Pesticides and Amphibians: The Importance of Community Context

Abstract

The widespread application of pesticides has attracted the attention of ecologists as we struggle to understand the impacts of these chemicals on natural communities. While we have a large number of laboratory-based, single-species studies of pesticides, such studies can only examine direct effects. However, in natural communities, species can experience both direct and indirect effects. We conducted an outdoor mesocosm experiment on aquatic communities containing three tadpole species (Hyla versicolor, Bufo americanus, and Rana pipiens), zooplankton, and algae. We then manipulated a factorial combination of predators (no predators; newts, Notophthalmus viridescens; and larval beetles, Dytiscus sp.) and pesticides (no pesticides, the insecticide malathion, and the herbicide Roundup). We found that Roundup (1.3 mg of active ingredient/L) had substantial direct negative effects on the tadpoles, reducing total tadpole survival and biomass by 40%. However, Roundup had no indirect effects on the amphibian community via predator survival or algal abundance. Malathion (0.3 mg/L) had few direct effects on the tadpoles. Malathion caused no indirect effects with one of the predators (red-spotted newts) but caused substantial positive effects on amphibians (a five-fold increase in total tadpole survival and biomass) due to the sensitivity of the predatory beetles to the insecticide. Thus, while high concentrations of malathion can directly kill larval anurans, more ecologically relevant concentrations can have large positive effects in mesocosms by removing predatory insects. These results make it clear that pesticides can have both direct and indirect effects in natural communities and that these effects critically depend upon the composition of the community.

Effects of the herbicide imazapyr on juvenile Oregon spotted frogs

“…The effects of predation, reduced water levels as ponds and wetlands dry during the summer, and/or high population densities can increase individual stress levels and potentially reduce fitness and survival. The presence of predators alone can increase nonconsumptive mortality in some tadpole species, presumably due to increased stress [19,20]. The toxicity of pesticides may also be altered in the presence of predators.…”

“…The toxicity of pesticides may also be altered in the presence of predators. Tadpoles in experimental mesocosm communities with a newt (Notophthalmus viridescens) predator experienced higher mortality when a glyphosate product with a toxic surfactant (Roundup with polyethoxylated tallow amine) was added [19,20].…”

Amphibians as indicators of changes in aquatic and terrestrial ecosystems following GM crop cultivation: a monitoring guideline

“…Pesticides are well known to affect amphibians (Bridges 1997;Brunelli et al 2010;Davidson 2004, Howe et al 2004Paganelli et al 2010;Relyea 2005a;Relyea 2005b;Relyea et al 2005). Though effects on individuals do not necessarily impair population viability (Forbes and Calow 2002;Rohr et al 2006;Schmidt 2004), an ultimate deterioration cannot be excluded.…”

Ecotoxicidade comparativa dos herbicidas da cana-de-acúcar para larvas de anfíbios

“…Esta variável foi escolhida pelo papel fundamental que taxa de atividade exerce em diversas atividades relacionadas à aptidão darwiniana, como na mediação do tradeoff entre evitar predadores e obter alimento (ANHOLT et al, 1996;RELYEA & WERNER, 1999;RELYEA, 2005 (HOWE et al, 1998).…”

“…Da mesma forma que através dos experimentos deste trabalho podemos evidenciar esta diferença na sensibilidade entre espécies, é muito provável que esta característica seja observada em muitas outras espécies e que este fato pode levar a mudanças na estrutura de comunidades, uma vez que algumas espécies são eliminadas por um pesticida específico e outras mais tolerantes se tornam dominantes (Relyea, 2005).…”