Observations of rapid colonization of constructed ponds by Western toad (Bufo boreas) in Oregon, USA
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Western North American Naturalist↗
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Bufo boreas Baird and Girard, 1852(b): western toad
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Book chapter↗
Between hot rocks and dry places: The status of the Dixie Valley toad
In Dixie Valley, Nevada, an isolated population of toads has been the subject of proactive conservation measures by the Nevada Department of Wildlife and the U.S. Fish and Wildlife Service since 2008 due to concerns about potential habitat degradation resulting from exploitation of nearby geothermal energy resources. These toads appear to belong within the Anaxyrus boreas species group but are commonly referred to as Dixie Valley toads (DVTs). The DVT is currently confined to an extremely narrow habitat range (370 ha) that is geographically isolated from any other A. boreas population. In this study, genetic variations in mitochondrial genes and 11 microsatellite loci were used to assess the affinities of DVTs in relation to members of the A. boreas species group. We compared results from DVTs with previously published data spanning much of the range of A. boreas in the United States and new data from a nearby toad population within Dixie Valley. Data from both mitochondrial DNA and microsatellites placed DVTs inside the A. boreas species group. In particular, DVTs fell into a cluster of A. boreas from Washington and California, along with other species from the A. boreas species group, namely A. nelsoni, A. canorus, and A. exsul. Genetic differentiation of DVTs was lowest between A. boreas populations in Washington and California. However, allele frequencies were significantly different between DVTs and all other populations, including a nearby locality within Dixie Valley. This genetic differentiation, along with the DVT's geographical isolation and restricted habitat, warrants recognition of the DVT as a distinct management unit.
Nevada↗
Effects of ultraviolet radiation on toad early life stages
Background Exposure to harmful levels of ultraviolet-B radiation (UVB), a component of solar radiation, has been suggested as a potential cause of amphibian declines. Methods We measured solar radiation (UVB, ultraviolet-A, and visible) wavebands in breeding ponds of Bufo boreas (boreal toad, a montane species that has undergone severe population declines) and Bufo woodhousii (Woodhouse’s toad, a plains toad that has not experienced declines) and examined tolerances of these species to simulated solar UVB exposures in the laboratory. Results We found larvae of both species to be tolerant of simulated solar UVB in excess of solar UVB levels observed in their breeding ponds. B. boreas tadpoles were more tolerant of simulated solar UVB exposure than B. woodhousii tadpoles, possibly because of greater amounts of photoprotective melanin in B. boreas skin. Conclusions UVB levels observed in B. boreas habitats do not currently appear to constitute a threat to the survival of these animals; however, long-term (>1 month) exposure to UVB levels comparable to levels associated with the water interface appears to reduce survival in B. woodhousii tadpoles. Therefore, future increases in surface and water column UVB radiation in bufonid habitats might pose significant survival risks to B. boreas or B. woodhousii populations.
Environmental Science and Pollution Research↗
Effects of ultraviolet radiation on boreal toads in Colorado
Field exposures of Bufo boreas embryos to fractions of ambient UV-B radiation at two sites in Rocky Mountain National Park, Colorado, USA, were conducted to evaluate UV-B as a possible cause of recent severe declines of this species. There were no differences in hatching success of B. boreas embryos exposed to 0–100% of ambient UV-B radiation at either study site, results that are different from those of recent studies in Oregon that found increased mortality of B. boreas embryos exposed to ambient UV-B. The reasons for these differing results are not apparent, and several possible explanations exist, including differences in experimental design, presence or absence of a pathogenic fungus, and geographic genetic variation. Bufo boreas embryos were probably not receiving higher doses of UV-B radiation during the experiments in Oregon compared to the experiments in this study. Results of this study do not support UV-B radiation alone as the cause of the decline of B. boreas during the past 20 yr in the southern Rocky Mountains, but UV-B cannot be dismissed because of the contradictory results from other studies.
