Is bigger always better? Tadpoles grow larger and faster, but with lower survival when raised with an invasive plant

Background/Question/Methods

Invasion by non-native plants poses a significant threat to native wildlife. Quantification of the effects of plant invasion on wildlife has shown strong negative, neutral and even positive influences on biota from particular regions. However, an examination of the impact of plant invasion across several regions is lacking. To address whether plant invasion impacts amphibians and what mechanisms may be contributing to potential impacts, we used aquatic mesocosms to raise wood frogs (Lithobates sylvaticus) from two regions of the United States with leaf litter from invasive purple loosestrife (Lythrum salicaria), native hardwood trees, and a mixture of both. We examined several metrics of amphibian fitness, including survival, number of days to metamorphosis, and size at metamorphosis. Further, we quantified whether the effects of purple loosestrife could translate to variation in anuran biomass or standing stock of nitrogen or phosphorus export. 

Results/Conclusions

Our results show purple loosestrife negatively influenced survival of wood frogs, but decreased time to metamorphosis and increased size of metamorphic individuals in two different regions of the United States. Postmetamorphic anuran size was predicted by quality of purple loosestrife plant material compared to native hardwood plant material. Despite the decrease in survival, the increase in size of post-metamorphic anurans raised with purple loosestrife resulted in anuran biomass and standing stock of N and P export to be similar across treatments at both locations. These results suggest purple loosestrife could have significant consequences to the survival of anuran larvae; however, these differences do not translate to significant variation in biomass or nutrient export of anurans.