Summary1. There is significant concern over the impacts of plant invasions on habitat quality for native fauna. Recent research suggests that non-native Purple Loosestrife ( Lythrum salicaria ) invasions may negatively affect the performance of larval American Toad tadpoles ( Bufo americanus ), and that compounds leached from L . salicaria leaves play a direct or indirect role in this effect. 2. We raised individual B. americanus and Gray Treefrog ( Hyla versicolor ) tadpoles on high-quality diets in aqueous extracts of senescent leaves from L. salicaria , native Broad-Leaf Cattail ( Typha latifolia ), and control water to determine whether loosestrife extracts directly affect anuran tadpole performance. 3. Even at high artificial food levels, B. americanus survival was significantly lower in L. salicaria extracts compared with T. latifolia extracts and a water control. Food level strongly affected B. americanus development, but tadpoles raised in L . salicaria extract were less developed compared with conspecifics raised in cattail extract or water. Unlike B. americanus, Hyla performance was not affected by exposure to any plant extract compared with the water control. 4. Our study implicates secondary plant compounds as a mechanism underlying the impact of an invasive plant on some but not all native fauna. We hypothesize that high tannin concentrations of L . salicaria leaves have the potential to create environments that are directly toxic to B. americanus tadpoles. We hypothesize that obligate gill breathers such as B. americanus tadpoles are highly sensitive to gill damage caused by high concentrations of phenolics. Other anuran species such as H. versicolor that develop well-functioning lungs early may be less affected by high tannin concentrations.

Introductions of non-native predators and competitors appear to contribute to worldwide amphibian declines; however, potential negative impacts of invasive plants on habitat quality and amphibian populations have not been examined. Loss of diversity and alterations in ecosystem function associated with plant invasions may disrupt food webs, potentially leading to further declines of already threatened amphibian populations. We used a combination of small bins, mesocosms, and field experiments to examine the impacts of Eurasian purple loosestrife (Lythrum salicaria) replacing native cattails (Typha latifolia) in North American freshwater wetlands on survival, developmental rate, and diet (freshwater algae) of American toad (Bufo americanus) tadpoles. Tadpoles developed slower in L. salicaria compared to tadpoles developing in T. latifolia. This effect was consistent across experimental venues, although mesocosms showed this effect only in the second year of our study. Survival and development rates were always more variable in purple loosestrife than in cattail. In bins, tadpoles showed significantly reduced survival when raised in purple loosestrife extract and addition of leaf litter exacerbated this negative effect. Tadpole survival rates in mesocosms and field cages were not significantly different between plant species, most likely an effect of high variability among replicates. We suspect a combination of direct toxicity of high tannin concentrations in L. salicaria leaves and their indirect negative impacts on aquatic food webs are responsible for these results. Tadpole gut analyses revealed differences in algal communities among venues and between L. salicaria and T. latifolia suggesting that alterations in tadpole food quality and quantity contribute to the observed reduced tadpole performance. The replacement of native wetland plant species by L. salicaria does not represent a simple exchange of ecological equivalents and the function of invaded habitats for native species has clearly changed. While we were investigating only a single amphibian species, our results suggest that the impact of L. salicaria on ecosystem processes and aquatic food webs may be more general and likely to negatively affect other wetland species. The threats non-indigenous plants represent for amphibian populations and food webs may be underestimated, and warrant further investigation.

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