Effects of Vegetation, Landscape Composition, and Edge
Habitat on Small-Mammal Communities in Northern
Massachusetts
Eric S. Lindemann, Jonathan P. Harris, and Gregory S. Keller
Northeastern Naturalist, Volume 22, Issue 2 (2015): 287–298
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2015 NORTHEASTERN NATURALIST 22(2):287–298
Effects of Vegetation, Landscape Composition, and Edge
Habitat on Small-Mammal Communities in Northern
Massachusetts
Eric S. Lindemann1, Jonathan P. Harris1, and Gregory S. Keller1,*
Abstract - In southern New England forests, small mammals provide essential contributions
to ecosystem functioning via food-web interactions and seed dispersal. This region
has been exposed to extensive habitat fragmentation due to residential and agricultural development,
resulting in a considerable amount of edge habitat, in addition to naturally
occurring landscape heterogeneity. Limited research has been conducted relating smallmammal
species richness and abundance to different types of edge habitat in this region.
Studies incorporating an analysis of variation in both fine-scale vegetation and coarse-scale
landscape variation are even more limited. We compared small-mammal richness, total
abundance, and abundance of Peromyscus maniculatus (Deer Mouse), Peromyscus leucopus
(White-footed Mouse), Myodes gapperi (Red-backed Vole), Tamias striatus (Eastern
Chipmunk), and Tamiasciurus hudsonicus (Eastern Red Squirrel) at developed-edge, wetland-
edge, and forest-interior sites. We also measured vegetation and landscape variables to
understand how variation in characteristics at different scales affected small-mammal measures.
We selected 4 sites of each edge type and used Sherman live-traps during the
summers of 2009–2010 to survey small-mammal populations (75 traps for 4 nights at 12
sites for 2 y = 7200 trap-nights). We did not find differences among edge types and interior
forest for total abundance, richness, and abundance of the 5 small-mammal species with
sufficient data for analysis. However, vegetation variables and landscape variables were
significantly associated with small-mammal populations. Step-wise linear regression included
vegetation variables for 4 of the 5 species, and various landscape scales were
included in all analyses except abundance of Peromyscus adults. Patch size was included in
4 analyses (positive for total abundance, White-footed Mouse, and Red-backed Vole; negative
for Eastern Chipmunk). We found conifer basal area to have a positive relationship with
abundance of Peromyscus adults and Red-backed Voles, but a negative relationship
with abundance of Peromyscus juveniles and Eastern Red Squirrels. Species abundance and
richness of small-mammal communities and populations in northeastern Massachusetts
were related to both fine-scale vegetation differences and coarse-scale landscape metrics,
but these relationships were complex and scale-dependent.
Introduction
Residential and agricultural development in southern New England has fragmented
forests, resulting in more developed edges, less interior forest, and less
habitat for area-sensitive and forest-interior species (Yahner 2000). In northern
Massachusetts, forests are heavily fragmented by both historic agricultural
development and current residential development. Edge creation from forest
1Department of Biology, Gordon College, Wenham MA 01984. *Corresponding author -
greg.keller@gordon.edu.
Manuscript Editor: Rosalind Renfrew
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fragmentation results in increased sunlight penetration, more shrub-level and understory
cover, and different food resources compared to the forest interior (Yahner
2000). Although edge habitats may appear similar, Yahner (1988) has suggested that
they are not identical and require further study.
Small mammals are important biological components of forest communities:
they play a vital role in food-web interactions and as seed dispersers (e.g.,
Schmidt et al. 2001, Swengel and Swengel 1992, Verme 1957). Small-mammal
populations may be negatively impacted by habitat fragmentation, which affects
their movement patterns (Diffendorfer et al. 1995), foraging strategies (Orrock
and Danielson 2005), population structure (Nupp and Swihart 2000), and reproductive
output (Wilder and Meikle 2006). In turn, these impacts can alter species
richness and abundance, community-level interactions, and food-web dynamics in
the forests of Massachusetts.
