Effects of exotic common reed (Phragmites australis) on wood frog (Lithobates sylvaticus) tadpole development and food availability

Abstract

Exotic species contribute to aquatic habitat degradation. In the context of declining amphibian populations, the introduction of alien species has been the subject of numerous studies but few have been dedicated to exotic plants. We hypothesized that the establishment of the exotic common reed (Phragmites australis) in North America would lengthen larval anuran development and decrease the survival rate by modifying habitat structure, changing water characteristics, and decreasing food availability. We tested these hypotheses by studying the larval development of the wood frog (Lithobates sylvaticus) during an experiment in field enclosures. Within each enclosure, we created habitats with three different reed densities (zero, medium, and high). Tadpoles were placed in the enclosures and were followed for six weeks up to metamorphosis, during which we monitored water quality and phytoplankton composition. At the end of the experiment, tadpoles at medium and high reed densities developed more slowly than under the control. However, tadpole survival was similar across treatments. For a given developmental stage, total body length did not differ among treatments. Phytoplankton abundance varied with reed density, and groups known to be consumed by tadpoles were negatively influenced by reed density. We found no impact of reed density on pH, total phenolic concentration, or conductivity. Our results suggest that common reed establishment can influence amphibians with rapid development such as wood frogs. Though larval survival rates were similar across treatments, slower development under high reed densities implies a longer exposure to the risk of the pond drying out and to predators.