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284 record(s) found.

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 L 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.
Papers & Reports Late-season movement and habitat use by Oregon spotted frog (Rana pretiosa) in a large reservoir in Oregon, USA
Authors: Christopher A Pearl; Jennifer C Rowe; Brome McCreary; Michael J Adams
Date: 2022-03-04 | Outlet: Journal of Herpetology
Dam-created reservoirs are common landscape features that can provide habitat for amphibians, but their water level
fluctuations and nonnative predators can differ markedly from more natural habitats. We compared fall movement and habitat use by the
Oregon Spotted Frog (Rana pretiosa) in the reservoir pool with nearby river and pond habitats at Crane Prairie Reservoir in central
Oregon, USA. Movement rate of frogs in the river and ponds declined as water temperature cooled. Reservoir frogs moved further than
those in the river or ponds, and their movement rate increased as water temperature cooled. Most frog locations across all site types were
in aquatic herbaceous vegetation. We did not find shifts in habitat between early and late fall. Increased movement and the lack of
habitat shift in our reservoir frogs deeper into fall contrast with R. pretiosa in non-reservoir sites in this study and others. Consistent use
of vegetation by reservoir frogs throughout the fall could indicate cover use in presence of fish predators. Our study provides additional
detail on the range of habitats used by R. pretiosa in fall and suggests areas for further work to improve survival in constructed sites with
abundant fish predators.
Papers & Reports Effects of salinity and RU486 on waterborne aldosterone and corticosterone of larval northern leopard frog larvae
Authors: B J Tornabene; Creagh W Breuner; Blake R Hossack; E J Crespi
Date: 2022-02-01 | Outlet: General and Comparative Endocrinology
testIncreased salinity is an emerging contaminant of concern for aquatic taxa. For amphibians exposed to salinity, there is scarce information about the physiological effects and changes in osmoregulatory hormones such as corticosterone (CORT) and aldosterone (ALDO). Recent studies have quantified effects of salinity on CORT physiology of amphibians based on waterborne hormone collection methods, but much less is known about ALDO in iono- and osmoregulation of amphibians. We re-assayed waterborne hormone samples from a previous study to investigate effects of salinity (sodium chloride, NaCl) and a glucocorticoid receptor antagonist (RU486) on ALDO of northern leopard frog (Rana pipiens) larvae. We also investigated relationships between ALDO and CORT. Waterborne ALDO marginally decreased with increasing salinity and was, unexpectedly, positively correlated with baseline and stress-induced waterborne CORT. Importantly, ALDO increased when larvae were exposed to RU486, suggesting that RU486 may also suppress mineralocorticoid receptors or that negative feedback of ALDO is mediated through glucocorticoid receptors. Alternatively, CORT increases with RU486 treatment and might be a substrate for ALDO synthesis, which could account for increases in ALDO with RU486 treatment and the correlation between CORT and ALDO. ALDO was negatively correlated with percent water, such that larvae secreting more ALDO retained less water. Although sample sizes were limited and further validation and studies are warranted, our findings expand our understanding of adrenal steroid responses to salinization in amphibians and proposes new hypotheses regarding the co-regulation of ALDO and CORT.
Papers & Reports Hemidactylus parvimaculatus (Sri lankan Spotted House Gecko)
Authors: Christopher M Pellecchia; Brad M Glorioso; Robert W Mendyk; Charles A Collen; V Ch Montross; William McGighan; K Macedo; B R Maldonado; I N Morenc
Date: 2019-09-01 | Outlet: Herpetological Review
Describes three new parish records for this exotic species in Louisiana
Papers & Reports DIADOPHIS PUNCTATUS (Ring-necked Snake)
Authors: R P Kidder; Brad M Glorioso; Katie D Gray
Outlet: Herpetological Review
A new parish record for the Ring-necked Snake in Louisiana
Papers & Reports AMBYSTOMA OPACUM (Marbled Salamander). ATYPICAL NEST SITES.
Authors: Joshua M Hall; Brad M Glorioso; J Se Doody
Date: 2021-09-01 | Outlet: Herpetological Review
This note describes atypical locations where Marbled Salamanders, Ambystoma opacum, eggs have been laid off the substrate.
