Comparison of dietary overlap between allopatric and sympatric geckos
Two gecko species, Hemidactylus turcicus and Cyrtopodion scabrum, have been introduced into the Port of Galveston, Texas. While H. turcicus has been established for a longer period of time, the relatively recent introduction of C. scabrum near the entrance of the Port has apparently led to the displacement of H. turcicus in that area. This has resulted in a distribution in which the two populations’ are largely allopatric except for a narrow band of sympatry at the periphery of each of their ranges. We examined stomach contents of both species in allopatry and sympatry in order to determine if dietary overlap in sympatry is less than that in allopatry. We calculated Pianka's (1973) symmetric overlap for geckos occupying sympatric areas (0.55) and allopatric areas (0.81). We found significant differences between the resource utilization distributions of the two species in sympatry but not in allopatry. In addition, we compared overlap between allopatric and sympatric populations within each species and found that the differences in resource utilization between the two species in sympatry was due to a dietary shift exhibited in H. turcicus but not C. scabrum. Observed differences in resource utilization may be a response to competition between these two species in sympatry which may have led to the exclusion of H. turcicus on areas of the docks occupied by this species prior to the introduction of C. scabrum.