Anthropogenic acid deposition has led to aquatic and terrestrial ecosystem degradation, and the resulting acidification can affect individuals, populations, and communities. Differences in the pH of a system could have positive or negative effects on communities through direct physiological effects or indirect trophic effects on predators and prey. We studied the effects of soil pH on American toads and the leaf litter invertebrate community in forests of northeast Ohio. These forests have been part of an eight-year study on pH elevation, providing the opportunity to test for the effects of acidification on communities by comparing locations with acidified soils and locations with elevated pH. We tested if long-term pH elevation affected post-metamorphic toad growth and survival as well as invertebrate abundance. We placed American toad metamorphs in 1 m2 enclosures in nine forest plots with elevated soil pH and nine control forest plots. We measured growth after 25, 60, and 90 days as well as survival to day 90. Toad stomach contents were collected after 90 days to test for an effect of soil pH on toad diet. We also conducted pitfall sampling to compare invertebrate abundances between pH elevated forest plots and control forest plots.
Results/Conclusions
Toad survival did not differ between forest plots with elevated soil pH and control plots. However, toads in forest plots with elevated pH tended to be larger (1.04 g ± 0.12 s.e.) after 90 days compared to toads in control plots (0.89 g ± 0.11 s.e.). There were no differences in diet of toads surviving to day 90 between elevated pH plots and control plots. We also found no differences in abundances of the most common invertebrate groups collected from pitfalls between plots with elevated pH and control plots. We observed a positive correlation between toad mass and Collembola abundances at the end of the study regardless of soil pH, indicating that invertebrate abundances influence growth of forest floor amphibians in habitats with either acidic or elevated soil pH. Our results provide evidence that ecosystem acidification may negatively affect American toads, although not due to changes in prey availability. Changes in invertebrate communities, however, may be better attributed to other anthropogenic factors such as land use change and pesticide use.