Colorado↗
A model to inform management actions as a response to chytridiomycosis-associated decline
Decision-analytic models provide forecasts of how systems of interest will respond to management. These models can be parameterized using empirical data, but sometimes require information elicited from experts. When evaluating the effects of disease in species translocation programs, expert judgment is likely to play a role because complete empirical information will rarely be available. We illustrate development of a decision-analytic model built to inform decision-making regarding translocations and other management actions for the boreal toad (Anaxyrus boreas boreas), a species with declines linked to chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd). Using the model, we explored the management implications of major uncertainties in this system, including whether there is a genetic basis for resistance to pathogenic infection by Bd, how translocation can best be implemented, and the effectiveness of efforts to reduce the spread of Bd. Our modeling exercise suggested that while selection for resistance to pathogenic infection Decision-analytic models provide forecasts of how systems of interest will respond to management. These models can be parameterized using empirical data, but sometimes require information elicited from experts. When evaluating the effects of disease in species translocation programs, expert judgment is likely to play a role because complete empirical information will rarely be available. We illustrate development of a decision-analytic model built to inform decision-making regarding translocations and other management actions for the boreal toad ( Anaxyrus boreas boreas ), a species with declines linked to chytridiomycosis caused by Batrachochytrium dendrobatidis ( Bd ). Using the model, we explored the management implications of major uncertainties in this system, including whether there is a genetic basis for resistance to pathogenic infection by Bd , how translocation can best be implemented, and the effectiveness of efforts to reduce the spread of Bd . Our modeling exercise suggested that while selection for resistance to pathogenic infection by Bd could increase numbers of sites occupied by toads, and translocations could increase the rate of toad recovery, efforts to reduce the spread of Bd may have little effect. We emphasize the need to continue developing and parameterizing models necessary to assess management actions for combating chytridiomycosis-associated declines. by Bd could increase numbers of sites occupied by toads, and translocations could increase the rate of toad recovery, efforts to reduce the spread of Bd may have little effect. We emphasize the need to continue developing and parameterizing models necessary to assess management actions for combating chytridiomycosis-associated declines.
EcoHealth↗
Survey and assessment of amphibian populations in Rocky Mountain National Park
We conducted surveys in Rocky Mountain National Park, Colorado for amphibians in 1987-1994. Four species, Ambystoma tigrinum, Bufo boreas, Pseudacris maculata, and Rana sylvatica , were recorded. Pseudacris maculata was the most widely distributed and abundant species in the Park. Two populations of E maculata were estimated to contain 161 and 136 breeding males in 1988. There was no evidence of a decline of A. tigrinum or R. sylvatica , but these species were found at relatively few locations. We did not detect Rana pipiens , which had been known previously from 3 locations in the Park. We found 7 breeding populations of B. boreas , which has declined recently elsewhere in the southern Rocky Mountains, but all but 2 of these populations were small and may not reproduce annually. At least one of these small populations is thought to have been extirpated. Estimated numbers of males in the 2 large populations, which are 6.4 km apart in the same drainage, were stable or increasing slightly from 1992 to 1995, averaging 189 and 239 individuals. Current and known locations of amphibians did not differ in elevation, size, lake type, presence of shallow water or emergent vegetation on the north shore, or presence of trout. Water chemistry at amphibian breeding sites was variable, but pH decreased significantly with increasing elevation. Causes of declines of B. boreas and R. pipiens are not known. Populations of B. boreas in the North Fork of the Big Thompson River are critically important to the conservation of this species in the Rocky Mountains.
