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Papers & Reports Looking ahead, guided by the past: The role of U.S. national parks in amphibian research and conservation
Authors: Brian J Halstead; Andrew M Ray; Erin Muths; Evan HC Grant; Rob L Grasso; Michael J Adams; Katy S Delaney; Jane Carlson; Blake R Hossack
Date: 2022-03 | Outlet: Journal of Ecological Indicators 136: 108631
Protected areas like national parks are essential elements of conservation because they limit human influence on the landscape, which protects biodiversity and ecosystem function. The role of national parks in conservation, however, often goes far beyond limiting human influence. The U.S. National Park Service and its system of land units contribute substantively to conservation by providing protected lands where researchers can document trends in species distributions and abundances, examine characteristics important for generating these trends, and identify and implement conservation strategies to preserve biodiversity. We reviewed the contribution of U.S. national parks to amphibian research and conservation and highlight important challenges and findings in several key areas. First, U.S. national parks were instrumental in providing strong support that amphibian declines were real and unlikely to be simply a consequence of habitat loss. Second, research in U.S. national parks provided evidence against certain hypothesized causes of decline, like UV-B radiation, and evidence for others, such as introduced species and disease. However, describing declines and identifying causes contributes to conservation only if it leads to management; importantly, U.S. national parks have implemented many conservation strategies and evaluated their effectiveness in recovering robust amphibian populations. Among these, removal of invasive species, especially fishes; conservation translocations; and habitat creation and enhancement stand out as examples of successful conservation strategies with broad applicability. Successful management for amphibians is additionally complicated by competing mandates and stakeholder interests; for example, past emphasis on increasing visitor enjoyment by introducing fish to formerly fishless lakes had devastating consequences for many amphibians. Other potential conflicts with amphibian conservation include increasing development, increased risk of introductions of disease and exotic species with increased visitation, and road mortality. Decision science and leveraging partnerships have proven to be key components of effective conservation under conflicting mandates in national parks. As resource managers grapple with large-scale drivers that are outside local control, public-private partnerships and adaptive strategies are increasing in importance. U.S. national parks have played an important role in many aspects of identifying and ameliorating the amphibian decline crisis and will continue to be essential for the conservation of amphibians in the future.
Papers & Reports Population Dynamics of the Threatened Oregon Spotted Frog (Rana pretiosa) Before and After Drought Mitigation
Authors: Jennifer C Rowe; Christopher A Pearl; Adam Duarte; Brome McCreary; Michael J Adams
Date: 2023-09-22 | Outlet: The Journal of Wildlife Management
Amphibians are among the most sensitive taxa to climate change, and species inhabiting arid and semiarid landscapes at the extremes of their range are especially vulnerable to drought. The Jack Creek, Oregon, USA, population of Oregon spotted frogs (Rana pretiosa) faces unique challenges because it occupies the highest elevation site in the species' extant range and one that has been transformed by loss of American beavers (Castor canadensis[/]), which historically maintained open water. We evaluated the effects of drought mitigation (addition of excavated ponds) on relationships between local and regional water availability, inactive legacy beaver dams, and Oregon spotted frog population dynamics in the Jack Creek system. We conducted egg mass surveys and capture-mark-recapture sampling at a treatment reach with excavated ponds and 3 reference reaches over 13 years; surveys spanned a period before and after pond excavation at the treatment and 1 primary comparison reference reach. We analyzed data using a combination of robust design capture-mark-recapture estimators and generalized linear mixed models to characterize population dynamics. Adult Oregon spotted frog survival was approximately 19.5% higher at the treatment reach than the primary reference reach during the study period. Annual survival was most strongly associated with late summer vegetation greenness, a proxy for water availability, and males had higher survival than females. Among the 4 study reaches, the treatment reach consistently had higher late summer vegetation greenness, and the hydrology functioned more independently of regional precipitation patterns relative to the reference reaches; however, these dynamics were not linked to pond excavation. Breeding was concentrated in 2 legacy beaver ponds that were deepened by excavation during the study compared to an unexcavated beaver pond, 2 excavated ponds without legacy beaver dams, and 9 reference ponds. These results point to the benefit of enhancing existing beaver structures and indicate that management actions aimed at maintaining surface water for breeding in spring and saturated soils and ponded water for adults in late summer would benefit this unique population of Oregon spotted frogs in the face of drought.
Papers & Reports ANAXYRUS MONFONTANUS (Hot Creek Toad). REPRODUCTION
Authors: Patrick M Kleeman
Date: 2023-09 | Outlet: Herpetological Review
A natural history note describing a late season breeding event by Hot Creek Toads following monsoonal rains.