Papers & Reports Comparative Effects of Energy-Related Saline Wastewaters and NaCl on Hatching, Survival, and Fitness-Associated Traits of Two Amphibian Species
Authors: B J Tornabene; Creagh W Breuner; Blake R Hossack
Date: 2021 | Outlet: Environmental Toxicology and Chemistry
Increased salinity (sodium chloride; NaCl) is a prevalent and persistent
contaminant that negatively affects freshwater ecosystems. Although
most studies focus on effects of salinity from roads salts (primarily
NaCl), high-salinity wastewaters from energy extraction (wastewaters)
could be more harmful because they contain NaCl and other toxic
components. Many amphibians are sensitive to salinity and their eggs
are thought to be the most sensitive life history stage. However, there
are few investigations with salinity that include eggs and larvae
sequentially in long-term exposures. We investigated the relative effects
of wastewaters from a large energy reserve, the Williston Basin (USA),
and NaCl on northern leopard (Rana pipiens) and boreal chorus
(Pseudacris maculata) frogs. We exposed eggs to salinity and tracked
responses through larval stages (for 24 days). Wastewaters and NaCl
reduced hatching and larval survival, growth, development, and activity
while also increasing deformities. Chorus frog eggs and larvae were
more sensitive to salinity than leopard frogs suggesting species-specific
responses. Contrary to previous studies, eggs of both species were less
sensitive to salinity than larvae. Our ecologically relevant exposures
suggest that accumulating effects can reduce survival relative to starting
experiments with unexposed larvae. Alternatively, egg casings of some
species may provide some protection against salinity. Notably, effects of
wastewaters on amphibians were predominantly due to NaCl rather than
other components. Therefore, findings from studies with other sources of
increased salinity (e.g., road salts) could guide management of
wastewater-contaminated ecosystems, and vice versa, to mitigate
effects of salinization.
Papers & Reports Corticosterone Mediates a Growth-Survival Tradeoff for an Amphibian Exposed to Increased Salinity
Authors: B J Tornabene; Blake R Hossack; E J Crespi; Creagh W Breuner
Date: 2021-08-09 | Outlet: Journal of Experimental Zoology Part A
Life-history tradeoffs are common across taxa, but growth-survival tradeoffs—which usually enhance survival at a cost to growth—are less frequently investigated. Increased salinity (NaCl) is a prevalent anthropogenic disturbance that may cause a growth-survival tradeoff for amphibians. Although physiological mechanisms mediating tradeoffs are seldom investigated, hormones are prime candidates. Corticosterone (CORT) is a steroid hormone that independently influences survival and growth and may provide mechanistic insight into growth-survival tradeoffs. We used 24-d trials to test effects of salinity (0 – 4000 mg/L Cl-) on growth, development, survival, CORT responses, and tradeoffs among traits of larval Northern Leopard Frogs (Rana pipiens). We also tested experimentally suppressed CORT signaling to determine whether CORT signaling mediates effects of salinity and life history tradeoffs . Increased salinity reduced survival, growth, and development. Suppressing CORT signaling in conjunction with salinity reduced survival further, but also attenuated negative effects of salinity on growth and development. CORT of control larvae increased or was stable with growth and development, but decreased with growth and development for those exposed to salinity. Therefore, salinity dysregulated CORT physiology. Across all treatments, larvae that survived had higher CORT than larvae that died. By manipulating CORT signaling, we provide strong evidence that CORT physiology mediates the outcome of a growth-survival tradeoff. To our knowledge, this is the first study to concomitantly measure tradeoffs between growth and survival and experimentally link these changes to CORT physiology. Identifying mechanistic links between stressors and fitness-related outcomes is critical to enhance our understanding of tradeoffs.
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 L Muths; Brent H Sigafus; Blake R Hossack
Outlet: Copeia
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 L 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 L 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 Demography of the Oregon spotted frog along a hydrologically modified river
Authors: Jennifer C Rowe; Adam Duarte; Christopher A Pearl; Brome McCreary; P K Haggerty; John W Jones; Michael J Adams
Date: 2021-06-21 | Outlet: Ecosphere
Altered flow regimes can contribute to dissociation between life history strategies and environmental conditions, leading to reduced persistence reported for many wildlife populations inhabiting regulated rivers. The Oregon spotted frog (Rana pretiosa) is a threatened species occurring in floodplains, ponds, and wetlands in the Pacific Northwest with a core range in Oregon, USA. All life stages of R. pretiosa are reliant on aquatic habitats, and inundation patterns across the phenological timeline can have implications for population success. We conducted capture-mark-recapture (CMR) sampling of adult and subadult R. pretiosa at three sites along the Deschutes River downstream from two dams that regulate flows. We related the seasonal extent of inundated habitat at each site to monthly survival probabilities using a robust design CMR model. We also developed matrix projection models to simulate population dynamics into the future under current river flows. Monthly survival was strongly associated with the extent and variability of inundated habitat, suggesting some within-season fluctuations at higher water levels could be beneficial. Seasonal survival was lowest in the winter for all three sites, owing to limited water availability and the greater number of months within this season relative to other seasons. Population growth for the two river-connected sites was most strongly linked to adult survival, whereas population growth at the river-disconnected site was most strongly tied to survival in juvenile stages. This research identifies population effects of seasonally limited water and highlights conservation potential of enhancing survival of particularly influential life stages.
