Projected Climate and Hydroregime Variability Constrain Ephemeral Wetland-Dependent Amphibian Populations in Simulations of Southern Toads

Abstract

Amphibian populations are threatened globally by stressors, including diminishing availabilityof suitable wetland breeding sites, altered hydroregimes driven by changing weather patterns,and exposure to contaminants. Ecological risk assessment should encompass spatial and temporalscales that capture influential ecological processes and demographic responses. Following thePopGUIDE framework of population model development for risk assessment, we used matrix populationmodels, in conjunction with existing hydroregime predictions, under a climate change scenarioto evaluate the effects of environmental stochasticity and aquatic pesticide exposure on amphibiansthat are dependent on ephemeral wetlands. Using southern toads (Anaxyrus terrestris) as an example,we simulated population dynamics with breeding success dependent on hydroregime suitability.Years were defined as optimal, marginal, or insufficient for successful toad recruitment, based on theduration of their potential breeding season and rate of larval development to metamorphosis. Wesimulated both probabilistic and chronologically specific population projections, including variableannual fecundity, based on hydroregime suitability and reduced larval survival from carbaryl exposure.In our simulations, populations were more negatively impacted by prolonged drought, andconsequently multiple sequential years of reproductive failure, than by aquatic pesticide exposure.These results highlight the necessity of reliable climate projections to accurately represent the effectsof altered hydroregimes on amphibian populations. Risk assessment approaches could be improvedwith flexible modifications that allow inclusion of various extrinsic stressors and identification ofdemographic and ecological vulnerabilities when precise data are lacking.

Citation

Awkerman, Jill A.; Greenberg, Cathryn H. 2022. Projected Climate and Hydroregime Variability Constrain Ephemeral Wetland-Dependent Amphibian Populations in Simulations of Southern Toads. Ecologies. 3(2): 235-248. https://doi.org/10.3390/ecologies3020018.