Christian, D.P. 1993. Distribution and abundance of bog lemmings (Synaptomys cooperi and S. borealis) and associated small mammals in lowland habitats in northern Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 29+ pp.
There were four objectives to this study: 1) survey Chippewa National Forest to document the occurrence and habitat associations of species, 2) recommend whether species should retain their status as "Sensitive" species on the Chippewa National Forest, 3) sample three habitats--grass-sedge meadows, heath bogs, and lowland conifer forests--in ways that allow comparison of relative abundance and composition of small-mammal communities inhabiting each, and 4) further understanding of habitat distribution of small mammal species inhabiting these lowland habitats. Study sites were selected to maximize possibilities of capturing Synaptomys borealis and Phenacomys intermedius.
A total of 591 small mammals was captured during the study, including 5 star-nosed moles (Condylura cristata), 338 shrews representing five species (Sorex arcticus, S. cinereus, S. hoyi, S. palustris, and Blarina brevicauda), and 248 rodents representing 6 species (Microtus pennsylvanicus, Clethrionomys gapperi, Synaptomys cooperi, Synaptomys borealis, Peromyscus maniculatus, and Zapus hudsonius. The captures for Synaptomys borealis represent only the 6th locality record for this species in Minnesota, and the 1st record south of the extreme northern tier of counties in the state. This record also is the southernmost locality record for this species in midwestern North America, and is the first documentation of the presence of this species within the boundaries of the CNF. In the present study, S. borealis and S. cooperi were trapped in the same forest stand. The occurrence of four species of arvicoline rodents in a single habitat, as at the site of capture for S. borealis, is unusual and suggests the possibility of a potentially formidable array of interspecific interactions that may affect the distribution of S. borealis, S. cooperi, or both. It is possible that annual fluctuations in abundance of Clethrionomys gapperi affect habitat occupancy by Synaptomys in different years. In this study, both S. arcticus and M. pennsylvanicus were strongly associated with graminoid-dominated habitats (grass-sedge meadows); the tendency for these species to be associated with Synaptomys in heath bogs and lowland conifers provides indirect evidence for a positive relationship between Synaptomys and graminoids. Sites where Synaptomys was captured were characterized by relatively high numbers of shrews and of individual small mammals. This suggests that occupancy of heath or lowland conifer habitats by bog lemmings is not merely random. The presence of other small mammal species may be a direct factor, or may reflect vegetative or other habitat factors that also affect bog lemmings. Sorex arcticus was significantly more abundant in grass-sedge meadows than in the other two habitats and tended to be associated with M. pennsylvanicus in heath and conifer habitats. Zapus hudsonius has been found in a wide variety of habitats, and its occurrence only in grass-sedge meadows in the present study is surprising. S. cinereus was equally abundant in heath bogs and lowland conifer forests, but was significantly less abundant in grass-sedge meadows. These results suggest strong selection for habitats with ground vegetation dominated by ericaceous shrubs rather than grasses and sedges. S. hoyi was absent from grass-sedge meadows and was found only in heath bogs and lowland conifer forests, conforming closely to the pattern of habitat selection described by Brown (1967) for this species in the Rocky Mountains.
In this study, there was striking similarity among heath bogs, lowland conifer forests, and grass-sedge meadows in the number of individual small mammals, rodents, shrews, and small mammal species captured. This result suggests that, despite differences in vegetation structure and in small-mammal species composition, these 3 communities may be broadly similar in terms of aspects of ecosystem function involving small mammals.