(ARMI) changing a filter in an air sampler that is used to measure agricultural chemicals that drift into Yosemite NP, California. Photo by: J. Fellers.
Declines in amphibian populations have occurred not only on areas clearly impacted by human activities such as urbanization, but also on protected lands intended to buffer amphibians and other wildlife from anthropogenic disturbances. Some stressors are not stopped by preserve boundaries and can affect wildlife populations 10's or 100's of kilometers from their source or point of use. For example, pesticides, fertilizers, or supplements given to livestock can be transported from the terrestrial setting where they are applied, to aquatic environments via precipitation, run-off, erosion, wind, and misuse. Conversely, some contaminants such as mercury or selenium occur naturally, but can be concentrated, or disturbed and released into the environment by human activities. Amphibian populations can be exposed to multiple stressors simultaneously, producing novel conditions with unknown outcomes.
ARMI scientists conduct research to identify stressors and evaluate their impacts on amphibian individuals and populations.
ARMI Products on Stressors
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Even with forewarning, challenges remain in developing a proactive response to emerging infectious diseases
Authors: Grant EHC, Muths E, Katz RA, Canessa S, Adams MJ, Ballard JR, Berger L, Briggs CJ, Coleman JH, Gray MJ, Harris MC, Harris RN, Hossack B, Huyvaert KP, Kolby J, Lips KR, Lovich RE, McCallum HI, Mendelson III JR, Nanjappa P, Olson DH, Powers JG, Richgels KLD, Russell RE, Schmidt BR | Outlet: Frontiers in Ecology and Evolution
Despite calls for improving responses to emerging infectious diseases of wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive, management framework can identify immediate actions that reduce future impacts even before a disease is detected, as well as prepare actions conditional on disease emergence. We identify four main challenges to developing proactive management strategies for the newly discovered salamander pathogen, Batrachochytrium salamandrivorans (Bsal). Given that deep uncertainty is a hallmark of wildlife disease management and decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs among proactive (pre-emergence) and reactive (post-emergence) management. Using principles from decision analysis, natural resources agencies and policy-makers can utilize a variety of tools to improve the development of management strategies for emerging infectious diseases.
Large-scale recovery of an endangered amphibian despite ongoing exposure to multiple stressors
Authors: Knapp RA, Fellers GM, Kleeman PM, Miller DAW, Vredenburg VT, Rosenblum EB, Briggs CJ | Date: 2016-10-03 | Outlet: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1600983113 | Format: .PDF
Amphibians are one of the most threatened animal groups, with 32% of species at risk of extinction. Given this, is the disappearance of a large fraction of the Earth’s amphibians inevitable, or are some declining species more resilient than is generally assumed? We address this question in a species that is emblematic of many declining amphibians, the endangered Sierra Nevada yellow-legged frog (Rana sierrae). Based on >7,000 frog surveys conducted across Yosemite National Park over a 20-year period, we show that after decades of decline and despite ongoing exposure to multiple stressors including introduced fish, the recently emerged disease chytridiomycosis, and pesticides, R. sierrae abundance increased 7-fold during the study and at a rate of 11% per year. These increases occurred in hundreds of populations throughout Yosemite, providing a rare example of amphibian recovery at an ecologically relevant spatial scale. Results from a laboratory experiment indicate that these increases may be due in part to reduced frog susceptibility to chytridiomycosis. The disappearance of nonnative fish from numerous water bodies following cessation of stocking also contributed to the recovery. The large-scale increases in R. sierrae abundance we document suggest that when habitats are relatively intact and stressors are reduced in their importance by active management or species’ adaptive responses declines of some amphibian may be partially reversible, at least at a regional scale. Other studies conducted over similarly large temporal and spatial scales are critically needed to provide insight and generality about the reversibility of amphibian declines at a global scale.
Potential Interactions Among Disease, Pesticides, Water Quality and Adjacent Land Cover in Amphibian Habitats in the United States
Authors: Battaglin W, Smalling K, Anderson C, Calhoun D, Chestnut T, Muths E | Date: 2016-05-24 | Outlet: Science of the Total Environment 320-332
To investigate interactions among disease, pesticides, water quality and adjacent land cover we collected samples of water, sediment, and frog tissue from 21 sites in 7 States in the United States (US) representing a variety of amphibian habitats. All samples were analyzed for > 90 pesticides and pesticide degradates, and water and frogs were screened for the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) using molecular methods. Pesticides and pesticide degradates were detected frequently in frog breeding habitats (water and sediment) as well as in frog tissue. Fungicides occurred more frequently in water, sediment, and tissue than was expected based upon their limited use relative to herbicides or insecticides. Pesticide occurrence in water or sediment was not a strong predictor of occurrence in tissue, but pesticide concentrations in tissue were correlated positively to agricultural and urban land, and negatively to forested land in 2-kilometer buffers around the sites. Bd was detected in water at 45% of sites, and on 34% of swabbed frogs. Bd detections in water were not associated with differences in land use around sites, but sites with detections had colder water. Frogs that tested positive for Bd were associated with sites that had higher total fungicide concentrations in water and sediment, but lower insecticide concentrations in sediments relative to frogs that were Bd negative. Bd concentrations on frog swabs were positively correlated to dissolved organic carbon, and total nitrogen and phosphorus, and negatively correlated to pH and water temperature.
Data were collected from a range of locations and amphibian habitats and represent some of the first field-collected information aimed at understanding the interactions between pesticides, land use, and amphibian disease. These interactions are of particular interest to conservation efforts as many amphibians live in altered habitats and may depend on wetlands embedded in these landscapes to survive.