While extensive fragmentation effects may reduce small-mammal populations,
influences are likely species specific, and resultant patterns may counter
this more general reduction trend. For example, Nupp and Swihart (2000) found
that although species richness was lower in smaller forest patches, abundance of
Peromyscus leucopus (White-footed Mouse), a species they note to be commonly
considered a habitat generalist and more abundant in smaller forest-patches, was
not related to patch size. In Pennsylvania, Yahner (1992) found that abundance
of White-footed Mice actually increased as fragmentation increased. Yahner also
noted that abundance of Myodes gapperi (Red-backed Vole) was not associated
with degree of fragmentation.
Differences in habitat use based on edge type provide an additional consideration
of fragmentation for these species. For example, Bayne and Hobson (1998) found
that the types of habitat surrounding patches affected small-mammal abundance in
agricultural edges but not silvicutural edges. They also reported that Peromyscus
maniculatus (Deer Mouse) were more abundant in edge habitats compared to interior
habitats. In contrast, in the highly fragmented region of east-central Illinois,
Wolf and Baltzi (2002, 2004) found that White-footed Mouse was more abundant
in forest-interior habitat compared to edges. These studies illustrate that habitat
fragmentation results in varied patterns that are species specific and require both
community-level and population-level analyses.
In this study, we used live trapping to study the effects of fragmentation and
natural landscape heterogeneity at multiple scales on small-mammal communities
and populations. Our objectives were to: (1) compare differences in small-mammal
richness, total abundance, and abundance of individual species at developed-edge,
wetland-edge, and forest-interior habitats; and (2) determine how differences in vegetation
structure and landscape-level fragmentation affected richness and abundance.
Methods
This study was part of a larger project on the effects of edge characteristics on terrestrial
vertebrates in New England. Study areas were in public forests at Appleton
Farms, Agassiz Rock Wilderness Area, Gordon College, and Long Hill Reservation
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in northern Essex County, MA. Sites were located within a 65-km2 area (center
= 42.616997°N, 70.820145°W). Forests in this region are dominated by Quercus
spp. (oak), Carya spp. (hickory), Pinus strobus L. (Eastern White Pine), with some
Acer rubrum L. (Red Maple), Fagus grandifolia (Ehrh.) (American Beech), Tsuga
canadensis (L.) Carr. (Eastern Hemlock), and Betula spp. (birch). We selected sites
that were similar in vegetation, and gave preference to areas with oak and hickory
overstory trees because of their potential importance as food resources. The region
contains 48% forest, with numerous small ponds and vernal pools, emergent wetlands,
extensive pasture and horse farms, and both historic and recent residential
development.
We selected 3 habitat categories for study: developed edge (forest abutting agricultural
and residential development), natural-wetland edge (forest abutting wetland),
and forest-interior habitat. Edge sites were in forest habitat centered within 20 m of
the edge–canopy opening; interior sites were located at least 150 m from an edge.
This distance, selected for a separate analysis of edge effects on avian communities,
is greater than what is typically defined as interior forest for small mammals (Bayne
and Hobson 1998, Mills 1995, Pardini 2004). Sites were at least 300 m apart to ensure
independence. We selected 4 sites for each category, identified using ArcGIS
9.3 software and ground-truthing.
We trapped small mammals between 30 May and 5 July in 2009 and 2010. At
each site, we used 75 Sherman live-traps for 4 consecutive nights (Nupp and Swihart
2000), resulting in a total of 600 trap-nights per site and 7200 trap-nights total.
We grouped sites that were spatially close to each other and randomly selected the
order of trapping for each group. Within a group, we systematically ordered our
trapping effort, and made sure that we trapped in sites from more than one habitat
category at the same time to avoid temporal bias. Traps were set at 2–3 sites concurrently.
At each site, we set 3 rows of 25 traps with traps ~3 m from adjacent traps.
We baited traps with rolled oats mixed with peanut butter, provisioned them with
cotton balls for warmth and cover, and checked them every morning. We marked
individuals with ear tags; determined species, gender, and breeding condition; and
recorded tail, body, ear, and foot length (Oxely et al. 1974). Repeat captures were
not counted in survey totals. We released individuals at the point of capture immediately
after processing and we collected any dead individuals as vouchers and
submitted them to the Gordon College Museum of Natural History, Wenham, MA.
