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Papers & Reports Resilience of native amphibian communities following catastrophic drought: evidence from a decade of regional-scale monitoring
Authors: W Moss; T McDevitt-Galles; Erin Muths; Steven Bobzien; J Purificato; P TJ Johnson
1. The increasing frequency and severity of drought has the potential to exacerbate existing global amphibian declines. However, interactions between drought and coincident stressors, coupled with high interannual variability in amphibian abundances, can mask the extent and underlying mechanisms of drought-induced declines. The application of dynamic occupancy modeling to longitudinal monitoring data estimates the effect of specific variables on population change, providing key insights into potential management strategies for drought resilience.
2. We synthesized a decade (2009 – 2019) of amphibian survey data from multiple monitoring programs across the California Bay Area and used occupancy modeling to estimate the influence of drought, invasive species, and land use on species’ persistence and colonization probabilities. The geographic and temporal scale of our dataset, consisting of 2574 surveys of seven species in 473 ponds, allowed us to quantify regional trends for an entire community of pond-breeding amphibians.
3. An extreme drought from 2012 – 2015 resulted in losses of breeding sites, with 51% of ponds drying in 2014 compared to <10% in non-drought years. Pond drying reduced persistence rates, and nearly every species exhibited reduced occupancy during the drought, with some species (American bullfrogs and California newts) declining by > 25%. Drought reduced occupancy via additional mechanisms beyond habitat loss; for example, lower spring precipitation (an important cue for breeding) was associated with reduced colonization.
4. During drought, native species’ persistence was higher in permanent relative to temporary ponds, even though these sites were also more likely to contain invasive fish and bullfrogs, which generally reduced native amphibian occupancy. Many of these permanent ponds dried during the worst year of drought, leading to extirpations of invasive species that appeared long-lasting. In contrast, native species rebounded quickly with returning rains and showed evidence of full recovery.
5. Synthesis and applications: Despite experiencing one of most severe droughts in a millennium, native species displayed high resilience. Due to longer recovery times by non-native relative to native species, drought presents a valuable management opportunity to remove invaders from key refugia, and we highlight the value of maintaining hydroperiod diversity to promote the persistence of multiple species.
2. We synthesized a decade (2009 – 2019) of amphibian survey data from multiple monitoring programs across the California Bay Area and used occupancy modeling to estimate the influence of drought, invasive species, and land use on species’ persistence and colonization probabilities. The geographic and temporal scale of our dataset, consisting of 2574 surveys of seven species in 473 ponds, allowed us to quantify regional trends for an entire community of pond-breeding amphibians.
3. An extreme drought from 2012 – 2015 resulted in losses of breeding sites, with 51% of ponds drying in 2014 compared to <10% in non-drought years. Pond drying reduced persistence rates, and nearly every species exhibited reduced occupancy during the drought, with some species (American bullfrogs and California newts) declining by > 25%. Drought reduced occupancy via additional mechanisms beyond habitat loss; for example, lower spring precipitation (an important cue for breeding) was associated with reduced colonization.
4. During drought, native species’ persistence was higher in permanent relative to temporary ponds, even though these sites were also more likely to contain invasive fish and bullfrogs, which generally reduced native amphibian occupancy. Many of these permanent ponds dried during the worst year of drought, leading to extirpations of invasive species that appeared long-lasting. In contrast, native species rebounded quickly with returning rains and showed evidence of full recovery.
5. Synthesis and applications: Despite experiencing one of most severe droughts in a millennium, native species displayed high resilience. Due to longer recovery times by non-native relative to native species, drought presents a valuable management opportunity to remove invaders from key refugia, and we highlight the value of maintaining hydroperiod diversity to promote the persistence of multiple species.
