Invasion of New Aquatic Habitats by Male Freshwater Turtles

Abstract

Long-term field research often reveals how organisms respond to stochastic environmental events such as droughts (Gibbons et al., 1983) or changes in population structure or species composition over time (Tinkle, 1979; Parker, 1984; Pechmann et al., 1991). Studies on aquatic turtle populations have been conducted for more than 25 years on the US Department of Energy's Savannah River Site (SRS) near Aiken in the Upper Coastal Plain of west central South Carolina (Gibbons et al., 1982; Gibbons, 1990a; Frazer et al., 1991). One conclusion from these studies is that adult males residing in small, isolated wetlands are more likely than females to move overland and to move greater distances (Morreale et al., 1984). Factors reported to stimulate overland movements by freshwater turtles include travel to and from hibernacula (Bennett, 1972; Gibbons, 1986), pond drying/filling (Cagle, 1944; Sexton, 1959; Gibbons et al., 1983), nesting activity of females (Ernst et al., 1994), and mate-searching by males (Parker, 1984; Gibbons, 1986). Although male and female conspecifics probably exhibit similar terrestrial activity in some situations, differences in reproductive strategies should produce distinct terrestrial activity patterns. Previous studies have suggested that females sometimes travel long distances on land to nest but that males may also travel long distances overland seeking aquatic habitats containing females to inseminate (Morreale et al., 1984; Gibbons, 1986; Brown and Brooks, 1993). If these predictions are correct, males should be more likely than females to encounter new aquatic habitats, including those without conspecific populations. Therefore, colonizing or invading nonresident species should have malebiased sex ratios relative to established resident