We collected vegetation data during June–July 2009 at each site following a
modified version of James and Shugart’s (1970) methods. In an attempt to reduce
the number of correlated variables, we limited the large number of potential
variables to those that might have biological significance to small mammals. Species
composition of understory and overstory trees and shrubs were qualitatively
similar among sites. We quantified vegetation within a 12-m radius circular plot
centered at each site; edge-sampling plots were located 15 m into the forest from
the edge. Within each plot, we counted the number of snags (>7.5 cm diameter at
breast height [dbh], >1.5 m tall) and logs (>7.5 cm dbh, >25 cm long). We counted
the number of overstory trees (>7.5 cm dbh, >1.5 m tall) and measured dbh of
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coniferous and deciduous overstory trees to calculate total basal area separately for
the 2 types. We counted the number of understory trees (<7.5 cm dbh, >1.5 m tall)
and shrubs (less than 7.5 cm dbh, 0.5–1.5 m tall) along a 1 m x 12 m transect in each of
the 4 cardinal directions from the center of the plot and measured percent leaf litter,
percent herbaceous cover, and percent canopy cover with an ocular tube at 2-m
intervals along the same transects, for a total of 20 points per plot.
Using 2008 digital ortho quarterquads (DOQQs) from the Massachusetts Office
of Geographic Information (http://www.mass.gov/mgis/massgis.htm), we calculated
landscape metrics in ArcMap 9.3 (Environmental Systems Rsearch Institute,
http://www.esri.com). We outlined circles 200, 500, and 1000 m from the center of
each study site within which we delineated patches of forest and lengths of edges.
We used the editing and measuring tools to outline feature classes and determine
the extent of forest cover within each circle. We measured the total amount of forest
(ha), total linear length (m) of developed edge, and total linear length (m) of
wetland edge. We also outlined and calculated the forest-patch size in which study
sites were located, defined as contiguous forest without breaks from roadways,
power-line rights-of-way, or other natural or human-created openings.
Analysis
We compared vegetation variables, landscape variables, and mammal richness
and abundance using ANOVA and posthoc Tukey’s test of pairwise comparisons
for significant differences, with habitat categories (wetland edge, developed
edge, and forest interior), year, and year*habitat category interaction as the independent
variables. Dependent variables for mammal data included species
richness (number of species documented at each site), total abundance (number
of different individuals captured at each site for all species combined), and abundance
of individual species with at least 8 different captures during both years
combined. Given the difficulty of distinguishing the 2 Peromyscus species using
morphological data in the field (Choate 1973, Rich et al. 1996), we also combined
abundances of these 2 species to analyze at the genus level, and we analyzed
Peromyscus adults and juveniles separately. Years (year, year*habitat category)
were not significantly different from each other for all measures; therefore, we
combined data from both years for subsequent analyses.
We used forward stepwise regression (α = 0.15 to add or remove a variable) to
assess effects of landscape and vegetation variables on small-mammal richness and
abundance. Starting models included 4 independent landscape variables within each
of 3 radii (200 m, 500 m, and 1000 m) from the center of each study site: patch size,
percent forest, linear length of wetland edge, and linear length of developed edge.
Independent vegetation variables were: density of snags, logs, shrubs, understory
trees, overstory coniferous trees, and overstory deciduous trees; total basal area of
overstory coniferous trees and deciduous overstory trees; overstory tree richness;
and percent canopy cover, herbaceous ground cover; and leaf litter. For all analyses,
α = 0.05, and we report trends for 0.05 < P < 0.10. We analyzed data using Minitab
14 (2002; State College, PA).
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Results
Habitat categories differed in several vegetation and landscape metrics (Table 1).
On average, wetland-edge sites tended to have greater canopy cover and deciduous
basal area compared to other sites. Interior sites had greater tree richness, more deciduous
trees, snags, and logs, and larger patch sizes than other habitat categories.
Habitat categories differed at all landscape scales including 200-m developed edge
and forest, 500-m developed edge, and 1000-m wetland edge.
We captured a total of 9 small-mammal species during both years combined,
including 115 different individuals of 8 species during 2009 and 119 different
individuals of 8 species during 2010 (Table 2). Species with the highest number
of captures included Deer Mouse, White-footed Mouse, Red-backed Vole, Red
Squirrel (Tamiasciurus hudsonicus), and Eastern Chipmunk (Tamias striatus).
