. The Canadian field-naturalist. 246 The Canadian Field-Naturalist Vol. 98. Figure I. Study area. 1 — Hogg Is., 2 — Thrum Cap; 3 — Blackberry Is.; 4 — Sherosels.; 5 — One Tree Is.; 6 — Bald Thrum; 7 — Cove Thrum; 8 — Banks Is.; 9 — Pound Is. leucopus are both woodland species, and generally require larger islands (Crowell 1973). The islands containing only C. gapperi were predomi- nantly wooded, but contained some habitat suitable for Microtus. The apparent absence of the latter from these two islands may only reflect the extremely low numbers of M. pennsylvanicus on the adjacent mainland at t
. The Canadian field-naturalist. 246 The Canadian Field-Naturalist Vol. 98. Figure I. Study area. 1 — Hogg Is., 2 — Thrum Cap; 3 — Blackberry Is.; 4 — Sherosels.; 5 — One Tree Is.; 6 — Bald Thrum; 7 — Cove Thrum; 8 — Banks Is.; 9 — Pound Is. leucopus are both woodland species, and generally require larger islands (Crowell 1973). The islands containing only C. gapperi were predomi- nantly wooded, but contained some habitat suitable for Microtus. The apparent absence of the latter from these two islands may only reflect the extremely low numbers of M. pennsylvanicus on the adjacent mainland at the time. On the island containing C. gapperi and M. pennsyl- vanicus only, competitive exclusion, suggested for these two species by Grant (1970b), had obviously not occurred. We are unaware of any previous reports of this species pair alone on a coastal island. Its presence may simply bedue to chance (Simberloff and Connor 1981). Alternatively, coexistence may be facilitated by unfavorable climate, or by predation, both of which might dampen competition by preventing the buildup of high densities (Wiens 1977). In southwestern Nova Scotia winters are particularly harsh for small mam- mals because of extreme temperature fluctuations and lack of a persistent protective snow cover (Gates 1975). On the two islands inhabited by all three rodent species, densities of all species were relatively low on one (Banks), but on the other (Hogg) densities of C gapperi and M. pennsylvanicus, in particular, were relatively high. Not only did these three species coexist on Hogg Island, but there was little evidence of habi- tat segregation. Often multiple captures (nine double, one quadruple) at single trap points, C. gapperi and M. pennsylvanicus were captured together at three. In addition, the two species were caught at adjacent trap points more frequently than any other species combi- nation (Thurber 1982). Oddly, more C. gapperi than M. pennsylvanicus were caught near the
Size: 1581px × 1581px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorottawafieldnaturalistsclub, bookcentury1900, bookcolle