Papers & Reports Research Needs to Inform Amphibian Conservation in the Anthropocene
Authors: Evan HC Grant; Staci M Amburgey; Brian Gratwicke; Victor Acosta Chaves; Anat M Belasen; David Bickford; Carsten Bruhl; Natalie E Calatayud; Nick Clemann; Simon Clulow; Jeff Dawson; David A DeAngelis; Kenneth C Dodd; Annette Evans; Gentile Francesco Ficetola; Mattia Falaschi; Sergio Gonzalez-Mollinedo; D M Green; Roseanna Gamlen-Greene; Richard A Griffiths; Brian J Halstead; Craig Hassapakis; Geoffrey Heard; Catharina Karlsson; Tom Kirschey; Brittany A Kosch; Sophia Kusterko Novaes; Luke Linhoff; John C Maerz; Brittany A Mosher; Katherine M O'Donnell; Leticia M Ochoa-Ochoa; J D Roberts; A Silla; Tariq Stark; Jeanne Tarrant; R Upton; Judit Voros; Erin Muths
Date: 2023 | Outlet: Conservation Science and Practice
The problem of global amphibian declines has prompted extensive research over the last three decades; initially the focus was on identifying and characterizing the extent of the problem, but more recently efforts have shifted to evidence-based research designed to improve conservation outcomes. Using input from participants at the 9th World Congress of Herpetology, a US Geological Survey Powell Center symposium, amphibian listservs, the IUCN Assisted Reproductive Technologies and Gamete Biobanking group, and respondents to a survey, we developed a list of 25 priority research questions for amphibian conservation at this stage of the Anthropocene. These research needs represent critical knowledge gaps for amphibian conservation.
Papers & Reports Sierra Nevada amphibians demonstrate stable occupancy despite precipitation volatility in the early 21st Century
Authors: Brian J Halstead; Patrick M Kleeman; Jonathan P Rose; Gary M Fellers
Date: 2023-02-07 | Outlet: Frontiers in Ecology and Evolution
Climate can have a strong influence on species distributions, and amphibians with different life histories might be affected by annual variability in precipitation in different ways. The Sierra Nevada of California, United States, experienced some of the driest and wettest years on record in the early 21st Century, with variability in annual precipitation predicted to increase with climate change. We examined the relationship between adult occupancy dynamics of three high elevation anurans and site and annual variation in measures of winter severity, summer wetness, and cumulative drought. We further evaluated how these weather conditions affected the probability that each species would reproduce, conditional on their occurrence at a site. We found that although different aspects of weather affected the occupancy dynamics of each species differently, adult occupancy probabilities were generally stable throughout our 15-year study period. The probability of reproduction, although slightly more variable than adult occupancy, was similarly stable throughout the study. Although occurrence of the three species was resilient to recent extremes in precipitation, more detailed demographic study would inform the extent to which amphibian populations will remain resilient to increasing severity, duration, and frequency of drought and flood cycles.
Papers & Reports Keeping the Heat On: Weighted Surveillance for Chytrid Fungus in Dixie Valley Toads
Authors: Matthew J Forrest; Brian J Halstead; Daniel A Grear; Patrick M Kleeman; Brian D Todd; Oliver J Miano; Kris Urquhart
Date: 2023-07-24 | Outlet: Journal of Wildlife Diseases
Introduced fungal pathogens have caused declines and extinctions of naive wildlife populations across vertebrate classes. Consequences of introduced pathogens to hosts with small ranges might be especially severe because of limited redundancy to rescue populations and lower abundance that may limit the resilience of populations to perturbations like disease introduction. As a complement to biosecurity measures to prevent the spread of pathogens, surveillance programs may enable early detection of pathogens, when management actions to limit the effects of pathogens on naïve hosts might be most bene?cial. We analyzed surveillance data for the endangered and narrowly endemic Dixie Valley toad (Anaxyrus [= Bufo] williamsi) from two time periods (2011–2014 and 2019–2021) to estimate the minimum detectable prevalence of the amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd). We assessed if detection ef?ciency could be improved by using samples from both Dixie Valley toads and co-occurring introduced American bullfrogs (Lithobates catesbeianus) and literature-derived surveillance weights. We further evaluated a weighted surveillance design to increase the efficiency of surveillance efforts for Bd within the toad’s small (<6km2) range. We found that monitoring adult and larval American bullfrogs would probably detect Bd more ef?ciently than monitoring Dixie Valley toads alone. Given that no Bd was detected, minimum detectable prevalence of Bd was <3% in 2011–2014, and <5% (Dixie Valley toads only) and <10% (American bullfrogs only) in 2019–2021. Optimal management for Bd depends on the mechanisms underlying its apparent absence from the range of Dixie Valley toads, but a balanced surveillance scheme that includes sampling American bullfrogs to increase the likelihood of detecting Bd, and adult Dixie Valley toads to ensure broad spatial coverage where American bullfrogs do not occur, would probably result in ef?cient surveillance, which might permit timely management of Bd if it is detected.
Papers & Reports Abiotic and biotic factors reduce the viability of a high-elevation salamander in its native range
Authors: Evan HC Grant; Graziella V DiRenzo; Adrianne B Brand
Date: 2023-05-20 | Outlet: Journal of Applied Ecology
1. Amphibian populations are undergoing worldwide declines, and high-elevation, range-restricted amphibian species may be particularly vulnerable to environmental stressors. In particular, future climate change may have disproportional impacts to these ecosystems. Evaluating the combined effects of abiotic changes and biotic interactions simultaneously is important for forecasting the range of future outcomes. This information is necessary to aid conservation decision-making.