Colorado↗
Moss and lichen cover mapping at local and regional scales in the boreal forest ecosystem of central Canada
Mosses and lichens are important components of boreal landscapes [Vitt et al., 1994; Bubier et al., 1997]. They affect plant productivity and belowground carbon sequestration and alter the surface runoff and energy balance. We report the use of multiresolution satellite data to map moss and lichens over the BOREAS region at a 10 m, 30 m, and 1 km scales. Our moss and lichen classification at the 10 m scale is based on ground observations of associations among soil drainage classes, overstory composition, and cover type among four broad classes of ground cover (feather, sphagnum, and brown mosses and lichens). For our 30 m map, we used field observations of ground cover-overstory associations to map mosses and lichens in the BOREAS southern study area (SSA). To scale up to a 1 km (AVHRR) moss map of the BOREAS region, we used the TM SSA mosaics plus regional field data to identify AVHRR overstory-ground cover associations. We found that: 1) ground cover, overstory composition and density are highly correlated, permitting inference of moss and lichen cover from satellite-based land cover classifications; 2) our 1 km moss map reveals that mosses dominate the boreal landscape of central Canada, thereby a significant factor for water, energy, and carbon modeling; 3) TM and AVHRR moss cover maps are comparable; 4) satellite data resolution is important; particularly in detecting the smaller wetland features, lakes, and upland jack pine sites; and 5) distinct regional patterns of moss and lichen cover correspond to latitudinal and elevational gradients. Copyright 2001 by the American Geophysical Union.
Journal of Geophysical Research D: Atmospheres↗
Thermal conditions predict intraspecific variation in senescence rate in frogs and toads
Variation in temperature is known to influence mortality patterns in ectotherms. Even though a few experimental studies on model organisms have reported a positive relationship between temperature and actuarial senescence (i.e., the increase in mortality risk with age), how variation in climate influences the senescence rate across the range of a species is still poorly understood in free-ranging animals. We filled this knowledge gap by investigating the relationships linking senescence rate, adult lifespan, and climatic conditions using long-term capture–recapture data from multiple amphibian populations. We considered two pairs of related anuran species from the Ranidae ( Rana luteiventris and Rana temporaria ) and Bufonidae ( Anaxyrus boreas and Bufo bufo ) families, which diverged more than 100 Mya and are broadly distributed in North America and Europe. Senescence rates were positively associated with mean annual temperature in all species. In addition, lifespan was negatively correlated with mean annual temperature in all species except A. boreas . In both R. luteiventris and A. boreas , mean annual precipitation and human environmental footprint both had negligible effects on senescence rates or lifespans. Overall, our findings demonstrate the critical influence of thermal conditions on mortality patterns across anuran species from temperate regions. In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline.
Proceedings of the National Academy of Sciences↗
U-Th-Pb systematics of some granitoids from the northeastern Yilgarn Block, Western Australia and implications for uranium source rock potential
The Mount Boreas‐type granite and spatially associated syenitic granitoid of Western Australia yield Pb‐Pb ages of 2370 ± 100 Ma and 2760 ± 210 Ma, respectively. Th‐Pb ages, although less precise, are concordant with these ages, and therefore the apparent ages are interpreted to be the crystallisation ages for these two units. U‐Pb ages are variable and for the most part anomalously old, which suggests a Cainozoic uranium loss. However, this loss is generally small (< 3 μ g/g); therefore, neither granitoid in its fresh state provides a good source for nearby calcrete‐hosted uranium deposits. The possibility remains that the Mount Boreas‐type granite that has been completely weathered during the Tertiary could have been a source for the calcrete‐type uranium deposits in W.A. Although the Mount Boreas‐type granite is highly fractionated, it does not bear a strong geochemical imprint of a sedimentary precursor. This feature contrasts it with apparently fresh granitoids from other parts of the world that have lost large amounts of uranium (∼ 20 μ g/g ) and are associated with large roll‐type and other low temperature‐type uranium deposits.
Journal of the Geological Society of Australia↗
Host-pathogen metapopulation dynamics suggest high elevation refugia for boreal toads
Emerging infectious diseases are an increasingly common threat to wildlife. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis ( Bd ), is an emerging infectious disease that has been linked to amphibian declines around the world. Few studies exist that explore amphibian- Bd dynamics at the landscape scale, limiting our ability to identify which factors are associated with variation in population susceptibility and to develop effective in situ disease management. Declines of boreal toads ( Anaxyrus boreas boreas ) in the Southern Rocky Mountains are largely attributed to chytridiomycosis but variation exists in local extinction of boreal toads across this metapopulation. Using a large-scale historic dataset, we explored several potential factors influencing disease dynamics in the boreal toad- Bd system: geographic isolation of populations, amphibian community richness, elevational differences, and habitat permanence. We found evidence that boreal toad extinction risk was lowest at high elevations where temperatures may be sub-optimal for Bd growth and where small boreal toad populations may be below the threshold needed for efficient pathogen transmission. In addition, boreal toads were more likely to recolonize high elevation sites after local extinction, again suggesting that high elevations may provide refuge from disease for boreal toads. We illustrate a modeling framework that will be useful to natural resource managers striving to make decisions in amphibian- Bd systems. Our data suggest that in the southern Rocky Mountains high elevation sites should be prioritized for conservation initiatives like reintroductions.
