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Habitat use by small mammals in the Southwestern Yukon : the role of competitive interactions Galindo, Carlos


Many species of small mammals live in the southwestern Yukon. Most of them live in different habitats or overlap very little. However, their use of habitats changes as their populations fluctuate. In this study I investigated how far competitive interactions influence the use of habitats and relative abundance of the common species of mice. I worked in two ecotones. First, the ecotone between alpine meadows and subalpine shrub tundra. Here, populations of singing voles (Microtus miurus) and tundra voles (M. oeconomus) living in each habitat respectively, overlap little. Second, the ecotone between boreal forest and sedge meadow. Here, populations of deer mouse (Peromyscus maniculatus) and red-backed vole (Clethrionomys rutilus) inhabiting the forest, meet with meadow voles (M. pennsylvanicus) living in the sedge meadows. If interspecific competition is influencing the habitat use and relative abundance of these species, then removal of one of them will change habitat use and abundance of the remaining species. In the first field season, I removed tundra voles to look at the effect on the contiguous population of singing voles. Similarly, I removed meadow voles to look at the effect on the contiguous population of deer mouse. In both places I used an experimental and a control live-trapping grid. In both cases the removal of one species had no effect on the other species' distribution or demography. In the second field season, singing voles and tundra voles disappeared from the area. Meadow voles, in turn, declined to very low numbers and I used their natural fluctuation as a removal experiment. Deer mouse populations were not affected even when the natural decline of meadow voles was more effective on maintaining the seadge meadow free of voles than the previous removal manipulation was. In the third year, meadow voles colonized two areas of forest where deer mice had been alone the previous two field seasons. Red-backed voles, in turn, increased from very low numbers in four grids. To look at the effect of meadow voles on deer mice I examined the spatial distribution and abundance of the latter species in areas where voles were absent as well as in the same places during previous years. To look at the effect of red-backed voles on deer mice, I examined the spatial distribution and numbers of the latter species in places with low and high densities of red-backed voles. Neither meadow voles nor red-backed voles affected the spatial distribution or abundance of deer mice. The results of this study indicate that competitive interactions have no influence on the use of habitats and relative abundance of the common species of small mammal species in the area. However, as it is evident from this study, populations of small mammals in the area are extremely dynamic. Some years they are scarce and some others they are abundant. Since competitive interactions may change as density increases, the conclusions of this study are restricted to the densities at which I found their populations.

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