As natural wetlands disappear, constructed wetlands may play vital roles in amphibian conservation. However, previous investigations have concluded that artificial wetlands do not adequately replace lost wildlife habitat. Nevertheless, constructed wetlands serve as breeding habitat for amphibians where extensive natural wetland loss has occurred. To investigate the roles of engineered wetland features on amphibian abundance, we surveyed 49 constructed wetlands throughout northern Missouri. Cricket frogs (Acris crepitans), bullfrogs (Lithobates catesbeianus), and leopard frogs (Lithobates blairi/sphenocephalus complex) each occurred in over 80% of surveyed wetlands. Salamanders and hylid frogs were rarely encountered. We used an information theoretic approach to examine relationships between individual species and habitat features associated with wetland designs and placements. We found that models incorporating design features of open water ponds best explained abundances of most commonly encountered species. At the placement level, models that included nearby aquatic habitat ranked highest for common species. Salamanders and most hylid frogs responded positively to aquatic vegetative cover but negatively to fish abundance and anthropogenic disturbance-related features in the landscape. Our results indicate that to be effective amphibian conservation tools, constructed wetlands should be fish-free, heavily vegetated, include shallows, and placed within areas of low anthropogenic disturbance.

Summary1. Restored and constructed habitats can play important conservation roles. Predators help shape communities in these habitats through complex interactions with prey, other predators and biotic and abiotic characteristics of the environment. However, introduced predators can have dramatic effects that may be difficult to predict. 2. Using regression models, we compared influences of introduced invasive western mosquitofish Gambusia affinis to those of two naturally colonizing predators (crayfish and dragonflies), and vegetation, on three anuran species in experimentally constructed wetlands. Using analyses of covariance, we also examined influences of mosquitofish and vegetation on aquatic invertebrate communities. 3. We found that mosquitofish reduced abundances of grey treefrogs Hyla versicolor and H. chrysoscelis and boreal chorus frog Pseudacris maculata, but had no significant influence on green frog Lithobates clamitans. Mosquitofish also reduced invertebrate abundance, but their effect on richness was less clear. Vegetation cover did not significantly increase most anuran or invertebrate abundances. However, vegetation increased invertebrate richness. After fish removal, invertebrate abundance increased. Fish removal may have facilitated chorus frog re-colonization into wetlands with low abundance of invertebrate predators. 4. Our results indicate that mosquitofish are detrimental to wetland communities, and we recommend that managers avoid stocking mosquitofish. We also encourage temporary or drainable wetlands to prevent mosquitofish persistence if colonization occurs. Implementing these recommendations will improve the conservation potential of restored wetlands.

Aquatic habitat features can directly influence the abundance, species richness, and quality of juvenile amphibians recruited into adult populations. We examined the influences of within-wetland slope, vegetation, and stocked mosquito fish (Gambusia affinis) on amphibian metamorph production and species richness during the first two years post-construction at 18 experimental wetlands in northeast Missouri (U.S.A.) grasslands. We used an information theoretic approach (AICc) to rank regression models representing total amphibian metamorph production, individual amphibian species metamorph production, and larval amphibian species richness. Total amphibian metamorph production was greatest at shallow-sloped, fish-free wetlands during the first year, but shallow-sloped wetlands with high vegetation cover were best the second year. Species richness was negatively associated with fish and positively associated with vegetation in both survey years. Leopard frog (Rana blairi/sphenocephala complex) metamorph quality, based on average metamorph size, was influenced by slope and the number of cohorts in the wetland. However, the tested variables had little influence on the size of American toads (Bufo americanus) or boreal chorus frogs (Pseudacris maculata). Our results indicate that wetlands designed to act as functional reproductive habitat for amphibians should incorporate shallows, high amounts of planted or naturally established vegetation cover, and should be fish-free.

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