Diets of Syntopic Black-knobbed Sawbacks (Graptemys nigrinoda) and Alabama Map Turtles (Graptemys pulchra) in the Alabama River

Abstract

Abstract The emydid turtle genus Graptemys is characterized by intra- and interspecific dietary diversity. Sympatric species pairs typically differ in trophic morphology and dependence on bivalve mollusks in female diets, yet there is a lack of comprehensive comparisons of the diets of sympatric species. I collected feces from 92 black-knobbed sawbacks (G. nigrinoda) and 54 Alabama map turtles (G. pulchra) from the Alabama River at a site in Autauga and Lowndes counties, Alabama. Samples were analyzed separately for unsexed juveniles, adult males, juvenile females larger than the smallest mature males, and adult females of each species. Sponges, aquatic insects (particularly caddisfly larvae), and filamentous algae were the primary foods of G. nigrinoda. Native mussels, invasive Asian clams, and aquatic insects (but few caddisfly larvae) were the primary foods of G. pulchra. Each of the four sex and size classes exhibited substantially greater similarity with conspecific classes than with classes of the o...