Geographic Variation in Fox Squirrels (Sciurus niger) and Gray Squirrels (S. carolinensis) of the Lower Mississippi River Valley

Abstract

Geographic variation was studied in fox squirrels ( Sciurus niger ) and gray squirrels (5. carolinensis ) by comparing patterns of differentiation within and between these two sympatric species in the lower Mississippi River valley. Geographic patterns of variation were apparent in the morphology and allozymes of both species. Patterns of differentiation in morphologic and allozymic characters are similar between species; however, morphologic variation is not congruent with allozymic variation within either species. Fox squirrels and gray squirrels vary morphologically in that, within each species, individuals inhabiting the Mississippi River floodplain and delta region are smaller than animals from adjacent areas. Allozyme analyses revealed that within each species, there are differences among eastern and western populations, as defined by their geographic location relative to the present channel of the Mississippi River. This study provides considerable evidence that the lower Mississippi River has influenced morphologic differentiation in fox squirrels and gray squirrels and that the river has impeded (and may still impede) gene flow in these species.