164 Mary K. Clark, Michael S. Mitchell, and Kent S. Karriker 
Phillips, Refuge Manager, personal communication). Trapping fre- 
quency has been high and efforts have covered all wetland and 
upland habitats, so it is unlikely that S. cooperi occurs on the 
Albemarle-Pamlico peninsula. 
Doutt et al. (1973) suggested that the major feature common 
to all Synaptomys habitats was that they were marginal for Microtus, 
and Linzey (1983) documented competitive exclusion of Synaptomys 
by Microtus in Virginia. Results from the National Forest investiga- 
tion and Clark et al. (1985) seem to lend further support to this 
relationship. No Microtus pinetorum were caught in the National 
Forest stands in which Synaptomys were captured, but 13 M. 
pinetorum were caught in one of the other short pocosin stands. 
Additionally, M. pennsylvanicus was abundant in wet, early succes- 
sional communities on the Dare County mainland (Clark et al. 1985). 
The geographic distribution and genetic structure of modern 
populations are determined by historical patterns of dispersal as well 
as current ecological associations. The presence of S. cooperi south 
of the Dismal Swamp is not unexpected when one considers that 
the late Pleistocene range of S. cooperi extended much farther south- 
ward than the present range. Pleistocene fossil records are known 
from as far south as Citrus County, Florida (Linzey 1983). In Wetzel’s 
(1955) examination of the subspeciation and dispersal of the south- 
ern bog lemming, he determined that S. c. helaletes does not differ 
so greatly from the nearest form ( S . c. stonei) as did the other 
subspecies he studied. The close relationship was attributed to a 
relatively recent loss of interconnecting range. 
Pocosin habitats might have provided refugia for species at 
the extreme limits of their distributions since the Pleistocene. Ther- 
mal properties of evergreen vegetation and saturated soils character- 
istic of pocosins likely provide a buffer from temperature extremes. 
Clark et al. (1985) reviewed the role of late Pleistocene climates as 
they relate to some small mammal distributions in the south- 
eastern United States and noted that in pocosin areas both northern 
and southern faunal elements co-exist in local refugia supported by 
subclimax communities. 
Zoogeographically, a number of Atlantic Coastal Plain 
mammals presently reach either northern, southern, or eastern limits 
of distribution in pocosin-rich areas. Other taxa formerly believed 
to be confined largely to the Dismal Swamp, such as Blarina 
brevicauda telmalestes and Microtus pennslyvanicus nigrans , have 
been documented south of the Dismal Swamp area (Lee et al. 1982, 
Clark et al. 1985). The star-nosed mole ( Condylura cristata parva) 
also has a broader distribution on the southeastern Coastal Plain 
