Reducing Populations of an Invasive Ant Influences Survival, Growth, and Diet of Southern Toads (Anaxyrus terrestris)

The southeastern United States supports some of the greatest levels of amphibian diversity in North America, and several species are in decline. Invasive species in the southeastern United States, such as the red imported fire ant (Solenopsis invicta; hereafter RIFA), may be a factor in amphibian declines via depredation, injury of, and/or competition with native amphibians for arthropod prey. Our objective was to assess the influence of RIFAs and RIM reductions on the diet, growth, and survival of Southern Toads (Anaxyrus terrestris). In 2013 and 2014 we randomly assigned juvenile toads into enclosures either treated with an insecticide, hydramethylnon, to reduce RIFAs (hereafter RIFA treatment) or maintained with ambient levels of RIFAs (hereafter control; n = 4 enclosures per treatment). The mean proportion of recaptured toads was 9.5 and 21 times greater in the RIFA treatment compared to the control in 2013 and 2014, respectively. Toads in the control enclosures were 23% larger at the end of the study than toads recaptured in the RIFA treatment enclosures, though this was driven largely by differences in toad densities. Toad diets in the control and RIFA treatment enclosures overlapped 94%. When considering the dietary overlap of different ant genera only, the dietary overlap was 44%. Our study provides evidence RIFAs alter amphibian populations and may be contributing to amphibian declines in the southeastern United States. Given the high mortality rates we observed, RIFAs should be considered when developing conservation plans for any amphibian species found in areas where RIFAs are present.