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Forces structuring tree squirrel communities in landscapes fragmented by agriculture: species differences in perceptions of forest connectivity and carrying capacity


  • Jacob R. Goheen,

  • Robert K. Swihart,

  • Thomas M. Gehring,

  • Michael S. Miller

J. R. Goheen, R. K. Swihart, T. M. Gehring and M. S. Miller, Dept of Forestry and Natural Resources, Purdue Univ., West Lafayette, IN 47907-1159, USA. Present address for JRG: Dept of Biology, Univ. of New Mexico, Albuquerque, NM 87131, USA. Present address for TMG: Dept of Biology, Central Michigan Univ., Mount Pleasant, MI 48859, USA.


The North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into the central hardwoods of the United States in conjunction with increasing forest fragmentation and declining gray squirrel (Sciurus carolinensis) populations. We used translocation experiments and patch occupancy data to test for interspecific differences in mobility and sensitivity to habitat loss and modification by agriculture. We released squirrels in fencerows to test the hypothesis that gray squirrels display inferior mobility relative to red and fox (S. niger) squirrels. Elapsed time to movement from fencerows for 76 individuals increased with distance to forest patches and harvesting of crops. Gray and red squirrels took longer to move from fencerows than fox squirrels, and gray squirrels were less successful at moving from fencerows than red and fox squirrels. Ecologically scaled landscape indices revealed the degree to which interspecific differences in mobility and individual area requirements accounted for the occurrence of these species across landscapes. Gray squirrel distribution was constrained both by individual area requirements and dispersal ability. Occurrence of red and fox squirrels was related to patch size but was unaffected by landscape connectivity.