We did not capture enough Glaucomys volans (Southern Flying Squirrel), Blarina
Table 1. Average (± SE) values for vegetation and landscape metrics that differ significantly between
developed-edge, wetland-edge, and forest-interior site categories in northeastern Massachusetts
during the summers of 2009 and 2010. Values for habitats with different superscripted letters are
significantly different (P < 0.05) from each other based on ANOVA and Tukey’s test of pairwise
comparisons.
Variable Developed edge Wetland edge Forest interior
Tree richness (# species) 3.0 ± 0.5A 3.7 ± 0.2AB 4.8 ± 0.3B
Canopy cover (%) 88.8 ± 2.8A 98.3 ± 1.1B 96.3 ± 2.5AB
Deciduous density (# individuals) 9.8 ± 1.5A 13.0 ± 1.9AB 19.0 ± 2.3B
Deciduous basal area 8291.0 ± 1174AB 4003.0 ± 594B 12,190.0 ± 2056A
Snag density (# individuals) 2.0 ± 0.5A 2.0 ± 0.6A 5.0 ± 0.9B
Log density (# individuals) 4.5 ± 1.0A 7.5 ± 0.9AB 12.5 ± 3.0B
Patch size (ha) 16.4 ± 3.5A 89.1 ± 36.7A 117.4 ± 18.6B
Developed edge (m) within 200 m 661.0 ± 116A 148.0 ± 40B 224.0 ± 85B
Forest area (ha) within 200 m 8.3 ± 0.4A 10.4 ± 0.4A 6.8 ± 0.7B
Developed edge (m) within 500 m 5052.0 ± 490A 2015.0 ± 471B 2355.0 ± 492B
Wetland edge (m) within 1000 m 4557.0 ± 211A 6204.0 ± 520AB 7048.0 ± 972B
Table 2. Total number of new captures of each species documented during the summers of 2009/2010
in 3 habitat categories (developed edge, wetland edge, and forest interior; 4 sites within each type and
total of 7200 trap-nights) in northeastern Massachusetts.
Species Developed edge Wetland edge Forest interior
Blarina brevicauda Say (Short-tailed Shrew) 3/0 0/0 1/0
Sorex cinereus Kerr (Masked Shrew) 0/0 0/0 1/3
Peromyscus leucopus Rafinesque (White-footed Mouse) 4/4 11/11 5/14
Peromyscus maniculatus (Wagner) (Deer Mouse) 26/24 24/11 17/16
Peromyscus juveniles 13/13 12/9 8/10
Peromyscus adults 17/15 23/13 14/20
Myodes gapperi (Vigors) (Red-backed Vole) 2/0 8/11 2/2
Tamiasciurus hudsonicus Erxleben (Red Squirrel) 0/2 4/5 2/6
Tamias striatus L. (Eastern Chipmunk) 1/4 0/2 0/1
Glaucomys volans L. (Southern Flying Squirrel) 3/0 1/0 0/1
Mustela frenata Lichtenstein (Long-tailed Weasel) 0/0 0/1 0/0
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brevicauda (Northern Short-tailed Shrew), Sorex cinereus (Masked Shrew), or
Mustela frenata (Long-tailed Weasel) individuals to allow further species analyses.
We found no significant difference among the 3 habitat types for species richness
(F2, 21 = 0.03, P = 0.97) or total abundance (F2, 21 = 0.56; P = 0.58) (Fig. 1). Furthermore,
species-abundance patterns did not differ based on habitat type, although
the number of captures of White-footed Mouse averaged 2 individuals less and
Deer Mouse 2 individuals more at developed-edge sites compared to other habitats
(Fig. 2). Red-backed Voles were found almost exclusively at wetland-edge sites
(mean = 2.3 ± 1.3), but among-site variation was high.
Both vegetation and landscape characteristics were associated with smallmammal
variables (Table 3). Species richness and abundance were not associated
with vegetation metrics; however, abundance of 4 of the 5 species we analyzed
separately, as well as the composite Peromyscus adults and Peromyscus juveniles,
responded to vegetation measures. Abundance of Peromyscus adults and
Red-backed Voles were positively related to conifer basal area, Deer Mouse abundance
was higher where leaf litter was lower, and Eastern Chipmunk abundance
was lower where tree richness was higher. Eastern Red Squirrel abundance was
positively related to closed-canopy conditions with low shrub-density and low
coniferous basal area. Peromyscus juvenile abundance was positively related to
shrub density and conifer density; in contrast, Peromyscus adult abundance was
associated with lower conifer basal area.
