High Prevalence of Borrelia mayonii (Spirochaetales: Spirochaetaceae) in Field-Caught Tamias striatus (Rodentia: Sciuridae) From Northern Wisconsin

Borrelia mayonii is a recently discovered bacterial spirochete that causes Lyme disease and is transmitted by the blacklegged tick, Ixodes scapularis Say (Acari: Ixodidae). To date, B. mayonii has been isolated from two vertebrate host species in Minnesota: field-caught white-footed mice (Peromyscus leucopus Rafinesque; Rodentia: Cricetidae) and American red squirrel (Tamiasciurus hudsonicus Erxleben). Here, we describe the first detection of B. mayonii in field-caught eastern chipmunks (Tamias striatus L. (Rodentia: Cricetidae)) from northern Wisconsin. During our study, we captured 530 unique small mammals and found an infection prevalence of 23.50% in field-caught eastern chipmunks (4/17) and 1.19% in Peromyscus spp. (5/420). Mean larval and nymphal burdens were determined for captured Blarina brevicauda (0, 0), Glaucomys volans (0.29, 0.14), Myodes gapperi (0.27, 0), Napaeozapus insignis (0, 0.25), Peromyscus spp. (1.88, 0.11), T. striatus (1.06, 0.65), and Sorex cinereus (0.09, 0). The high B. mayonii infection prevalence in eastern chipmunks suggests that the species may be an important reservoir for B. mayonii in the Upper Midwest.

Examining Interspecific density-dependent dispersal in forest small mammals

The effects of conspecific densities on dispersal have been well documented. However, while positive and negative density-dependent dispersal based on conspecific densities are often shown to be the result of intraspecific competition or facilitation respectively, the effects of heterospecific densities on dispersal are examined far less frequently. This despite the potential for the analogous processes of interspecific competition and heterospecific attraction to influence dispersal. Here we use 51 years of live-trapping data on deer mouse (Peromsycus maniculatus), eastern chipmunk (Tamias striatus), red-backed vole (Myodes gapperi), and jumping mice (Napaeozapus insignis and Zapus hudsonius) to examine the effects of both conspecific and heterospecific densities on dispersal frequency. In terms of conspecific densities, jumping mice were more likely to disperse from areas of low conspecific densities, while red-backed voles and chipmunks did not respond to conspecific densities in their dispersal frequencies. When considering interspecific density effects, while there were no statistically clear effects of density on dispersal frequency, the effects of chipmunk and jumping mice densities on dispersal by red-backed vole were greater than the effects of conspecific densities, with voles more likely to disperse from areas of high chipmunk densities and low jumping mice densities. Likewise, the effect of chipmunk densities on dispersal by jumping mice was greater than the conspecific density effect. Conspecific densities clearly can affect dispersal by two of these four species, but the effects of heterospecific densities on dispersal frequency are less clear. Based on effect sizes it appears that there is potential for heterospecific effects on dispersal by some species in the community, but future experimental work could elucidate the strength and causes of these relationships.

The short-term impact of abundant fruit upon deer mouse (Peromyscus maniculatus), southern red-backed vole (Myodes gapperi), and woodland jumping mouse (Napaeozapus insignis) populations

Fruit has been identified as an important and potentially population-restricting food for southern red-backed voles (Myodes gapperi (Vigors, 1830)), deer mice (Peromyscus maniculatus (Wagner, 1845)), and woodland jumping mice (Napaeozapus insignis (Miller, 1891)). We added domestic dried strawberries (Fragaria × ananassa (Weston) Duchesne ex Rozier (pro sp.)) and European black currants (Ribes nigrum L.), which have native analogues and are preferred foods of these rodents, to white spruce (Picea glauca (Moench) Voss) plantations from May through August 2011 and 2012 to test fruit and fruit-based carbohydrate’s short-term (1–2 years) impact on these rodent populations. We used mark–recapture to estimate density, percentages of population that were juvenile and breeding female, mean home-range size, and body mass during spring and summer of both years, and fecundity via placental scars from euthanized females in summer 2012. Fruit enhancement had no apparent effect on our species’ fecundity, proportion of breeding females or juveniles during spring and summer of either year, nor were there differences among these metrics in spring 2012 following 2011 fruit additions. Overall, there were no impacts to the short-term adult population dynamics for any species during fruit addition. We are led to believe that short-term pulses of fruit and (or) fruit-based carbohydrate abundance do little to influence temperate forest small-mammal populations.

