Interaction between invasive plant leaf litter and NaCl on two model amphibians.
Human activities are rapidly changing natural environments, often with harmful consequences for native communities. The introduction of invasive species is particularly damaging to native communities, especially when invasive species alter the chemical environment and create novel, stressful conditions. These abiotic conditions are predicted to favor other stress-tolerant organisms, potentially shifting community abundance and diversity over time. However, few environments are free of other anthropogenic stressors (i.e., chemical contaminants), which can also influence patterns of abundance and diversity. Therefore, to understand the impacts of invasive species, we need to consider their potential interactions with other anthropogenic stressors. Towards this goal, we tested how leachates from invasive plants and road salt impacted a model amphibian that is native to the U.S. (northern leopard frog, Lithobates pipiens) and a model amphibian that is non-native to the U.S. and considered invasive in some localities (African clawed frog, Xenopus laevis). We examined the effects of native and invasive leaf litter leachate and sublethal NaCl concentrations on amphibian development, size, and tolerance to a lethal concentration of NaCl. Exposure to invasive leaf litter and sublethal NaCl both accelerated hatching time in leopard frogs, but neither affected hatching time in Xenopus. Exposure to invasive leaf litter also led to reduced mass and tolerance to lethal NaCl concentrations in the leopard frog, but had no effect on mass and led to increased tolerance to lethal NaCl concentrations in Xenopus. These findings suggest that invasive leaf litter leachate impacts these amphibian species differently, being more stressful to the leopard frog than Xenopus. Further, we demonstrate that the presence of a pollutant may augment the effect of invasive leaf litter on amphibians, highlighting the need to consider concurrent stressors in invasive species management.