Landscape-level metrics were included in regression models for each analysis
except Peromyscus adult abundance (Table 3). Patch size was positively associated
Figure 1. Average (+ SE) richness (P = 0.97) and abundance (P = 0.58) of small mammals at
4 developed-edge, 4 forest-interior, and 4 wetland-edge sites in northeastern Massachusetts
during summer 2009–2010 (years combined; total of 7200 trap-nights).
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Figure 2. Average (+ SE) abundance of Peromyscus leucopus (White-footed Mouse) (P =
0.11), Peromyscus maniculatus (Deer Mouse) (P = 0.42), Myodes gapperi (Red-backed
Vole) (P = 0.15), Tamias striatus (Eastern Chipmunk) (P = 0.19), and Tamiasciurus hudsonicus
(Eastern Red Squirrel) (P = 0.44) at 4 developed-edge, 4 forest-interior, and 4
wetland-edge sites during the summers of 2009 and 2010 (years combined; total of 7200
trap-nights). P-values illustrate results from ANOVA comparisons among habitats.
Table 3. Significant differences (P < 0.05) and trends (0.05 < P < 0.10) between small-mammal richness,
total abundance, and individual abundance relative to vegetation and landscape variables from
forward step-wise regression during the summers of 2009 and 2010 in northeastern Massachusetts.
The R2 value represents the overall regression equation. The - and + symbols before variables indicate
the direction—negative and positive, respectively—of the regression relationship.
Variable R2 Vegetation (P-value) Landscape (P-value)
Richness 19.7 - 500-m wetland edge (0.03)
Abundance 59.2 + Patch size (0.02)
- 200-m forest (0.02)
+ 500-m developed edge (0.004)
- 1000-m developed edge (0.04)
Peromyscus adults 16.0 + Conifer basal area (0.05)
Peromyscus juveniles 66.4 + Shrub density (0.004) + 500-m developed edge (0.08)
- Conifer basal area (0.007)
+ Conifer density (0.04)
P. leucopus 32.6 + Patch size (0.03)
+ 200-m wetland edge (0.05)
P. maniculatus 45.0 -% leaf litter (0.13) + 500-m developed edge (0.03)
+ 1000-m forest (0.02)
Myodes gapperi 96.1 - Deciduous density (less than 0.001) + Patch size (less than 0.001)
+ Conifer basal area (0.04) - 500-m wetland edge (0.03)
+ 500-m developed edge (0.004)
Tamias striatus 21.3 - Tree richness (0.12) - Patch size (0.06)
Tamiasciurus hudsonicus 53.0 + Canopy cover (0.007)
- Conifer basal area (0.03)
- Shrubs (0.07) - 200-m forest (0.001)
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with total abundance and White-footed Mouse and Red-backed Vole abundance, but
negatively associated with abundance of Eastern Chipmunk. Species-abundance
patterns illustrated associations with various scales of landscape-level metrics. For
example, White-footed Mice were associated more with wetland-edge habitat at
200 m, and Deer Mice and Peromyscus juveniles were more abundant when there
was more linear developed-edge within 500 m. Deer Mouse abundance was higher
where there was more forested area within 1000 m. Red-backed Vole abundance
was greater when there was more developed edge but lower when there was more
wetland edge within 500 m. Both total small-mammal and Eastern Red Squirrel
abundance were associated with less forest within 200 m.
Discussion
We expected that the natural heterogeneity and high productivity associated with
natural wetland edges would support greater richness and abundance of small mammals
compared to developed edges. Furthermore, we hypothesized that vegetation
differences associated with interior forest also would lead to greater richness and
abundance relative to developed edges. Our data, however, did not support these
hypotheses. We found evidence of community-level and population-level responses
to both coarse-scale (landscape) and fine-scale (vegetation) features. Richness,
total abundance, and White-footed Mouse and Red-backed Vole abundances were
negatively associated with landscape-level habitat fragmentation as measured by
patch size and amount of edge. However, patterns were diverse, and even seemingly
inconsistent; for example, we often found a positive response to fragmentation at 1
scale but a negative response at another scale.
