Terrestrial Performance of Juvenile Frogs in Two Habitat Types after Chronic Larval Exposure to a Contaminant

Abstract

Chemical contamination and physical alteration of the environment can separately or in combination cause changes in the abundance and diversity of amphibian species. However, these factors are typically considered in isolation using experiments focused on single life stages. We examined the terrestrial performance (i.e., growth, survival) of Southern Leopard Frog (Rana sphenocephala) juveniles that had been chronically exposed to one of three initial concentrations of the heavy metal cadmium (0, 5, or 18 µg Cd/L) as aquatic larvae. Juveniles were reared in terrestrial enclosures within deciduous forest and open field habitats through their first growth season (summer to autumn). The effect of cadmium (Cd) on terrestrial survival depended on habitat type; survival increased with Cd concentration in the field enclosures and decreased with Cd concentration in the forest enclosures. Terrestrial survival was 73% in the forest enclosures and 54% in the field enclosures, but the difference was not significant. The trend for mass at metamorphosis to increase with Cd concentration was maintained through the first growth season, and frogs collected in autumn from the field enclosures were heavier than their counterparts in the forest. Individuals that survive larval Cd exposure may benefit from a large size, but carryover effects that reduce juvenile survival may occur in forest habitats. The conversion of forest habitat into open fields may be of mixed consequence to the Southern Leopard Frog, in the form of lower survival but better growth among the survivors.