Papers & Reports Staggered-entry analysis of breeding and occupancy dynamics of Arizona Toads from historically occupied habitats of New Mexico, USA
Authors: M J Forzley; Mason J Ryan; I M Latella; J T Giermakowski; Erin Muths; Brent H Sigafus; Blake R Hossack
Date: 2021 | Outlet: Ichthyology & Herpetology
For species with variable phenology, it is often challenging to produce reliable estimates of population dynamics or changes in occupancy. The Arizona Toad (Anaxyrus microscaphus) is a southwestern USA endemic that has been petitioned for legal protection, but status assessments are limited by a lack of information on population trends. Also, timing and consistency of Arizona Toad breeding varies greatly, making it difficult to predict optimal survey times or effort required for detection. To help fill these information gaps, we conducted breeding season call surveys during 2013–2016 and 2019 at 86 historically occupied sites and 59 control sites across the species’ range in New Mexico. We estimated variation in mean dates of arrival and departure from breeding sites, changes in occupancy, and site-level extinction since 1959 with recently developed multi-season staggered-entry models, which relax the within-season closure assumption common to most occupancy models. Optimal timing of surveys in our study areas was approximately March 5 - March 30. Averaged across years, estimated probability of occupancy was https://0.58 (SE = 0.09) for historical sites and https://0.19 (SE = 0.08) for control sites. Occupancy increased from 2013 through 2019. Notably, even though observer error was trivial, annual detection probabilities varied from https://0.23 to https://0.75 and declined during the study; this means naïve occupancy values would have been misleading, indicating apparent declines in toad occupancy. Occupancy was lowest during the first year of the study, possibly due to changes in stream flows and conditions in many waterbodies following extended drought and recent wildfires. Although within-season closure was violated by variable calling phenology, simple multi-season models provided nearly identical estimates as staggered-entry models. Surprisingly, extinction probability was unrelated to the number of years since the first or last record at historically occupied sites. Collectively, our results suggest a lack of large, recent declines in occupancy by Arizona Toads in New Mexico, but we still lack population information from most of the species’ range.
Papers & Reports Thermal conditions predict intraspecific variation in senescence rate in frogs and toads
Authors: Hugo Cayuela; Rebecca M McCaffery; Thierry Frétey; Benedikt R Schmidt; Kurt Grossenbacher; Omar Lenzi; Blake R Hossack; Brad A Lambert; Johan Elmberg; J Merilä; J Gippet; David S Pilliod; Erin Muths
Date: 2021-11 | Outlet: PNAS
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 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, Rana temporaria) and Bufonidae (Anaxyrus boreas, 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 increase predicted by IPCC 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.
Papers & Reports Sex-related differences in aging rate are associated with sex chromosome system in amphibians
Authors: Hugo Cayuela; J Lemaître; Jean-Paul Lena; Victor Ronget; Iñigo Martinez-Solano; Erin Muths; David S Pilliod; Jean-Francois Lemaitre
Date: 2021-12 | Outlet: Evolution
Sex-related differences in mortality are widespread in the living world. Although sexual selection and environmental conditions might drive sex-specific variation in lifespan, recent findings suggest that sex chromosome systems are also involved. However, the influence of sex chromosome systems on aging rate (i.e., the rate of increase of mortality with age), a mortality metric that only partially correlates with lifespan, has not been investigated so far, due to an apparent lack of demographic data from clades including both XY (with heterogametic males) and ZW (with heterogametic females) sex-determination systems. Taking advantage of a unique collection of capture-recapture datasets in amphibians, a vertebrate group where XY and ZW systems have repeatedly switched over the past 200 million years we examine whether sex heterogamety can predict sex-differences in aging rates. We show that variation in aging rate only accounts for a moderate proportion of the variation in lifespan, similarly to what has been reported in mammals. Moreover, our results demonstrate that the system of genetic sex-determination has a critical impact on aging rate in clades that include closely related taxa with XY vs. ZW systems. In both systems the heterogametic sex experiences a higher aging rate compared to the homogametic sex. This new finding suggests that exposed recessive deleterious mutations on the X/Z chromosome (the “unguarded X/Z effect”) or repeat-rich Y/W chromosome (the “toxic Y/W effect”) could accelerate aging in the heterogametic sex.
Papers & Reports Why disease ecology needs life-history theory: a host perspective
Authors: Andrés Valenzuela-Sánchez; M Wilbur; Stefano Canessa; Leonardo Bacigalupe; Erin Muths; Benedikt R Schmidt; A C Cunningham; A Ozgul; P TJ Johnson; Hugo Cayuela
Date: 2020-12 | Outlet: Ecology Letters
When facing an emerging infectious disease of conservation concern, we often have little
information on the nature of the host-parasite interaction to inform management decisions.