Richness and abundance did not differ significantly among the 3 habitat types.
Similar to our study, Bayne and Hobson (1998) did not find a difference in smallmammal
abundance between edges and forest interior in Saskatchewan. In contrast,
Osbourne et al. (2005) found greater diversity and abundance of small mammals on
edges compared to interior-forest sites in West Virginia. Unlike our study, they found
additional, open-habitat species such as Microtus pennsylvanicus (Ord) (Meadow
Vole ) at edge sites, resulting in greater small-mammal diversity and abundance.
Although we found greater small-mammal abundance in larger patches, we did
not find an area effect for small-mammal richness. In a study of forest fragments
embedded in a matrix of agricultural land in west-central Indiana, Nupp and Swihart
(2000) found that species richness increased as a function of patch size and was
highest in continuous forest sites. Whereas the range of patches selected by Nupp
and Swihart was 0.1–150 ha, our sites were all embedded within patches averaging
96 ± 21 ha (range = 6–380 ha), perhaps too large to detect a species-area relationship
for small-mammal species.
Our results for individual species correspond well to those reported by previous
researchers. In a mixed boreal forest in Saskatchewan, Deer Mice were more abundant
in farm–woodlot–edge habitat compared to interior forest (Bayne and Hobson
1998). Similarly, Diffendorfer et al. (1995) recorded that Deer Mice reached highest
densities in landscapes with small patches of habitat in old fields in Kansas.
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Although this species was not significantly more abundant at developed-edge sites
in our study, we found their abundance tended to be greater in landscapes with more
developed edge within 500 m, primarily in the form of pasture habitat.
The White-footed Mouse is commonly considered a habitat generalist (Bellows
et al. 2001) that uses both edges (Nupp and Swihart 2000) and forest interior (Wolf
and Baltzi 2002, 2004). Nupp and Swihart (2000) found that White-footed Mouse
did not respond to patch size, and Anderson et al. (2003) found that patches with a
greater proportion of edge habitat and more complex understory vegetation (typically
smaller patches) had higher White-footed Mouse densities. Wolf and Batzli
(2004) did not find significant differences in food availability between interior
and edge sites and between prairie and agricultural edges to explain patterns of
White-footed Mouse habitat use in east-central Illinois. They suggested that forest
edges, particularly natural prairie edges, might be lower-quality habitat compared
to interior sites due to higher risks of predation. In our study, White-footed Mouse
abundance did not differ among habitat types, and abundance did not differ based
on vegetation measures, indicating that this species is also a habitat generalist in
northern Massachusetts.
Although White-footed Mouse abundance did not differ based on edge-type
category in our study, we found significant differences based on landscape patterns.
White-footed Mouse abundance increased with patch size, seemingly counter to
findings from other studies. For example, Yahner (1992) found that White-footed
Mouse was not negatively affected by the degree of fragmentation in managed
Pennsylvania landscapes and actually increased as fragmentation increased. Yahner
suggested that small area-requirements for White-footed Mouse reduced the
negative impact of fragmentation. In addition, Anderson et al. (2006) reported that
White-footed Mouse abundance did not differ based on patch size and amount of
forest-edge habitat. We also found that White-footed Mouse abundance was positively
related to wetland edge within 200 m, suggesting that although this species
may be a habitat generalist at smaller scales (edge category and vegetation level),
wetland edges may be an important landscape component for this species in New
England. That we found landscape-level responses suggests that the scale at which
White-footed Mouse habitat use should be measured requires further study.
Our results on White-footed Mouse and Deer Mouse should be regarded with
caution, even though the patterns we found for these two species in part corroborate
results from other studies. We separated these 2 species morphologically in the
field based on tail, foot, ear, and body measurements (Choate 1973, Lindquist et al.
