C. Maisonneuve, S. Rioux Agriculture, Ecosystems and Environment 83 2001 165–175 171
species represented less than 2 of captures and niche breadth values were not calculated.
4. Discussion
4.1. Small mammals Abundance and richness of small mammal species
clearly increased with increasing complexity of the vegetation structure in riparian strips. Similar results
were obtained in shelterbelts by Yahner 1983 and Dambach 1948, who contended that linear habitats
with all the vegetation strata shelter a greater abun- dance and diversity of small mammals. Vertical strat-
ification of the vegetation reduces predation risk by providing a better cover Stamp and Ohmart, 1978.
Although similar small mammal diversities were observed in herbaceous and wooded riparian strips, the
overlap index of small mammal communities in these habitat types was lowest, indicative of differences in
composition. These differences were ascribed to the high presence of some specialist species in wooded
strips P. maniculatus, Sorex fumeus or low abun- dance in herbaceous strips C. gapperi. Contradictory
results obtained from other studies on P. maniculatus were due to the existence of subspecies with extreme
habitat requirements. P. maniculatus bairdii is associ- ated with cultivated fields and prairies in the United
States Hooper, 1942; Hansen and Warnock, 1978; Fleharty and Navo, 1983, where it is considered as a
pest Linduska, 1949, whereas P. maniculatus gracilis and P. maniculatus abietorum mostly occupy forested
habitats in the Maritimes and up to the St. Lawrence River Hooper, 1942; Iverson et al., 1967; Banfield,
1974. S. fumeus is considered more habitat selective than S. cinereus and is more abundant in humid de-
ciduous or mixed forests with soils covered with deep humus Hamilton, 1940; Wrigley, 1969, in agreement
with the present results. C. gapperi is generally con- sidered a specialist species characteristic of wooded
habitats Iverson et al., 1967; Miller and Getz, 1977; Yahner, 1983; it has a relatively high water turn-over
rate and poorly efficient kidneys, impeding its survival in low humidity Getz, 1968. It has been shown that
Peromyscus leucopus, another forest dwelling species Getz, 1961b; Kaufman and Fleharty, 1974; Snyder
and Best, 1988, can use riparian herbaceous strips as corridors between woodlots Cummings and Vessey,
1994. Generally considered a typical species of prairies
and other open grass-dominated habitats Iverson et al., 1967; Grant, 1971; Morse, 1973; Yahner, 1983;
Manson et al., 1999, M. pennsylvanicus was more abundant in herbaceous riparian strips, but many in-
dividuals were also caught in shrubby and wooded strips, leading to the fourth highest niche breadth
value obtained. Some studies found M. pennsylvan- icus in forested habitats Dowler et al., 1985, and
others attributed its presence to irregular incursions in times of high population densities and suggested
that it avoids forest habitats Grant, 1971; Tamarin et al., 1984. In shelterbelts, the species is present
in openings and avoids the more wooded sections Yahner, 1982. The shrubby and wooded riparian
strips studied here were generally regularly broken by small openings, which probably was the reason
for the presence of M. pennsylvanicus.
Linduska 1949 suggested that M. musculus, con- sidered a pest species, rarely inhabits linear herba-
ceous habitats during the summer, but occupies these habitats after adjacent fields have been harvested. A
good part of the present sampling was carried out after harvest, and only 14 individuals were captured, half
of these in herbaceous strips, indicating a probable selection for this habitat type. M. musculus sometimes
prefers linear marginal habitats to cultivated prairies, hayfields and corn fields Clark et al., 1996; Kirsch,
1997. The low abundance of this species in this study could reflect its distribution in the agricultural
landscape, in agreement with Kaufman and Kaufman 1990 who suggested that M. musculus is rarely, if
ever, abundant in prairies and in cultivated fields. Linear habitats such as riparian strips could simply
be corridors between farm buildings Merriam, 1988; Clark et al., 1996.
Z. hudsonius, S. cinereus, and B. brevicauda were the most abundant species and were present on all the
study sites. The greatest niche breadth values were also obtained for these three species. Many other stud-
ies confirmed that these species are generalists in their habitat selection Quimby, 1951; Iverson et al., 1967;
Getz, 1961a,b; Rickard, 1960; Brown, 1967; Dueser and Shugart, 1978; Wrigley et al., 1979; Yahner, 1982;
Adler, 1985; Dowler et al., 1985; Snyder and Best, 1988. Humidity seems to have a greater influence than
172 C. Maisonneuve, S. Rioux Agriculture, Ecosystems and Environment 83 2001 165–175
vegetation on habitat selection by Z. hudsonius and B. brevicauda Quimby, 1951; Getz, 1961a; Choate and
Fleharty, 1973, and the proximity of streams could explain their preponderance in this study. In spite of
its generalist nature, B. brevicauda was less abun- dant than expected in riparian strips adjacent to cereal
fields. Although this species may avoid corn fields, this avoidance does not reduce its use of linear habi-
tats adjacent to corn fields Kirsch, 1997. Low avail- ability of prey species within buffer strips adjacent
to cereal fields could probably have influenced our results.
4.2. Herpetofauna As for small mammals, the abundance of the her-
petofauna increased with increasing complexity in vegetation structure, and the diversity of herpetofaunal
communities of herbaceous and wooded strips were similar. However, contrarily to what was obtained for
small mammals, richness and diversity were greater in shrubby riparian strips. The lowest overlap index
obtained between riparian strip-types was between shrubby and wooded riparian strips. This difference
was mostly due to the presence of species in shrubby strips which were absent from wooded strips Am-
bystoma maculatum, Hyla crucifer, Storeria occipit- omaculata and to a greater abundance of R. pipiens
in wooded strips.
Only three out of 11 species were caught on more than 20 occasions. This low sample size reduced the
possibility of any conclusion in terms of habitat se- lection. B. americanus clearly was most generalist,
having the highest niche breadth value and being detected in all sites but two located in herbaceous
riparian strips, in agreement with previous studies Leclair, 1985; Dubé, 1994; deMaynadier and Hunter,
1998.
R. pipiens is generally considered a species of open habitats, fields and prairies Dole, 1965; Cook, 1984,
vegetation structure being the main factor for habi- tat selection with a preference for good gramineous
cover Beauregard and Leclair, 1988, no shrubs and reduced litter Dubé, 1994. The majority 88 of the
individuals were caught in wooded riparian strips, giv- ing this species a relatively low niche breadth value.
The wooded riparian strips in this study often had a rich herbaceous cover without any shrub layer, which
would provide adequate habitat for R. pipiens. It is, however, more difficult to interpret the absence of this
species in herbaceous riparian strips. More than 75 of R. sylvatica were captured in
shrubby riparian strips, leading to a relatively low niche breadth value. This species is generally asso-
ciated with wooded habitats Heatwole, 1961; Bellis, 1962 and is considered intolerant to habitat modi-
fications deMaynadier and Hunter, 1998. Air and substrate moisture are important factors in the pro-
cess of habitat selection Marshall and Buell, 1955; Roberts and Lewin, 1979, the dense vegetation in
the shrubby riparian strips studied probably explained the preponderance of R. sylvatica there.
5. Conclusions