However, it is becoming increasingly clear that the life-history strategies of host species
can be predictive of individual- and population-level responses to infectious disease, even
without detailed knowledge on the specifics of the host-parasite interaction. Here, we argue
that a deeper integration of life-history theory into disease ecology is timely and necessary
to improve our capacity to understand, predict, and mitigate the impact of endemic and
emerging infectious diseases in wild populations. Using wild vertebrates as an example, we
show that host life-history characteristics influence host responses to parasitism at different
levels of organization, from individuals to communities. We also highlight knowledge gaps
and future directions for the study of life-history and host responses to parasitism. We
conclude by illustrating how this theoretical insight can inform the monitoring and control
of infectious diseases in wildlife.
information on the nature of the host-parasite interaction to inform management decisions.
However, it is becoming increasingly clear that the life-history strategies of host species
can be predictive of individual- and population-level responses to infectious disease, even
without detailed knowledge on the specifics of the host-parasite interaction. Here, we argue
that a deeper integration of life-history theory into disease ecology is timely and necessary
to improve our capacity to understand, predict, and mitigate the impact of endemic and
emerging infectious diseases in wild populations. Using wild vertebrates as an example, we
show that host life-history characteristics influence host responses to parasitism at different
levels of organization, from individuals to communities. We also highlight knowledge gaps
and future directions for the study of life-history and host responses to parasitism. We
conclude by illustrating how this theoretical insight can inform the monitoring and control
of infectious diseases in wildlife.
Papers & Reports Density dependence and adult survival drive dynamics in two high elevation amphibian populations
Authors: Amanda M Kissel; S Tenan; Erin Muths
Date: 2020-12-12 | Outlet: Diversity 2020, 12, 478; doi:10.3390/d12120478
Amphibian conservation has progressed from the identification of declines to mitigation, but efforts are hampered by the lack of nuanced information about the effects of environmental characteristics and stressors on mechanistic processes of population regulation. Challenges include a paucity of long-term data and scant information about the relative roles of extrinsic (e.g., weather) and intrinsic (e.g., density dependence) factors. We used a Bayesian formulation of an open population capture-recapture model and >30 years of data to examine intrinsic and extrinsic factors regulating two adult boreal chorus frogs (Pseudacris maculata) populations. We modelled population growth rate and apparent survival directly, assessed their temporal variability, and derived estimates of recruitment. Populations were relatively stable (geometric mean population growth rate >1), and regulated by negative density dependence (i.e., higher population sizes reduced population growth rate). In the smaller population, density dependence also acted on adult survival. In the larger population, higher population growth was associated with warmer autumns. Survival estimates ranged from https://0.30-0.87, per-capita recruitment was <1 in most years, and mean seniority probability was >https://0.50, suggesting adult survival is more important to population growth than recruitment. Our analysis indicates density dependence is a primary driver of population dynamics for P. maculata adults.
Papers & Reports Accommodating the role of site memory in dynamic species distribution models using detection/non-detection data
Authors: Graziella V DiRenzo; A David; Blake R Hossack; Brent H Sigafus; P E Howell; Evan HC Grant; Erin Muths
Outlet: Ecology xx:xxx-xxx
First-order dynamic occupancy models (FODOMs) are a class of state-space model in which the true state (occurrence) is observed imperfectly. An important assumption of FODOMs is that site dynamics only depend on the current state and that variations in dynamic processes are adequately captured with covariates or random effects. However, it is often difficult to measure the covariates that generate ecological data, which are often spatio-temporally correlated. Consequently, the non-independent error structure of correlated data causes underestimation of parameter uncertainty and poor ecological inference. Here, we extend the FODOM framework with a second-order Markov process to accommodate site memory when covariates are not available. Our modeling framework can be used to make reliable inference about site occupancy, colonization, extinction, turnover, and detection probabilities. We present a series of simulations to illustrate the data requirements and model performance. We then applied our modeling framework to 13 years of data from an amphibian community in southern Arizona, USA and find that site memory helps describe dynamic processes for most species. Our approach represents a valuable advance in obtaining inference on population dynamics, especially as they relate to metapopulations.