2003); however, we did not collect saliva or tissue samples to positively identify
each individual through molecular analysis, and differentiating species in the field
has not been reliable (Lindquist et al. 2003, Rich et al. 1996). Given the similarity
in morphology and the regional overlap in habitat of these 2 species in New England
(Parren and Capen 1985), we also analyzed the combined Peromyscus species. This
combined variable for adults was not associated with any landscape metric, but was
associated positively with conifer basal area (Table 3). In contrast, abundance of
Peromyscus juveniles responded to both vegetation and landscape metrics.
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In our analysis of Red-backed Voles, we found that abundance was associated
with both vegetation and landscape metrics (e.g., positively related to patch size).
In contrast to our findings, Yahner (1992) found no difference in abundance of Redbacked
Voles in landscapes with differing levels of fragmentation. Yahner noted that
Red-backed Voles might prefer fragmented landscapes where the presence of specific
microhabitats preferred by this species might be more likely. Similarly, Bayne
and Hobson (1998) did not find an effect of patch size or a difference between edge
and interior habitats on abundance of Red-backed Vole. Furthermore, Fuller et al.
(2004) reported that while fragmentation through forest harvesting did not reduce
habitat quality for Red-backed Vole in central Maine, several vegetation measures
relating to a humid microclimate impacted Red-backed Vole abundance. In our
study, natural-edge sites associated with wetlands supported an average of 5 times
more Red-backed Vole individuals than drier habitats, and although not significant,
this pattern corresponds to the humid microclimate noted by Fuller et al (2004). We
also found that Red-backed Voles responded to vegetation differences. The positive
relationship that we found between abundance of Red-backed Voles with lower deciduous
density but greater conifer basal area may relate to the habitat preference for
moist microenvironments with a low density of overstory trees reported by Yahner
(1992) and composition of humid mixed forest by Fuller et al. (2004).
Our findings that Eastern Chipmunk abundance increased in smaller patches and
with lower overstory-tree richness are not surprising. This species is commonly
found in residential habitat (Ryan and Larson 1976, Schulze et al. 2005). In addition,
Mahan and Yahner (1998) reported that Eastern Chipmunk did not respond to
fragmentation differences in a managed forest in Pennsylvania. Furthermore, they
found physiological differences based on acorn-crop production, indicating a close
relationship to a limited number of overstory-tree species.
Our findings of landscape-level fragmentation associated with individual species
and community measures (e.g., positive relationship between Red-backed Vole
and patch size) that are missing in other studies may relate to the degree of connectivity
in our study. The landscape in our region had extensive forest cover (48%
within 500 m of sites) compared to other studies cited above, perhaps impacting
the relative influence of landscape fragmentation on different species. In contrast,
work by Yahner (1992) was conducted in a heavily managed forest in Pennsylvania;
Nupp and Swihart (2000) studied mammals in an agriculturally dominated landscape
in Indiana; and Wolf and Batzli (2002, 2004) focused on prairie landscapes
in Illinois. In other words, small-mammal populations were not isolated from one
another in our study area. Furthermore, several of these studies (Bayne and Hobson
1998, Nupp and Swihart 2000) were conducted in communities with a single Peromyscus
species, perhaps influencing habitat-use patterns. These differences provide
interesting contrasts for further study.
Although we found considerable differences in vegetation structure and landscape
characteristics among habitat categories in this study, together they did not
result in significant differences in community-level and population-level measures
for small mammals. Two years of field-work is a standard approach for smallNortheastern
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mammal studies, but this amount of trapping may not be enough to delineate actual
differences among habitats. Additional years of trapping might yield significant differences
if any variation exists among years. Alternatively, increasing the number
of study sites, although logistically challenging, may have helped to elucidate significant
patterns. Future work in this region should include more abrupt developed
edges, such as between forest and recent suburban development, compared to the
pasture or agricultural edges in this study. We recommend additional research to
build on the growing body of literature on multiscale habitat-use by small mammals
in eastern North America, particularly with reliable distinction between Peromyscus
species through molecular techniques.
Acknowledgments
We thank the Gordon College Department of Biology for providing the resources for the
completion of this project and the Massachusetts Trustees of Reservations for allowing us
access to their reserves. Funding for vegetation and GIS analyses was generously provided
by the Nuttall Ornithological Club through the Charles Blake Fund.We appreciate manuscript
review provided by K. Preedom and anonymous reviewers.
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