Great Basin Naturalist


Four populations of the spotted frog, Rana pretiosa, occur in western Bonneville Basin. Only the Tule Valley populations occupy aquatic habitats associated with warm (28 °C) and slightly saline (1700–2700 µmhos/cm) springs. The spotted frog in Tule Valley breeds in cold-water portions of the peripheral wetlands, which exhibit maximum temperature variations (1–25 °C), maximum conductivity up to 3200 µmhos/cm, and maximum pH values up to 9.7. Adult frogs are found in habitats with temperatures of 29 °C, conductivity of 4700 µmhos/cm, and pH above 9.0 in the summer. The increased summer salinity and pH in frog habitats returns to lower values by the next breeding season due to underground recharge. Breeding in Tule Valley occurs earlier than in other Bonneville locations because of the warm-water sources. Spatial and temporal distribution of the spotted frog since the regression of Lake Bonneville 15,000 years ago and threats to present habitats are discussed.