Data Release Data realease for manuscript: A statistical forecasting approach to metapopulation viability analysis
Authors: P E Howell; Blake R Hossack; Erin Muths; Brent H Sigafus; A Chenevert-Steffler; Richard Chandler
Date: 2020 | Outlet: Ecological Applications 2020: e02038
Data release and code for Ecological Applications paper: A statistical forecasting approach to metapopulation viability analysis
News & Stories Information from ARMI surveys guides management action in the Desert Southwest
Authors: Brent H Sigafus; Blake R Hossack; Erin Muths
September 15, 2020
The Buenos Aires National Wildlife Refuge (BANWR) has developed a new pond designed to replicate ciénega conditions that will provide habitat for the federally threatened Chiricahua leopard frog. Reintroduced to the Refuge after extirpation in the early 2000s, the Chiricahua leopard frog has colonized areas beyond the initial reintroduction sites, now inhabiting several human-made stock tanks on the Refuge. The species’ persistence on the Refuge depends on the ongoing eradication of invasive bullfrogs and the availability of water. In desert habitats such as BANWR, the ciénega (a Spanish word for wetland) is a marsh-like habitat that is critical for numerous desert-dwelling creatures. Ciénegas on BANWR are characterized by a spring or seep that saturates the soil and allows water to pool in small areas (Hendrickson and Minckley, 1985). Ciénega vegetation includes rushes, watercress, and smartweed; they are often bordered by cottonwood and willow trees which the Refuge will plant at the new ciénega once the water has settled into the excavated depression. The new ciénega on BANWR is plumbed, meaning that water levels can be modified and maintained in response to environmental conditions that range from multi-year droughts to heavy monsoon conditions (Bezy et. al. 2007).
ARMI has collected data at BANWR since 2000, gathering information about native species (e.g., Chandler et al. 2015, Jarchow et al. 2016, , Howell et al. 2018, 2020a), invasive species such as American bullfrogs and sunfish (Suhr 2010, Howell et al. 2020b), and disease (Sigafus et al. 2014). Models assessing occupancy and movement of the Chiricahua leopard frog indicate that water availability and permanency are critical components to the its persistence at BANWR. The Refuge has used this information to make decisions about management actions such as building plumbed ponds — a non-trivial action in terms of cost and logistics. The new ciénega will not only support the Chiricahua leopard frog but will provide water for many other species that call BANWR home including the federally endangered masked bobwhite quail, great blue herons, yellow-billed cuckoos, and pronghorn.
Bezy, J., C. F. Hutchinson, and C. J. Bahre. 2007. Buenos Aires National Wildlife Refuge, 373 Arizona. Desert Plants 23:3–44.
Chandler, R., E. Muths, B. H. Sigafus, C.R. Schwalbe, C. Jarchow, and B.R. Hossack. 2015. Realizing the potential of spatially explicit metapopulation theory for predicting extinction risk. Journal of Applied Ecology. DOI: 10.1111/1365-2664.12481.
Howell, P., E. Muths, B.R. Hossack, B.H. Sigafus, and R.B. Chandler. 2018. Increasing connectivity between metapopulation ecology and landscape ecology. Ecology 99: 1119-1128.
Howell, P.E., B.R. Hossack, E. Muths, B. Sigafus, A. Chenevert- Steffler, and R. Chandler. 2020a. A statistical forecasting approach to metapopulation viability analysis. Ecological Applications 30(2), e02038
Howell, P.E. E. Muths, B.H. Sigafus, and B.R. Hossack. 2020b. Survival estimates for the invasive American bullfrog. Amphibia-Reptilia.
Hendrickson, D. A. and W. L. Minckley. 1985. Ciénegas vanishing climax communities of the American southwest. Desert Plants 6 (3): 131-175.