2. We use field data to estimate population demographic parameters for an exemplary high-elevation amphibian species, the federally endangered Shenandoah salamander (Plethodon shenandoah). These parameters were entered into a Markov projection model which we used to forecast the future population status of the Shenandoah salamander.
3. We found that if the population maintains its current site colonization and persistence rates, it is at risk of extinction that could be exacerbated by both climate and interspecific competition.
4. Synthesis and applications. Managers have a fundamental objective directed by official policy of maintaining the species ‘for the foreseeable future (Grant et al., 2014).’ Our evaluation of multiple hypotheses about population drivers reveals that extinction is projected for this species. Our analysis suggests that considering active management need not depend on resolving the uncertainty.
2. We use field data to estimate population demographic parameters for an exemplary high-elevation amphibian species, the federally endangered Shenandoah salamander (Plethodon shenandoah). These parameters were entered into a Markov projection model which we used to forecast the future population status of the Shenandoah salamander.
3. We found that if the population maintains its current site colonization and persistence rates, it is at risk of extinction that could be exacerbated by both climate and interspecific competition.
4. Synthesis and applications. Managers have a fundamental objective directed by official policy of maintaining the species ‘for the foreseeable future (Grant et al., 2014).’ Our evaluation of multiple hypotheses about population drivers reveals that extinction is projected for this species. Our analysis suggests that considering active management need not depend on resolving the uncertainty.
Papers & Reports Complex life histories alter patterns of mercury exposure and accumulation in linked aquatic-terrestrial food webs: an amphibian example
Authors: Freya Rowland; Erin Muths; Collin A Eagles-Smith; craig stricker; Johanna M Kraus; Rachel Harrington; David M Walters
Date: 2022-12-31 | Outlet: Environmental Science and Technology
Quantifying how contaminants change across life cycles of species who undergo metamorphosis is critical to assessing risk to organisms and their consumers. Pond-breeding amphibians can dominate aquatic animal biomass as larvae and are terrestrial prey as metamorphs and adults. Thus, amphibians can be vectors of mercury accumulation in both aquatic and terrestrial food webs. However, it is still unclear how mercury concentrations are affected by exogenous (e.g., habitat or diet) vs. endogenous factors (e.g., catabolism during hibernation) as amphibians undergo large diet shifts and periods of fasting during ontogeny. We measured total mercury (THg), methylmercury (MeHg), and isotopic compositions (?13C, ?15N) in boreal chorus frogs (Pseudacris maculata) across five life stages in two metapopulations in Colorado, USA. We found large differences in MeHg concentrations and percent of THg as MeHg among life stages. Frog MeHg concentrations spiked after metamorphosis and hibernation coinciding with the most energetically demanding stages of their life cycle. Transitions among life stages led to large step changes in mercury concentrations – the endogenous processes of metamorphosis and hibernation biomagnified MeHg, decoupling isotopic compositions and MeHg concentrations. These step changes are not often considered in conventional expectations of how food web processes predict trophic transfer, accumulation, and transport of contaminants. ?
Papers & Reports Disentangling direct and indirect effects of extreme events on coastal wetland communities
Authors: Courtney L Davis; Susan C Walls; William J Barichivich; Mary E Brown; David AW Miller
Date: 2022-12-16 | Outlet: Journal of Animal Ecology
1. One of the primary ways in which climate change will impact coastal freshwater wetlands is through changes in the frequency, intensity, timing, and distribution of extreme weather events. Disentangling the direct and indirect mechanisms of population- and community-level responses to extreme events is vital to predicting how species composition of coastal wetlands will change under future conditions.
2. We extended static structural equation modeling approaches to incorporate system dynamics in a multi-year multispecies occupancy model to quantify the effects of extreme weather events on a coastal freshwater wetland system.
3. We used data from an 8-year study (2009 to 2016) on St. Marks National Wildlife Refuge in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with two flooding events in 2012 and 2013. We examine how physical changes to the landscape, including potential changes in salinity and increased wetland connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of isolated coastal wetlands.
4. We provide evidence that the primary effects of flooding on the amphibian community were through indirect mechanisms via changes in the composition of the sympatric fish community that may have had lethal (i.e., through direct predation) or non-lethal (i.e., through direct or indirect competitive interactions) effects. In addition, we shown that amphibian species differed in their sensitivity to direct flooding effects and indirect changes in the fish community and wetland specific conductance, which led to variable responses across the community. These effects led to the overall decline in amphibian species richness from 2009 to 2016, suggesting that wetland-breeding amphibian communities on St. Marks may not be resilient to predicted changes in coastal disturbance regimes as a result of climate change.
