Context
Climate change and anthropogenic stressors have contributed to rapid declines in biodiversity worldwide, particularly for amphibians. Amphibians play important ecological roles, yet little is known about how distribution hotspots may change or the factors influencing distribution patterns in the North American Great Plains.
Objectives
Ecological niche models improve understanding of biotic and abiotic factors associated with species' distributions and can highlight potential threats to species conservation. Here, we identify important predictors of amphibian distributions and predict how land use and climate change may alter distributions in the Upper Missouri River Basin.
Methods
We used publicly available occurrence data, 16 environmental and climatic predictors, and the machine-learning algorithm, Random Forests, to create spatially-explicit distribution models for eight amphibian species. Models were scored to current conditions (2005) and two future climate-change/land-use scenarios to predict changes in amphibian distributions for 2060.
Results
Models were highly accurate and revealed more pronounced distributional changes under the intensive RCP8.5/CONUS A2 scenario compared to the moderate RCP6.0/CONUS B2 scenario. Both scenarios predicted gains for most southeastern species (i.e., Blanchard’s cricket frogs, Plains leopard frogs, Woodhouse’s toads, and Great Plains toads) and declines for all western montane species. Overall, distribution changes were most influenced by climatic and geographic predictors, (e.g., summer temperature, precipitation, and elevation), and geography, versus anthropogenic land-use variables.
Conclusions
Changes in occurrence area varied by species and geography, however, high-elevation western species were more negatively impacted. Our distribution models provide a framework for future conservation efforts aiding the persistence of amphibian species across a warming, agriculturally dominated landscape.
Neonicotinoids are neurotoxic insecticides and are often
released
into nearby wetlands via subsurface tile drains and can negatively
impact nontarget organisms, such as amphibians. Previous studies have
indicated that imidacloprid, a commonly used neonicotinoid, can cross
the amphibian blood–brain barrier under laboratory conditions;
however, little is known about the impact of low concentrations in
a field-based setting. Here, we report aqueous pesticide concentrations
at wetland production areas that were either connected or not connected
to agricultural tile drains, quantified imidacloprid and its break
down products in juvenile amphibian brains and livers, and investigated
the relationship between imidacloprid brain concentration and brain
size. Imidacloprid concentrations in brain and water samples were
nearly 2.5 and 5 times higher at tile wetlands (brain = 4.12 ±
1.92 pg/mg protein; water = 0.032 ± 0.045 μg/L) compared
to reference wetlands, respectively. Tile wetland amphibians also
had shorter cerebellums (0.013 ± 0.001 mm), depicting a negative
relationship between imidacloprid brain concentration and cerebellum
length. The metabolite, desnitro-imidacloprid, had liver concentrations
that were 2 times higher at tile wetlands (2 ± 0.3 μg/g).
Our results demonstrate that imidacloprid can cross the amphibian
blood–brain barrier under ecological conditions and may alter
brain dimensions and provide insight into the metabolism of imidacloprid
in amphibians.
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