Sigafus, B. H., C.R. Schwalbe, B.R. Hossack, and E. Muths. 2014. Prevalence of the amphibian chytrid fungus at Buenos Aires National Wildlife Refuge, Arizona. Herpetological Review 45: 41-42.
Suhre, D. O. 2010. Dispersal and demography of the American Bullfrog (Rana catesbeiana) in a 455 semi-arid grassland. M.S. Thesis, University of Arizona, USA.
Papers & Reports Determinants and consequences of dispersal in vertebrates with complex life cycles: a review of pond-breeding amphibians
Authors: Hugo Cayuela; Andrés Valenzuela-Sánchez; L Teulier; Iñigo Martinez-Solano; Jean-Paul Lena; J Merila; Erin Muths; Richard Shine; L Quay; M Denoel; Jean Clobert; Benedikt R Schmidt
Date: 2020-02 | Outlet: The Quarterly Review of Biology
Dispersal is a central process in ecology and evolution. It strongly influences the dynamics of spatially structured populations and affects evolutionary processes by shaping patterns of gene flow. For these reasons, dispersal has received considerable attention from ecologists, evolutionary biologists, and conservationists. However, although it has been studied extensively in taxa such as birds and mammals, much less is known about dispersal in vertebrates with complex life cycles such as pond-breeding amphibians. Over the past two decades researchers have taken an ever-increasing interest in amphibian dispersal and initiated both fundamental and applied studies, using a broad range of experimental and observational approaches. This body of research reveals complex dispersal patterns, causations and syndromes, with dramatic consequences for the demography, genetic, and the conservation of amphibian populations. In this review, our goals are to (1) redefine and clarify the concept of amphibian dispersal, (2) review current knowledge about the effects of individual (i.e., condition-dependent dispersal) and environmental (i.e., context-dependent dispersal) factors during the three stages of dispersal (i.e., emigration, immigration, transience), (3) identify the demographic and genetic consequences of dispersal in spatially structured amphibian populations, and (4) propose new research avenues to extend our understanding of amphibian dispersal.
Papers & Reports Hydroperiod and previous breeding success influence recruitment dynamics for a declining amphibian species
Authors: J Crockett; Erin Muths; Larissa L Bailey
Date: 2020-02 | Outlet: Population Ecology, 62(2), pp.258-268.
Populations of pond-breeding amphibians often have boom and bust patterns in recruitment, with large numbers of individuals metamorphosing in some years and few or none in other years. Environmental processes, such as pond freezing and drying, and biological factors (e.g., disease and predator community) can influence survival of early life stages and the probability of complete reproductive failure for amphibian populations. We used multi-state occupancy models to estimate probability of breeding and successful metamorphosis (the complements of reproductive failure), and explored environmental and biological factors influencing these processes.We applied both static and dynamic multistate occupancy modeling techniques to ten years (2001-2010) of boreal toad (Anaxyrus boreas boreas) data from 116 sites, and tested relationships between these probabilities and the presence of a pathogen (Batrachochytrium dendrobatidis), elevation, hydrology, relative snowpack in a given year, and the presence of trout (Onchorhyncus spp., Salvelinus fontinalis, and Salmo trutta). The probability of breeding at a site was influenced by elevation, with higher-elevation sites more likely to support breeding. The probability of metamorphosis, given breeding, was influenced by an interaction between hydrology and relative annual snowpack. The probability of metamorphosis was higher at ephemeral sites in years of relatively high snowpack, while at permanent sites, years of low snowpack lead to higher probabilities of metamorphosis. Across all sites, the probability of metamorphosis was high (0.75) for years with median snowpack levels at sites with recent breeding attempts, but lower (0.25) at newly colonized sites. Our results suggest that boreal toads are well-adapted to their current habitat, with both ephemeral and permanent sites likely to support breeding in years of median snowpack. However shifts in precipitation patterns or temperatures may have negative impacts on this species.