5. Understanding both direct and indirect effects, as well as species interactions, is important for predicting the effects of a changing climate on individual species, communities, and ecosystems.
2. We extended static structural equation modeling approaches to incorporate system dynamics in a multi-year multispecies occupancy model to quantify the effects of extreme weather events on a coastal freshwater wetland system.
3. We used data from an 8-year study (2009 to 2016) on St. Marks National Wildlife Refuge in Florida, USA, to quantify species-specific and community-level changes in amphibian and fish occupancy associated with two flooding events in 2012 and 2013. We examine how physical changes to the landscape, including potential changes in salinity and increased wetland connectivity, may have contributed to or exacerbated the effects of these extreme weather events on the biota of isolated coastal wetlands.
4. We provide evidence that the primary effects of flooding on the amphibian community were through indirect mechanisms via changes in the composition of the sympatric fish community that may have had lethal (i.e., through direct predation) or non-lethal (i.e., through direct or indirect competitive interactions) effects. In addition, we shown that amphibian species differed in their sensitivity to direct flooding effects and indirect changes in the fish community and wetland specific conductance, which led to variable responses across the community. These effects led to the overall decline in amphibian species richness from 2009 to 2016, suggesting that wetland-breeding amphibian communities on St. Marks may not be resilient to predicted changes in coastal disturbance regimes as a result of climate change.
5. Understanding both direct and indirect effects, as well as species interactions, is important for predicting the effects of a changing climate on individual species, communities, and ecosystems.
Papers & Reports Compensatory recruitment unlikely in high elevation amphibian populations challenged with disease
Authors: Bennett Hardy; Erin Muths; Brad A Lambert; S C Schneider; W C Funk; Larissa L Bailey
Date: 2022-07-12 | Outlet: Journal of Applied Ecology
1. Understanding the causes of population variation in host response to disease, and the mechanisms of persistence, can serve as vital information for species conservation. One such mechanism of population persistence that has gained support is the demographic process of compensatory recruitment. Host populations may persist by increasing recruitment to compensate for reduced survival due to infection, thus limiting the negative effects of the disease on population trajectories. However, high elevation populations are inherently vulnerable to stochastic processes and may be limited in their ability to exhibit compensatory recruitment relative to lower elevation populations.
2. We use long-term mark-recapture data from five populations of boreal toads (Anaxyrus boreas boreas ), across an elevational gradient in Colorado, before and after pathogen arrival to assess whether populations can persist with Batrachochytrium dendrobatidis (Bd) via compensatory recruitment.
3. Prior to pathogen arrival, we found a life history tradeoff between survival and recruitment across elevations, where high elevation toads have high survival but lower recruitment and vice versa at lower elevations.
4. Pathogen arrival had a strong negative effect on apparent annual survival and recruitment leading to negative population growth rates and dramatically reduced host abundances. The data did not support the occurrence of compensatory recruitment.
5. Synthesis and applications. Our unique dataset indicates that demographic responses to pathogens may be environmentally (i.e., elevationally) context-dependent and highlights the value of long-term monitoring. We recommend that practitioners verify that potential persistence mechanisms occur across multiple populations and relevant environmental gradients to counter any assumptions of the mechanism existing species-wide. Quantifying variation in population responses to disease will aid in understanding the bounds of such persistence mechanisms and identify particularly vulnerable populations where mechanisms are non-existent.
2. We use long-term mark-recapture data from five populations of boreal toads (Anaxyrus boreas boreas ), across an elevational gradient in Colorado, before and after pathogen arrival to assess whether populations can persist with Batrachochytrium dendrobatidis (Bd) via compensatory recruitment.
3. Prior to pathogen arrival, we found a life history tradeoff between survival and recruitment across elevations, where high elevation toads have high survival but lower recruitment and vice versa at lower elevations.
4. Pathogen arrival had a strong negative effect on apparent annual survival and recruitment leading to negative population growth rates and dramatically reduced host abundances. The data did not support the occurrence of compensatory recruitment.
5. Synthesis and applications. Our unique dataset indicates that demographic responses to pathogens may be environmentally (i.e., elevationally) context-dependent and highlights the value of long-term monitoring. We recommend that practitioners verify that potential persistence mechanisms occur across multiple populations and relevant environmental gradients to counter any assumptions of the mechanism existing species-wide. Quantifying variation in population responses to disease will aid in understanding the bounds of such persistence mechanisms and identify particularly vulnerable populations where mechanisms are non-existent.