Does fungus consumption by the woodland jumping mouse vary with habitat type or the abundance of other small mammals?

Fungi are important in the diet of many small mammal species, but patterns of fungus consumption (mycophagy) in eastern forests of North America have received little attention. Examination of stomach contents of the woodland jumping mouse, Napaeozapus insignis, revealed that fungi were an important dietary component in both eastern hemlock and mixed mesophytic habitats. Jumping mice in both forest types consumed mostly Glomalean fungi (primarily from the genera Glomus and Endogone), in agreement with previous studies. Mice also consumed fungi from the genera Elaphomyces and Melanogaster, previously unreported in the literature. Fungi from the genus Hymenogaster were only found in mice from eastern hemlock habitats. Melanogaster spores occurred more frequently in jumping mice from sites in which deer mice, Peromyscus maniculatus, were abundant, whereas Glomalean fungi were less frequent in the diet of N. insignis when deer mice were abundant. Overall frequency of spores in the diet of jumping mice was negatively related to the abundance of deer mice, suggesting that interactions between species may shape patterns of mycophagy.

The spatial component of variation in small-mammal abundance measured at three scales

We studied small-mammal populations across a range of spatial scales to determine if they exhibited spatial variability that was independent of the distribution of vegetation. Between 1996 and 1999, systematic livetrapping surveys were conducted on nested grids at three scales: (1) extent (total area covered by a grid) = 4900 ha, grain (minimum space between sampling points) = 1000 m; (2) extent = 306 ha, grain = 250 m; and (3) extent = 31 ha, grain = 125 m. The four most abundant species were the red-backed vole (Clethrionomys gapperi), the short-tailed shrew (Blarina brevicauda), the deer mouse (Peromyscus maniculatus), and the woodland jumping mouse (Napaeozapus insignis). Small mammals exhibited spatial population structure over distances up to 250 m but not over 1000 m. There was a component of this population structure that appeared to be temporally and spatially dynamic, and that was not correlated with measured vegetation variables. We discuss processes that would create the observed metapopulation structure in seasonal landscapes.

An experimental test of habitat selection by rodents of Algonquin Park

Using an enclosure experiment, we tested whether substrate selection by deer mice (Peromyscus maniculatus), redback voles (Clethrionomys gapperi), and woodland jumping mice (Napaeozapus insignis) matched habitat-use patterns determined from trapping data. Mice were introduced into a 5 m diameter enclosure containing substrates from three habitats: maple, mixed, and coniferous forest. Trapping data were taken from a long-term monitoring study of small-mammal populations in Algonquin Park, Ontario. We used data from 1991 – 1995 from the three habitats used in the enclosure experiment. If competition or predation affects habitat distribution patterns, then, given a choice, mice should select different substrates in the enclosures from those they use in the field. Alternatively, if habitat use is not constrained by interactions with competitors or predators (i.e., if small mammals select habitats), then habitats used in the enclosure should match habitat distributions observed in the field. Habitats used in the field did not match habitats selected in the enclosure experiment for either deer mice or woodland jumping mice. Redback voles selected habitats similar to those used in the field. We conclude that interspecific competition and (or) predation may limit availability of habitats for deer mice and woodland jumping mice.

Relative abundance, richness, and diversity of small mammals at induced forest edges

To determine whether small mammals show "edge effect" at induced forest edges created by harvest cutting, small mammals were snap-trapped from 1990 to 1992 at 5 sites harvested 0–10 years previously in the University of New Brunswick Forest, Fredericton. Nine species were captured in 8686 trap-nights. There was edge effect in older (6–10 years) but not in recent (0–5 years) cuts. This was shown by both high relative abundance for all species combined and species diversity in the ecotone (from 10 m into the harvest cut to 10 m into the forest). Species richness did not show any edge-related pattern. Edge effect with respect to relative abundance was largely due to Peromyscus maniculatus and Clethrionomys gapperi. Peromyscus maniculatus reached the highest relative abundance 10 m in the forest and was not captured beyond 10 m in the harvest cut. Clethrionomys gapperi made use of the forest side of the ecotone and was not captured beyond 5 m in the harvest cut. Napaeozapus insignis, Zapus hudsonius, and Soricidae (Blarina brevicauda, Sorex cinereus, and S. fumeus) showed no attraction to, or avoidance of, the edge.