Ecological Applications↗
Wildfire influences individual growth and breeding dispersal, but not survival and recruitment in a montane amphibian
Global wildfire regimes are changing rapidly, with widespread increases in the size, frequency, duration, and severity of wildfires. Whereas the effects of wildfire on ecological state variables such as occupancy, abundance, and species diversity are relatively well documented, changes in population vital rates (e.g., survival, recruitment) and individual responses (e.g., growth, movement) to wildfire are more limited because of the detailed information needed on the same individuals both pre- and post-fire. We capitalized on the 2018 Roosevelt wildfire, which occurred during our 6-year (2015–2020) capture–mark–recapture study of boreal toads ( Anaxyrus boreas boreas ; n = 1415) in the Bridger-Teton National Forest, USA, to evaluate the responses of population vital rates and individual metrics to wildfire. We employed robust design capture–recapture models to compare the growth, dispersal, survival, and recruitment of adult boreal toads pre- and post-fire at burned versus unburned sites. At burned locations, growth increased 2 years post-fire compared with the year directly following wildfire and was higher 2 years post-fire than any other interval during our study period. Boreal toads dispersed to alternative breeding patches more at burned sites than unburned sites and dispersal increased 2 years post-fire compared with the year directly following wildfire. Annual survival and recruitment neither differed between pre- and post-fire years nor among pre-fire years, the year following wildfire, and 2 years post-fire. We demonstrate that, in certain contexts, dispersal can play a major role in changes to state variables (e.g., abundance) after wildfire, as opposed to other vital rates such as survival and recruitment. Our study represents an important step toward understanding the biological processes that underlie observed patterns in state variables following wildfire, which ultimately will be critical for the effective management of species in landscapes experiencing shifts in fire activity.
Wyoming↗
Density as a mechanism linking habitat disturbance to increased pathogen prevalence: Evidence from a natural experiment
Sudden habitat loss associated with environmental disturbance can trigger animals to move from affected to undisturbed areas, where increases in local density may occur. Although pathogen transmission is strongly related to local density, how crowding after habitat loss affects infection dynamics in wild populations remains unclear. Here we conceptualize the Disturbance-Density-Disease hypothesis, which posits that disturbance-induced habitat loss results in increased pathogen prevalence via increases in local density at adjacent, undisturbed patches. We then used data from before, during, and after flooding disturbance to test this hypothesis in boreal toads Anaxyrus boreas boreas co-occurring with the pathogenic fungus Batrachochytrium dendrobatidis ( Bd ). We collected Bd samples from captured individuals during a 5-year (2015–2019) mark-recapture study of boreal toads ( n = 1295) that breed in beaver ponds in western Wyoming, USA. During spring of 2017, an extreme flooding event destroyed several beaver dams, resulting in the loss of breeding habitat. We compared host density and pathogen prevalence pre- and post-disturbance at sites affected versus unaffected by flooding. At affected sites, population density and Bd prevalence increased at adjacent, undisturbed ponds following the sudden loss of habitat. Moreover, neither host density nor Bd prevalence increased at control sites in areas unaffected by flooding. Taken together, our results support hypothesized links between disturbance, adjacent increases in density, and subsequent increases in pathogen prevalence. Our study contributes to a growing body of ecological research leveraging natural experiments to extract insights from extreme disturbance events. By doing so, we demonstrate an important consequence of disturbance beyond proximate habitat loss and introduce a clear conceptual approach (the Disturbance-Density-Disease hypothesis) to understanding how pathogen transmission can be affected by disturbance via alterations to local density.
Wyoming↗