Papers & Reports Captivity, reintroductions, and the rewilding of the amphibian microbiome
Authors: Timothy Korpita; Erin Muths; Mary K Watry; Valerie J McKenzie
Date: 2023 | Outlet: Microbial Ecology
Many studies have noted apparent differences in microbes associated with animals reared in captivity compared to their wild counterparts. Few studies have examined how microbes change when animals are reintroduced to the wild after being reared in captivity. As captive assurance populations and reintroduction programs increase, a better understanding of how microbial symbionts respond during animal translocations is critical. We examined changes in microbes of boreal toads (Anaxyrus boreas) after reintroduction to the wild following captive rearing. Boreal toads, a long-lived high elevation species, are endangered in Colorado primarily due to chytridiomycosis. Previous studies demonstrate that developmental life stage of boreal toads is an important factor in their microbiomes such that microbiomes change over the course of development. i) comparisons of the skin, mouth, and gut bacteria of boreal toads across four developmental life stages in captivity and the wild, ii) pre-metamorphic tadpole skin bacteria before and after reintroduction to the wild, and iii) adult skin bacteria during reintroduction to the wild. We used barcoded amplicon sequencing of the 16S small subunit of the rRNA gene on the Illumina MiSeq platform to characterize the bacterial communities. We demonstrated that differences occur across the skin gut and mouth microbes in captive versus wild boreal toads, and that the degree of difference depend on developmental stage. Skin bacteria from captive versus wild tadpoles were more similar relative to post-metamorphic life stages. When captive reared tadpoles were introduced to a wild site, their skin bacteria changed to mirror wild boreal toads within weeks. Similarly, the microbiome of reintroduced adult boreal toads also shifted to mirror wild-type microbes. Our results indicate that the microbial signature of boreal toads reared in captivity does not persist after release into natural habitat. The relationship between changing microbes and host health is not well understood for the majority of animal species but is an important part of wildlife conservation.
Papers & Reports Revisiting conservation units for the endangered mountain yellow-legged frog species complex (Rana muscosa, Rana sierrae) using multiple genomic methods
Authors: Allison Q Byrne; Andrew P Rothstein; Lydia L Smith; Hannah Kania; Roland A Knapp; Danial M Boiano; Cheryl J Briggs; Adam R Backlin; Robert N Fisher; Erica B Rosenblum
Date: 2023-09-29 | Outlet: Conservation Genetics https://doi.org/10.1007/s10592-023-01568-5
Insights from conservation genomics have dramatically improved recovery plans for numerous endangered species. However, most taxa have yet to benefit from the full application of genomic technologies. The mountain yellow-legged frog species complex, Rana muscosa and Rana sierrae, inhabits the Sierra Nevada mountains and Transverse/Peninsular Ranges of California and Nevada. Both species have declined precipitously throughout their historical distributions. Conservation management plans outline extensive ongoing recovery efforts but are still based on the genetic structure determined primarily using a single mitochondrial sequence. Our study used two different sequencing strategies – amplicon sequencing and exome capture – to refine our understanding of the population genetics of these imperiled amphibians. We used buccal swabs, museum tissue samples, and archived skin swabs to genotype frog populations across their range. Using the amplicon sequencing and exome capture datasets separately and combined, we document five major genetic clusters. Notably, we found evidence supporting previous species boundaries within Kings Canyon National Park with some exceptions at individual sites. Though we see evidence of genetic clustering, especially in the R. muscosa clade, we also found evidence of some admixture across cluster boundaries in the R. sierrae clade, suggesting a stepping-stone model of population structure. We also find that the southern R. muscosa cluster had large runs of homozygosity and the lowest overall heterozygosity of any of the clusters, consistent with previous reports of marked declines in this area. Overall, our results clarify management unit designations across the range of an endangered species and highlight the importance of sampling the entire range of a species, even when collecting genome-scale data.
Papers & Reports Winter severity affects occupancy of spring- and summer-breeding anurans across the eastern United States
Authors: Sara R weiskopf; Alexey N Shiklomanov; Laura Thompson; Sarah Wheedleton; Evan HC Grant
Date: 2022-08-09 | Outlet: Diversity and Distributions
Climate change is an increasingly important driver of biodiversity loss. The ectothermic nature of amphibians may make them particularly sensitive to changes in normal temperature and precipitation regimes, exacerbating global declines from other threats. In this study, we used large-scale citizen science data from the eastern half of the United States to assess how variation in winter severity influenced occupancy dynamics of 11 anuran species. We found that most species had increased occupancy in years with greater than average snow cover and warmer than average mean winter temperatures. Surprisingly, we found that climatic conditions in winter affected occupancy dynamics of both spring and summer breeding species, indicating that changing winter conditions may have consequences for anuran species with varying life history characteristics. As the climate continues to change, expected reductions in snowpack may act as an additional stressor on already declining anuran populations, while milder winters may improve overwinter survival for some species.
