Stressors

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.

Gary Fellers, air quality
ARMI biologist Gary Fellers changing a filter in an air sampler that is used to measure agricultural chemicals that drift into Yosemite NP, California. Photo by: J. Fellers.

Stressors - ARMI Papers & Reports

Sampling for stream salamanders
Sampling for stream salamanders
EHC Grant
Papers & Reports A National-Scale Assessment of Mercury Bioaccumulation in United 2 States National Parks Using Dragonfly Larvae As Biosentinels 3 through a Citizen-Science Framework
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Authors: Eagles-Smith CA, Willaker JJ, Nelson SJ, Flanagan CM, Krabbenhoft DP, Chen CY, Ackerman JT, Grant EHC, Pilliod D | Outlet: Environmental Science and Technology
ABSTRACT: We conducted a national-scale assessment of mercury (Hg) bioaccumulation in aquatic ecosystems using dragonfly
larvae as biosentinels by developing a citizen-science network to facilitate biological sampling. Implementing a carefully designed
sampling methodology for citizen scientists, we developed an effective framework for a landscape-level inquiry that might otherwise
be resource limited. We assessed the variation in dragonfly Hg concentrations across >450 sites spanning 100 United States National
Park Service units and examined intrinsic and extrinsic factors associated with the variation in Hg concentrations. Mercury
concentrations ranged between 10.4 and 1411 ng/g of dry weight across sites and varied among habitat types. Dragonfly total Hg
(THg) concentrations were up to 1.8-fold higher in lotic habitats than in lentic habitats and 37% higher in waterbodies, with
abundant wetlands along their margins than those without wetlands. Mercury concentrations in dragonflies differed among families
but were correlated (R2 > 0.80) with each other, enabling adjustment to a consistent family to facilitate spatial comparisons among
sampling units. Dragonfly THg concentrations were positively correlated with THg in both fish and amphibians from the same
locations, indicating that dragonfly larvae are effective indicators of Hg bioavailability in aquatic food webs. Collectively, this
continental-scale study demonstrates the utility of dragonfly larvae for estimating the potential mercury risk to fish and wildlife in
aquatic ecosystems and provides a framework for engaging citizen science as a component of landscape Hg monitoring programs.
Juvenile California newt ([I]Taricha torosa[/I]) from southern California.  The larval stage is very sensitive to rainfall and water availability.
Juvenile California newt (Taricha torosa) from southern California. The larval stage is very sensitive to rainfall and water availability.
USGS
Papers & Reports Amphibian responses in the aftermath of extreme climate events
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Authors: Bucciarelli G M, Clark M, Delaney K S, Riley S P D, Shaffer H B, Fisher R N, Honeycutt R L, Kats L B | Date: 2020-02-25 | Outlet: Scientific Reports 10:3409 | Format: .PDF
Climate change-induced extinctions are estimated to eliminate one in six known species by the end
of the century. One major factor that will contribute to these extinctions is extreme climatic events.
Here, we show the ecological impacts of recent record warm air temperatures and simultaneous peak
drought conditions in California. From 2008–2016, the southern populations of a wide-ranging endemic
amphibian (the California newt, Taricha torosa) showed a 20% reduction to mean body condition and
significant losses to variation in body condition linked with extreme climate deviations. However,
body condition in northern populations remained relatively unaffected during this period. Range-wide
population estimates of change to body condition under future climate change scenarios within the
next 50 years suggest that northern populations will mirror the loss of body condition recently observed
in southern populations. This change is predicated on latter 21st century climate deviations that
resemble recent conditions in Southern California. Thus, the ecological consequences of climate change
have already occurred across the warmer, drier regions of Southern California, and our results suggest
that predicted climate vulnerable regions in the more mesic northern range likely will not provide
climate refuge for numerous amphibian communities.
Papers & Reports Amphibian chytrid prevalence on boreal toads in SE Alaska and NW British Columbia: tests of habitat, life stages, and temporal trends
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Authors: Hossack BR, Adams MJ, Honeycutt RK, Belt JJ, Pyare S | Date: 2020 | Outlet: Diseases of Aquatic Organisms 137:159-165
Tracking and understanding variation in pathogens such as Batrachochytrium dendrobatidis
(Bd), the agent of amphibian chytridiomycosis, which has caused population declines
globally, is a priority for many land managers. However, relatively little sampling of amphibian
communities has occurred at high latitudes. We used skin swabs collected during 2005?2017 from
boreal toads Anaxyrus boreas (n = 248), in southeast Alaska (USA; primarily in and near Klondike
Gold Rush National Historical Park [KLGO]) and northwest British Columbia (Canada) to determine
how Bd prevalence varied across life stages, habitat characteristics, local species richness,
and time. Across all years, Bd prevalence peaked in June and was >3 times greater for adult toads
(37.5%) vs. juveniles and metamorphs (11.2%). Bd prevalence for toads in the KLGO area, where
other amphibian species are rare or absent, was highest from river habitats (55.0%), followed by
human-modified upland wetlands (32.3%) and natural upland wetlands (12.7%)—the same rankorder
these habitats are used for toad breeding. None of the 12 Columbia spotted frogs Rana
luteiventris or 2 wood frogs R. sylvatica from the study area tested Bd-positive, although all were
from an area of low host density where Bd has not been detected. Prevalence of Bd on toads in the
KLGO area decreased during 2005?2015. This trend from a largely single-species system may be
encouraging or concerning, depending on how Bd is affecting vital rates, and emphasizes the
need to understand effects of pathogens before translating disease prevalence into management
actions.
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