The Effects of a Successional Habitat Mosaic On a Small Mammal Community

Abstract

Small herbivorous mammals living in successional patchy environments may be affected by both patch size variations and successional changes. If patch size affects densities of residents then larger patches should have higher densities compared to smaller patches because larger patches often have greater habitat diversity and lesser chances of stochastic events destroying the population. If patch size affects length of time animals spend on patches (persistence rates) then smaller patches should have lower persistence rates compared to larger patches because smaller patches contain fewer resources. Larger animals may be constrained by body size, as well as population size, to reside only on the larger patches because smaller patches do not contain enough resources. If successional changes affect resident animals that are host specific on colonizing plant species, then the effects may be noticeable immediately following field abandonment because plant species replacement rates are most rapid then. Four small mammal species were included: Sigmodon hispidus, Reithrodontomys megalotis, Microtus ochrogaster, and Peromyscus maniculatus. The field was divided into patches that varied in area by two orders of magnitude with patches of each size treatment placed in each section of the field. Patch size effects on densities and persistence rates of the four mammal species were tested with analyses of variance. Plant species were grouped according to seven life history traits so as to include relative percent cover of most plant species. Multiple linear regression analyses were used to identify which variables (patch size, field sections, and percent relative cover) significantly explained variations in small mammal densities. Effects of patch size on animal densities and persistence rates varied among animal species. The largest species, Sigmodon hispidus, was never found on the smallest patches, but densities of Reithrodontomys magalotis, Microtus ochrogaster, and Peromyscus maniculatus were often highest on the smallest patches. Animal density variations were often significantly explained by patch size using multiple regression analyses (P ≤ .001). However, lack of consistent trends with respect to the other independent variables included in the equations and variable R2 values suggested that other, unmeasured, variables may have influenced the results. Persistence rates of the three species were often highest on the largest patches. Results suggested that animals visited small patches more often than large patches without staying, and used large patches to create territories. Small and medium patches may have been used as archipelagos of preferred habitat interspersed with less desirable habitat. The first stage of old—field succession was completed by the end of the 3rd yr: perennials replaced annuals as the dominant plant species. Neither patch size nor field sections significantly affected percent cover.