Papers & Reports Cryptic declines of small, cold-water specialists highlight potential vulnerabilities of headwater streams as climate refugia
Authors: Blake R Hossack; M LeMoine; Emily B Oja; Lisa A Eby
Date: 2023 | Outlet: Biological Conservation
Increasing temperatures and climate-driven disturbances like wildfire are a growing threat to many species,
including cold-water specialists. Montane areas and cold streams are often considered climate refugia that buffer
communities against change. However, climate refugia are often species-specific, and despite growing awareness
that life histories and habitat requirements shape responses to change, small or non-game species are often
under-represented in monitoring and planning programs. A recent study in Montana, USA, revealed much larger
warming-related declines in occupancy for small, non-game slimy sculpin (Cottus cognatus) between 1993 and
1995 and 2011–2013 than for two socially valued salmonid fishes that shape regional conservation efforts. To
broaden insight into climate change vulnerabilities of headwater stream communities, we analyzed data for
Rocky Mountain tailed frogs (Ascaphus montanus) that were collected during those same electrofishing surveys
for fishes from 241 stream reaches. Tailed frogs occupy small, cold streams and have several life-history traits
that make them sensitive to environmental change. We used a Bayesian framework to estimate occupancy,
colonization, and extinction dynamics relative to forest canopy, estimated stream temperature, and wildfire
effects. Tailed frog occupancy decreased by 19 % from 1993 to 1995 to 2011–2013. Changes in occupancy were
linked with increased extinction and reduced colonization where there were fire-driven reductions in canopy
cover, and reduced colonization of stream reaches that warmed on average 0.8 ?C during the study. Our results
highlight extensive extirpations for oft-overlooked species and emphasize the importance of including species
with diverse habitat requirements and life histories in conservation planning.
including cold-water specialists. Montane areas and cold streams are often considered climate refugia that buffer
communities against change. However, climate refugia are often species-specific, and despite growing awareness
that life histories and habitat requirements shape responses to change, small or non-game species are often
under-represented in monitoring and planning programs. A recent study in Montana, USA, revealed much larger
warming-related declines in occupancy for small, non-game slimy sculpin (Cottus cognatus) between 1993 and
1995 and 2011–2013 than for two socially valued salmonid fishes that shape regional conservation efforts. To
broaden insight into climate change vulnerabilities of headwater stream communities, we analyzed data for
Rocky Mountain tailed frogs (Ascaphus montanus) that were collected during those same electrofishing surveys
for fishes from 241 stream reaches. Tailed frogs occupy small, cold streams and have several life-history traits
that make them sensitive to environmental change. We used a Bayesian framework to estimate occupancy,
colonization, and extinction dynamics relative to forest canopy, estimated stream temperature, and wildfire
effects. Tailed frog occupancy decreased by 19 % from 1993 to 1995 to 2011–2013. Changes in occupancy were
linked with increased extinction and reduced colonization where there were fire-driven reductions in canopy
cover, and reduced colonization of stream reaches that warmed on average 0.8 ?C during the study. Our results
highlight extensive extirpations for oft-overlooked species and emphasize the importance of including species
with diverse habitat requirements and life histories in conservation planning.
Papers & Reports Empirical evidence for effects of invasive American Bullfrogs on occurrence of native amphibians and emerging pathogens
Authors: Blake R Hossack; Emily B Oja; Audrey Owens; D Hall; C L Crawford; Caren S Goldberg; S Hedwall; J A Lemos-Espinal; S MacVean; Magnus McCaffery; Erin Muths; A McCall; C Mosley; Brent H Sigafus; M J Sredl,; James C Rorabaugh
Date: 2023 | Outlet: Ecological Applications
Invasive species and emerging infectious diseases are two of the greatest
threats to biodiversity. American Bullfrogs (Rana [Lithobates] catesbeiana),
which have been introduced to many parts of the world, are often linked with
declines in native amphibians via predation and the spread of emerging pathogens
such as amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd])
and ranaviruses. Although many studies have investigated the potential role of
bullfrogs in the decline of native amphibians, analyses that account for shared
habitat affinities and imperfect detection have found limited support for
clear effects. Similarly, the role of bullfrogs in shaping the patch-level distribution
of pathogens is unclear. We used eDNA methods to sample 233 sites in the southwestern USA and Sonora, Mexico (2016–2018) to estimate how
the presence of bullfrogs affects the occurrence of four native amphibians,
Bd, and ranaviruses. Based on two-species, dominant-subordinate occupancy
models fitted in a Bayesian context, federally threatened Chiricahua Leopard
Frogs (Rana chiricahuensis) and Western Tiger Salamanders (Ambystoma
mavortium) were eight times (32% vs. 4%) and two times (36% vs. 18%), respectively,
less likely to occur at sites where bullfrogs occurred. Evidence for the
negative effects of bullfrogs on Lowland Leopard Frogs (Rana yavapaiensis)
and Northern Leopard Frogs (Rana pipiens) was less clear, possibly because of
smaller numbers of sites where these native species still occurred and because
bullfrogs often occur at lower densities in streams, the primary habitat for
Lowland Leopard Frogs. At the community level, Bd was most likely to occur
where bullfrogs co-occurred with native amphibians, which could increase the
risk to native species. Ranaviruses were estimated to occur at 33% of bullfrogonly
sites, 10% of sites where bullfrogs and native amphibians co-occurred,
and only 3% of sites where only native amphibians occurred. Of the 85 sites
where we did not detect any of the five target amphibian species, we also did
not detect Bd or ranaviruses; this suggests other hosts do not drive the distribution
of these pathogens in our study area. Our results provide landscape-scale
evidence that bullfrogs reduce the occurrence of native amphibians and
increase the occurrence of pathogens, information that can clarify risks and
aid the prioritization of conservation actions.