Data Release Amphibian Occupancy and Effects of Habitat Use on Pesticide Exposure in Iowa Wetlands
Authors: J E Swanson,; Erin Muths; Clay L Pierce; M Vandever; Kelly L Smalling
Date: 2018-03-09 | Outlet: US Geological Survey Data Release
Amphibians living in agricultural areas encounter many challenges. Two factors affecting individuals in these landscapes are habitat loss and pesticides. This thesis focuses on amphibians using agricultural wetlands in Iowa, where row crops such as corn and soybeans dominate the landscape. The goal of of the first study was to determine the influences of site characteristics on amphibian presence and success. Occupancy analysis was used to estimate proportion of area occupied by four species as a function of eight covariates hypothesized to affect occupancy: fish abundance, salamander abundance, invertebrate density, vegetative cover, wetland area, water atrazine concentration, surrounding crop land use, and overall wetland health score. We surveyed 27 wetlands in 2015 and 2016. Occupancy analysis results indicate almost all covariates were supported in our model sets although their estimated effects were weak. Direction of predicted effects of covariates on amphibians varied by species and life stage. Results show that wetland site occupancy for species in our study ranged from https://0.23 to https://0.95. Although we did not find strong evidence that the environmental factors we measured influenced amphibian occupancy, we provide insight on amphibian use of a modified agricultural landscape. The goal of the second study was to understand where and when frogs are most susceptible to pesticide exposure and how that exposure relates to accumulation. We hypothesized habitat use would influence a frog’s exposure to pesticides. We radio tracked 72 Northern Leopard Frogs (Lithobates pipiens) in agricultural wetlands and assessed their survival. We used Passive Sampling Devices (PSDs) to test for differences in pesticide exposure among grassland, wetland, and agricultural habitats. We found that pesticide concentration analyzed from PSDs varied among habitat types (P < 0.01) with concentration greatest in agricultural habitats. Amphibians frequently used wetland habitats early in our study, and transitioned into grassland habitats later in the summer, using agricultural fields rarely. Number and concentration of pesticides were greatest in tissues collected in May, but few pesticides were detected in individuals captured in August (P < https://0.01 and P < https://0.01, respectively). Our results indicate risk of pesticide accumulation is highest in aquatic habitats earlier in the year.
Papers & Reports Survival estimates for the invasive American Bullfrog
Authors: P E Howell; Erin Muths; Brent H Sigafus; Blake R Hossack
Outlet: Amphibia-Reptilia
We used five years of capture mark-recapture data to estimate annual apparent survival of post-metamorphic bullfrogs in a population on the Buenos Aires National Wildlife Refuge in their invaded range in Arizona, U.S.A.
Papers & Reports A Synthesis of Evidence of Drivers of Amphibian Decline
Authors: Evan HC Grant; David AW Miller; Erin Muths
Outlet: Herpetologica
ABSTRACT:—Early calls for robust long-term time series of amphibian population data are now being realized after 25 years of focused research. Inference from individual studies and locations have contributed to a basic consensus on drivers of these declines. Until recently there were no large-scale syntheses of long-term time series to test hypotheses about the generality of factors driving population dynamics at broad spatial scales. Through the U.S. Geological Survey Powell Center for Analysis and Synthesis, we brought together a group of scientists to elucidate mechanisms underlying amphibian declines in North America and Europe. We used time series of field data collected across dozens of study areas to make inferences with these combined data using hierarchical and spatial models. We bring together results from four syntheses of these data to summarize our state of knowledge of amphibian declines, identify commonalities among the results that suggest further avenues of study, and suggest a way forward in addressing amphibian declines – by looking beyond specific drivers to how to achieve stability in remaining populations. The common thread of these syntheses is that declines are real but not ubiquitous, and that multiple factors drive declines but the relative importance of each factor varies among species, populations and regions. We also found that climate is an important driver of amphibian population dynamics. However, the sensitivity to change varies among species in ways unlikely to explain overall rates of decline. Thirty years after the initial identification of a major catastrophe for global biodiversity, the scientific community has empirically demonstrated the reality of the problem, identified putative causes, provided evidence of their impacts, invested in broader scale actions, and attempted meta-analyses to search out global drivers. We suggest an approach that focuses on key demographic rates that may improve amphibian population trends at multiple sites across the landscape.
