in the outcome of the experiment, and that the migratory behavior of Mus greatly reduces competition with the more sedentary Peromyscus when populations of the two species are not confined to a limited area.