Abstract
AbstractFloodplain ponds and wetlands are productive and biodiverse ecosystems, yet they face multiple threats including altered hydrology, land use change, and non‐native species. Protecting and restoring important floodplain ecosystems requires understanding how organisms use these habitats and respond to altered environmental conditions. We developed Bayesian models to evaluate occupancy of six amphibian species across 103 off‐channel aquatic habitats in the Chehalis River floodplain, Washington State, USA. The basin has been altered by changes in land use, reduced river–wetland connections, and the establishment of non‐native American bullfrogs (Rana catesbeiana = Lithobates catesbeianus) and centrarchid fishes, all of which we hypothesized could influence native amphibian occupancy. Despite potential threats, the floodplain habitats had relatively high rates of native amphibian occupancy, particularly when compared to studies from non‐floodplain habitats within the species’ native ranges. The biggest challenge for native amphibians appears to be non‐native centrarchid fishes, which strongly reduced occupancy of two native amphibians: the northern red‐legged frog (Rana aurora) and the northwestern salamander (Ambystoma gracile). Emergent vegetative cover increased occupancy probability for all five native amphibian species, indicating that plant management may offer a strategy to counter the negative effect of centrarchids by providing refuge from predation. We found that temporary and permanent hydroperiod sites supported different species; hence, both should be conserved on the landscape. Lastly, human‐created and natural ponds had similar amphibian occupancy patterns, suggesting that pond construction offers a viable strategy for adding habitats to the floodplain landscape. Overall, floodplain ponds and wetlands provide important amphibian habitat, and we offer management strategies that will bolster amphibian occupancy in an altered floodplain landscape.
Highlights
Freshwater floodplains are among the most biodiverse and productive ecosystems on the planet (Junk et al 1989, Ward et al 1999, Tockner and Stanford 2002), providing ecosystem services valued at $1.5 trillion annually
We developed Bayesian occupancy models for the six amphibian species currently found within the floodplain and allowed for predator–prey interactions among amphibian species
We created detection and occupancy models starting with single-species, single-season occupancy models for the bullfrog and newt monitoring data. These two species potentially prey upon or compete with the other four native amphibian species; we developed their models first so that their modeled occupancy could be used in the detection and occupancy models for the other native species
Summary
Freshwater floodplains are among the most biodiverse and productive ecosystems on the planet (Junk et al 1989, Ward et al 1999, Tockner and Stanford 2002), providing ecosystem services valued at $1.5 trillion annually (de Groot et al 2012, Costanza et al 2014). Non-native fishes and bullfrogs introduced to the basin have potentially negative but unstudied ecological consequences To study this system, we developed Bayesian occupancy models for the six amphibian species currently found within the floodplain and allowed for predator–prey interactions among amphibian species. Detection bias is a major concern in systems where environmental conditions and species competition may influence both the probability of detecting a species (e.g., due to behavioral changes by the target species) and the probability that a species occurs at a site (Mackenzie et al 2017) We fit these models to three years of survey data from 103 off-channel habitats that represent oxbows, ponds, and seasonal wetlands. Our study was designed to inform aquatic restoration and management options for native amphibians in alluvial floodplains
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