threats to biodiversity. American Bullfrogs (Rana [Lithobates] catesbeiana),
which have been introduced to many parts of the world, are often linked with
declines in native amphibians via predation and the spread of emerging pathogens
such as amphibian chytrid fungus (Batrachochytrium dendrobatidis [Bd])
and ranaviruses. Although many studies have investigated the potential role of
bullfrogs in the decline of native amphibians, analyses that account for shared
habitat affinities and imperfect detection have found limited support for
clear effects. Similarly, the role of bullfrogs in shaping the patch-level distribution
of pathogens is unclear. We used eDNA methods to sample 233 sites in the southwestern USA and Sonora, Mexico (2016–2018) to estimate how
the presence of bullfrogs affects the occurrence of four native amphibians,
Bd, and ranaviruses. Based on two-species, dominant-subordinate occupancy
models fitted in a Bayesian context, federally threatened Chiricahua Leopard
Frogs (Rana chiricahuensis) and Western Tiger Salamanders (Ambystoma
mavortium) were eight times (32% vs. 4%) and two times (36% vs. 18%), respectively,
less likely to occur at sites where bullfrogs occurred. Evidence for the
negative effects of bullfrogs on Lowland Leopard Frogs (Rana yavapaiensis)
and Northern Leopard Frogs (Rana pipiens) was less clear, possibly because of
smaller numbers of sites where these native species still occurred and because
bullfrogs often occur at lower densities in streams, the primary habitat for
Lowland Leopard Frogs. At the community level, Bd was most likely to occur
where bullfrogs co-occurred with native amphibians, which could increase the
risk to native species. Ranaviruses were estimated to occur at 33% of bullfrogonly
sites, 10% of sites where bullfrogs and native amphibians co-occurred,
and only 3% of sites where only native amphibians occurred. Of the 85 sites
where we did not detect any of the five target amphibian species, we also did
not detect Bd or ranaviruses; this suggests other hosts do not drive the distribution
of these pathogens in our study area. Our results provide landscape-scale
evidence that bullfrogs reduce the occurrence of native amphibians and
increase the occurrence of pathogens, information that can clarify risks and
aid the prioritization of conservation actions.
Papers & Reports Future changes in habitat availability for two specialist snake species in the imperiled rocklands of South Florida, U.S.A
Authors: Suresh C. Subedi; Susan C Walls; William J Barichivich; Ryan Boyles; Michael S. Ross; J Aa Hogan; John A Tupy
Date: 2022-08-30 | Outlet: Conservation Science and Practice
Rockland habitat in South Florida, USA, is a threatened ecosystem that has been lost, fragmented, or degraded because of urbanization or other anthropogenic disturbance. Furthermore, low-lying islands and coastal areas are experiencing sea-level rise (SLR) and an increased frequency and intensity of tidal flooding, putting rockland habitats there at increasing risk of ecological change. We evaluated changes in the extent of rockland habitat under various scenarios of future SLR, tidal flooding, and human development for two endemic state-listed threatened species of snakes, the Rim Rock Crowned Snake (Tantilla oolitica) and the Key Ring-necked Snake (Diadophis punctatus acricus). Both snakes are restricted to South Florida. We used recent and historical species’ records to determine each species’ habitat range. We then estimated the extent of future habitat loss due to SLR and continued human development, as well as degradation of the remaining habitat. We also asked whether the future potential drivers of habitat loss and degradation differ between the two species and across their habitat ranges. We predicted that saltwater intrusion could negatively affect rocklands by 2050, resulting in degradation of 80% of the existing habitat because of an anticipated 42 cm of SLR. Moreover, short-term stochastic events such as storm surge and high tides will increasingly saturate the root zone of rockland vegetation before complete inundation. Most of the rockland habitat used by these two species of snakes will be inundated by 2080. Sea level rise will likely change current rocklands into more halophytic habitat (mangrove or salt marsh wetland) within 50 to 60 years. As much as 47% of rockland habitat will be lost due to human development by 2030. Therefore, immediate mitigation actions may be needed to conserve specialist species within rockland habitat that is threatened by human activities and climate change.