Papers & Reports A Synthesis of Evidence of Drivers of Amphibian Declines
Authors: Evan HC Grant; David AW Miller; Erin Muths
Outlet: Herpetologica xx: xxx-xxx
ABSTRACT: Early calls for robust long-term time series of amphibian population data, stemming from discussion following the first World Congress of Herpetology, are now being realized after 25 yr of focused research. Inference from individual studies and locations have contributed to a basic consensus on drivers of amphibian declines. Until recently there were no large-scale syntheses of long-term time series data to test hypotheses about the generality of factors driving population dynamics at broad spatial scales. Through the U.S. Geological Survey’s Powell Center for Analysis and Synthesis, we brought together a group of scientists to elucidate mechanisms underlying amphibian declines in North America and Europe. We used time series of field data collected across dozens of study areas to make inferences with these combined data using hierarchical and spatial models. We bring together results from four syntheses of these data to summarize our state of knowledge of amphibian declines, identify commonalities that suggest further avenues of study, and suggest a way forward in addressing amphibian declines—by looking beyond specific drivers to how to achieve stability in remaining populations. The common thread of the syntheses is that declines are real but not ubiquitous, and that multiple factors drive declines but the relative importance of each factor varies among species, populations and regions. We also found that climate is an important driver of amphibian population dynamics. However, the direction and magnitude of sensitivity to change vary among species in ways unlikely to explain overall rates of decline. Thirty years after the initial identification of a major catastrophe for global biodiversity, the scientific community has empirically demonstrated the reality of the problem, identified putative causes, provided evidence of their impacts, invested in broader scale actions, and attempted meta-analyses to search out global drivers. We suggest an approach that focuses on key demographic rates that may improve amphibian population trends at multiple sites across the landscape.
Papers & Reports Effects of Snowpack, Temperature, and Disease on Demography in a Wild Population of Amphibians
Authors: Erin Muths; Blake R Hossack; Evan HC Grant; David S Pilliod; Brittany A Mosher
Date: 2020-06 | Outlet: Herpetologica
Understanding the demographic consequences of interactions among pathogens, hosts, and weather conditions is critical in determining how amphibian populations respond to disease and in identifying site-specific conservation actions that can be developed to bolster persistence of amphibian populations. We investigated population dynamics in Boreal Toads relative to abiotic (fall temperatures and snowpack) and biotic (the abundance of another anuran host and disease) characteristics of the local environment in Wyoming, USA. We used capture-recapture data and a multi-state model where state is treated as a hidden Markov process to incorporate disease state uncertainty and assess our a priori hypotheses. Our results indicate that snowpack during the coldest week of the winter is more influential to toad survival, disease transition probabilities, and the population-level prevalence of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) in the spring, than temperatures in the fall or the presence of another host. As hypothesized, apparent survival at low (i.e., <25 cm) snowpack (https://0.22 [CI: 0.15–0.31]) was lower than apparent survival at high snowpack (https://90.65 [CI: 0.50–0.78]). Our findings highlight the potential for local environmental factors, like snowpack, to influence disease and host persistence, and demonstrate the ecological complexity of disease effects on population demography in natural environments. This work further emphasizes the need for improved understanding of how climate change may influence the relationships among pathogens, hosts, and their environment for wild animal populations challenged by disease.
Papers & Reports Highly variable rates of survival to metamorphosis in wild boreal toads (Anaxyrus boreas boreas)
Authors: J Crockett; Larissa L Bailey; Erin Muths
Date: 2020-02 | Outlet: Population Ecology
Life history theory suggests that long-lived, pond-breeding amphibians should have low and highly variable early life-stage survival rates, but this theoretical expectation is often untested and the causes of variation are usually unknown. We evaluated the impact of hydroperiod, presence of a pathogen (Batrachochytrium dendrobatidis [Bd]), presence of a potential predator (cutthroat trout Oncorhychus clarki stomias), and whether animals had been reintroduced into a site, on survival of early life stages of boreal toads (Anaxyrus boreas boreas). We used a multi-state mark-recapture framework to estimate survival of boreal toad embryos from egg to metamorphosis at four sites over five years. We found substantial spatial and temporal variation in survival to metamorphosis and documented some evidence that monthly tadpole survival was lower in sites with Bd, and without trout, and at permanent sites. Our results support theories of amphibian life history, aid in the management of this species of conservation concern, and contribute to our knowledge of the ecology of the species. Additionally, we present methodology that allows practitioners to account for different lengths of time between sampling periods when estimating survival probabilities and which is especially applicable to organisms with distinct biological stages.
