An Experimental Examination of an Artificial Dispersal Sink

Abstract

Studies of artificial dispersal sinks (removal experiments) assume that they measure the dispersal pattern that would occur in an unmanipulated population. i conducted a removal experiment on the California ground squirrel, Spermophilus beecheyi, to test this assumption. The sex ratio of young immigrants removed from the artificial dispersal sink (0.72 males/female) was lower than that of young immigrants to an adjacent reference area (1.64 males/female), young immigrants to reference areas 1 km away (4.13 males/female), and young emigrants in an earlier study of the species (2.55 males/female). Similar results occurred in a study of the Arctic ground squirrel, S. parryii, conducted by J. E. Green. I conclude that removal data cannot be assumed to represent an accurate measure of the dispersal, or the characteristics of dispersers, occurring in unmanipulated populations of ground squirrels.