Examining native invasive species: Effects on amphibian communities experiencing multiple stressors.
Boone, Michelle1, 1 Miami University, Oxford, OH, USA
ABSTRACT- Bullfrogs (Rana catesbeiana) are often found in newly created permanent wetlands, are an exotic species that has spread in the western US and Europe, are implicated in amphibian declines in the US, and are listed as one of the 100 worst invasive alien species by the IUCN. For these reasons, bullfrogs may be considered an invasive species that could affect populations both within and outside its native range. In my studies, I have examined the effects of overwintered tadpoles on aquatic amphibian communities experiencing differential stress, including contaminants (nitrate fertilizer and the insecticide carbaryl) and a pathogenic fungus (Saprolegnia ferax). Amphibian communities containing both anuran and caudate species were created in experimental mesocosms and amphibians were reared from hatching through metamorphosis. Generally, overwintered bullfrogs did better in conditions with one or more stressors, while anurans and caudates did not. This result suggests that the positive response of bullfrogs to stress may favor their ability to survive in compromised environments and allow them to increase their density on the landscape. Overwintered bullfrog tadpoles had negative effects by reducing survival and mass at metamorphosis of amphibians through reduction in their algal food resources and trophic cascades. Exposure to sublethal contaminants and a pathogenic fungus alone often had positive effects on amphibians, largely through effects on plankton resources. However, when these stressors occurred in the presence of overwintered bullfrog tadpoles, amphibians were negatively affected. These results suggest that amphibians within the native range of bullfrogs are negatively impacted by them and that the presence of additional stressors can magnify the effect. This research highlights the role multiple stressors may play in influencing amphibian populations and suggests that bullfrogs can have negative impacts on communities within their native range.
Key words: invasive species, multiple stressor, contaminants, pathogen
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