Determining population boundaries and densities of red-eared slider turtles (Trachemys scripta) : an empirical field test.

Abstract

Source-sink metapopulations consist of large source subpopulations surrounded by smaller sink subpopulations where predictable migrations correlate with habitat favorability. From 1996-2003, Trachemys scripta were trapped in a permanent pond in central Oklahoma. In 2003, drought resulted in an influx of unmarked adults, presumably immigrants from nearby ephemeral ponds, suggesting a source-sink metapopulation. From 2004-2006, I sampled 14 ponds, and analyzed migration data from 1996-2003 to select among population models. My objectives were to define natural population boundaries, test the source-sink hypothesis, and estimate migration rates and population density. From 1996-2006, 18,285 captures of 2,087 turtles were recorded, including 622 migrants. The direction of migrations supported the source-sink hypothesis. Migrations were negatively correlated with inter-pond distance. Using POPAN, population density estimates from 2005 were 135 individuals/ha, compared to 364 individuals/ha from 2003. These results suggest that long-term population studies should expand sampling to include multiple ponds in order to account for migration.