Papers & Reports Batrachochytrium salamandrivorans (Bsal) not detected in an intensive survey of wild North American amphibians
Authors: Hardin J Waddle; Daniel A Grear; Brittany A Mosher; G ra Campbell; Michael J Adams; Adam R Backlin; William J Barichivich; Adrianne B Brand; Gary Bucciarelli; Daniel L Calhoun; T Chestnut; J M Davenport; A Dietrich; Robert N Fisher; Brad M Glorioso; Brian J Halstead; Marc P Hayes; R K Honeycutt; Blake R Hossack; Patrick M Kleeman; J A Lemos-Espinal; Jeffrey M Lorch; Brome McCreary; Erin Muths; Christopher A Pearl; Katherine LD Richgels; C W Robinson; Mark F Roth; Jennifer C Rowe; Walt J Sadinski; Brent H Sigafus; I Stasiak; S Sweet; Susan C Walls; C J Watkins-Colwell; C Le White; L A Williams; Megan E Winzeler
Date: 2020-08-03 | Outlet: Scientific Reports 10:13012
Papers & Reports Conservation decisions under pressure: lessons from an exercise in rapid response to wildlife disease
Authors: Stefano Canessa; Annemarieke Spitzen-van der Sluijs; Tariq Stark; Bryony E Allen; Phillip J Bishop; Molly Bletz; Cheryl J Briggs; David R Daversa; Matthew J Gray; Richard A Griffiths; Reid N Harris; Xavier A Harrison; Jason T Hoverman; Phillip Jervis; Erin Muths; Deanna H Olson; Stephen J Price; Corinne L Richards-Zawacki; Jacques Robert; Goncalo M Rosa; Ben C Scheele; Benedikt R Schmidt; Trenton WJ Garner
Date: 2019-12 | Outlet: Conservation Science and Practice
Novel outbreaks of emerging pathogens require rapid responses to enable successful mitigation. We simulated a one-day emergency meeting where experts were engaged to recommend mitigation strategies for a new outbreak of the fungal pathogen Batrachochytrium salamandrivorans in amphibians. Despite inevitable uncertainty, experts were able to suggest and discuss several possible strategies. However, their recommendations were undermined by imperfect definitions of the objectives and scope of management, a problem likely to arise in most real-world emergency situations. The exercise thus highlighted the importance of clearly defining the context, objectives, and spatial-temporal scale of mitigation decisions. Managers may feel under pressure to act immediately. However, an iterative process in which experts and managers cooperate to clarify objectives and uncertainties, while collecting more information and devising mitigation strategies, may be slightly more time consuming but ultimately lead to better outcomes.
News & Stories ARMI scientists participate in International Symposium: Amphibian population declines – 30 years of progress in confronting a complex problem. Montreal, Canada
Authors: Erin Muths; Evan HC Grant
September 27, 2019
Scientists first became concerned that the observations of declining or lost amphibian populations were not isolated incidents but were global in scope and severity at the landmark 1st World Congress of Herpetology in Canterbury England in 1989. The plight of amphibians became front-page news and the newly generated interest in their population biology generated a massive increase in our understanding of their ecology, epidemiology and conservation biology. To mark 30 years of research into amphibian population declines, the Redpath Museum and McGill University in Montreal held an international symposium on amphibian ecology and conservation biology to bring together many of the principle researchers now making significant advances in the field. Evan Grant and Erin Muths, Principle Investigators for ARMI, were invited participants to the symposium held in September. Dr. Grant presented a lecture on lessons from broad-scale synthetic analyses about drivers of decline and Dr. Muths presented on the effects of disease, temperature, and community on demography and how analytical advances allow us to address more complex questions about decline. Both topics will be featured manuscripts in the forthcoming special issue of the journal Herpetologica.