Food Web Linkages Demonstrate Importance of Terrestrial Prey for the Threatened California Red-Legged Frog

Abstract

Restoration efforts are ongoing to protect the threatened California Red-Legged Frog (Rana draytonii) from further decline, but conserving species that have aquatic and terrestrial life stages can be challenging. For example, although it is clear that aquatic habitat must be protected for breeding, less is known about the importance of terrestrial habitat. Food web linkages remain largely unknown for this species yet would offer insight on the source of prey items and, thus, the importance of each type of habitat. We used three methods to analyze food web linkages for the California Red-Legged Frog: 1) stable isotopes collected from frogs and key species in their ecosystem; 2) stomach contents sampled from live frogs in the wild; and 3) stomach contents sampled from museum specimens. The stable isotope mixing model found 99.7% of R. draytonii diet came from terrestrial prey. Wet and dry season stomach content samples flushed from captured frogs had 90% terrestrial prey, and museum specimens contained 82% terrestrial prey. These data suggest that conservation efforts should protect riparian and upland habitats adjacent to aquatic habitats in addition to aquatic habitats.