Papers & Reports Hot, wet, and rare: modeling the occupancy dynamics of the narrowly distributed Dixie Valley Toad
Authors: Jonathan P Rose; Patrick M Kleeman; Brian J Halstead
Date: 2022-08-29 | Outlet: Wildlife Research
Small population sizes and no possibility of metapopulation rescue put narrowly distributed endemic species under elevated risk of extinction from anthropogenic change. Desert spring wetlands host many endemic species that require aquatic habitat and are isolated by the surrounding xeric terrestrial habitat. Aims. We sought to model the occupancy dynamics of the Dixie Valley toad (Anaxyrus williamsi), a recently described species endemic to a small desert spring wetland complex in Nevada, USA. Methods. We divided the species’ range into 20 m × 20 m cells and surveyed for Dixie Valley toads at 60 cells during six primary periods from 2018 to 2021, following an occupancy study design. We analysed our survey data by using a multi-state dynamic occupancy model to estimate the probability of adult occurrence, colonisation, site survival, and larval occurrence and the relationship of each to environmental covariates. Key results. The detection probabilities of adult and larval toads were affected by survey length and time of day. Adult Dixie Valley toads were widely distributed, with detections in 75% of surveyed cells at some point during the 3-year study, whereas larvae were observed only in 20% of cells during the study. Dixie Valley toad larvae were more likely to occur in cells far from spring heads with a high coverage of surface water, low emergent vegetation cover, and water temperatures between 20°C and 28°C. Adult toads were more likely to occur in cells with a greater coverage of surface water and water depth >10 cm. Cells with more emergent vegetation cover and surface water were more likely to be colonised by adult toads. Conclusions. Our results showed that Dixie Valley toads are highly dependent on surface water in both spring and autumn. Adults and larvae require different environmental conditions, with larvae occurring farther from spring heads and in fewer cells. Implications. Disturbances to the hydrology of the desert spring wetlands in Dixie Valley could threaten the persistence of this narrowly distributed toad.
Papers & Reports Invasive bullfrogs maintain MHC polymorphism including alleles associated with chytrid fungal infection
Authors: Jacob LaFond; Katherine R Martin; Hollis Dahn; Jonathan Q Richmond; Robert W Murphy; Njal Rollinson; Anna E Savage
Date: 2022-05-19 | Outlet: Integrative and Comparative Biology 62:262–274
Maintenance of genetic diversity at adaptive loci may facilitate invasions by non-native species by allowing populations to adapt to novel environments, despite the loss of diversity at neutral loci that typically occurs during founder events. To evaluate this prediction, we compared genetic diversity at major histocompatibility complex (MHC) and cytochrome b (cytb) loci from 20 populations of the American bullfrog (Rana catesbeiana) across the invasive and native ranges in North America and quantified the presence of the pathogen Batrachochytrium dendrobatidis (Bd). Compared to native populations, invasive populations had significantly higher Bd prevalence and intensity, significantly higher pairwise MHC and cytb FST, and significantly lower cytb diversity, but maintained similar levels of MHC diversity. The two most common MHC alleles (LiCA_B and Rapi_33) were associated with a significant decreased risk of Bd infection, and we detected positive selection acting on four peptide binding residues. Phylogenetic analysis suggested invasive populations likely arose from a single founding population in the American Midwest with a possible subsequent invasion in the northwest. Overall, our study suggests that the maintenance of diversity at adaptive loci may contribute to invasion success and highlights the importance of quantifying diversity at functional loci to assess the evolutionary potential of invasive populations.
Papers & Reports Biofluorescence in tiger salamanders documented in Rocky Mountain National Park for the first time
Authors: Benjamin Lafrance; Andrew M Ray; Amanda M Kissel; Erin Muths
Date: 2021-12 | Outlet: Park Science
Recent work has shown that many amphibians are biofluorescent. Biofluorescence describes an organism’s ability to absorb visible and ultraviolet light and re-emit it at a lower energy level (e.g., blue light re-emitted as green fluorescence). However, the function of fluorescence in amphibians is unclear. We observed paedomorphic western tiger salamanders at Lily Lake in Rocky Mountain National Park and obtained the first images recorded at this park of biofluorescence in these animals in response to blue light.
Papers & Reports Using physiological conditions to assess current and future habitat use of a Subarctic frog
Authors: Thomas P Hastings; Blake R Hossack; L Fishback; J M Davenport
Date: 2022 | Outlet: Integrative Zoology
Species with especially close dependence on the environment to meet physiological requirements, such as ectotherms, are highly susceptible to the impacts of climate change. Climate change is occurring rapidly in the Subarctic and Arctic, but there is limited knowledge on ectotherm physiology in these landscapes. We investigated how environmental conditions and habitat characteristics influence the physiological conditions and habitat use of wood frogs (Rana sylvatica, LeConte 1825) in a Subarctic landscape near Churchill, Manitoba (Canada). We used plaster models to estimate water loss rates and surface body temperatures among different habitat types and at specific locations used by radio-tracked frogs. Water loss (R^2 = 0.67) and surface temperature (R^2 = 0.80) of plaster models was similar to that of live frogs. Model-based water loss rates were greater in tundra habitat than in boreal forest and ecotone habitat. Habitat use of wood frogs was strongly tied with available surface moisture and decreased water loss rates that were observed with plaster models. Environmental conditions, such as wind speed and ground temperature, explained 58% and 91% of the variation in water balance and temperature of plaster models. Maintaining physiological conditions may be challenging for semi-aquatic ectotherms in environments vulnerable to future climate change. The ability to predict physiological conditions based on environmental conditions, as demonstrated in our study, can help understand how wildlife will respond to climatic changes.