Papers & Reports New Parish Records for Louisiana Amphibians and Reptiles
Authors: Brad M Glorioso
Date: 2021-06-01 | Outlet: Herpetological Review
Dundee and Rossman (1989) published distribution maps of Louisiana herpetofaunal species in The Amphibians and Reptiles of Louisiana over 30 years ago. Since then many records have been published, mostly in Herpetological Review, documenting additions to these original maps. Though many are single species additions, several compilations of new Louisiana records have been published (Boundy 1994, 1998; 2004; Rosenzweig et al. 2007; Boundy and Gregory 2012; Battaglia et al. 2015). Here I report a total of 22 records that help to fill distributional gaps primarily in southern Louisiana. Most records are a result of targeted surveys during work projects or opportunistic encounters by the author. Those records where the author is not listed as an observer were submitted by others to the author via email. All records are photo vouchers deposited in the Florida Museum of Natural History (FMNH) Herpetology collection. Charles D. Battaglia of the Louisiana Department of Wildlife and Fisheries (LDWF) and Coleman Sheehy of the FMNH verified species identification. All records represent new parish records unless otherwise stated as determined by a list compiled by now-retired LDWF state herpetologist Jeff Boundy and through queries at https://VertNet.org. I thank Raymond P. Kidder for his assistance with querying https://VertNet.org. This is contribution number XXX of the U.S. Geological Survey Amphibian Research and Monitoring Initiative (ARMI).
Papers & Reports Abundance of Gulf Coast Waterdogs (Necturus beyeri) along Bayou Lacombe, Saint Tammany Parish, Louisiana
Authors: Brad M Glorioso; J Hardin Waddle; L J Muse; S T Godfrey
Date: 2021-06-11 | Outlet: Journal of Herpetology
Few ecological studies have been conducted on Gulf Coast Waterdogs (Necturus beyeri), and published studies have focused on relatively small stream sections of 125 m to https://1.75 km. In 2015, we sampled Gulf Coast Waterdogs at 25 locations along a 13.4-km stretch of Bayou Lacombe (Saint Tammany Parish, Louisiana, USA) to better understand factors that may influence the distribution of Gulf Coast Waterdogs within streams. We checked 250 unbaited traps once per week for three weeks and captured 170 Gulf Coast Waterdogs at 18 of the 25 sites. We used hierarchical models of abundance to estimate abundance at each site as a function of site covariates including pH, turbidity, and distance from headwaters. The abundance of Gulf Coast Waterdogs within Bayou Lacombe was highest toward the center of the segment of stream we sampled, but we found no evidence that pH or turbidity affected abundance within our study area. Site level abundance estimates of Gulf Coast Waterdogs ranged from 0 to 82, and we estimated that there were 767 (95% Bayesian credible interval [CRI]: 266–983) Gulf Coast Waterdogs summed across all 25 sampling sites. We derived an estimate of 6,321 (95% CRI: 2,139–15,922) Gulf Coast Waterdogs for the entire 13.4 km section of Bayou Lacombe, which includes our 25 sites and the adjoining stream reaches between our sites. Our results suggest that Gulf Coast Waterdogs may be uncommon or absent in the headwaters, possibly because of shallow water and swift currents with little preferred habitats, and prefer the middle stream reaches with adequate depth and an abundance of preferred microhabitats.
Papers & Reports Enigmatic Near-Extinction in a Boreal Toad Metapopulation in Northwestern Montana
Authors: Rebecca M McCaffery; Robin E Russell; Blake R Hossack
Outlet: Journal of Wildlife Management
North America’s protected lands harbor significant biodiversity and provide habitats where species threatened by a variety of stressors in other environments can thrive. Yet disease, climate change, and other threats are not limited by land management boundaries and can interact with conditions within protected landscapes to affect sensitive populations. We examined the population dynamics of a boreal toad (Anaxyrus boreas) metapopulation at a wildlife refuge in northwestern Montana over a 16-year period (2003-2018). We used robust design capture-recapture models to estimate male population size, recruitment, and apparent survival over time and in relation to the amphibian chytrid fungus, Batrachochytrium dendrobatidis. We estimated female population size in years with sufficient captures. Finally, we examined trends in male and female toad body size and condition. We found no evidence of an effect of disease or time on male toad survival but detected a strong negative trend in recruitment of new males to the population. Estimates of male and female abundance decreased dramatically over time. Body size of males and females was inversely related to estimated population size, consistent with reduced recruitment to replace adults, but body condition of adult males was only weakly associated with abundance. Together, these results describe the demography of a near-extinction event, and point to dramatic decreases in the recruitment of new individuals to the breeding population as the cause of this decline. We surmise that processes related to the restoration of historical hydrology within the refuge adversely affected amphibian breeding habitat, and that these changes interacted with disease, life history, and other factors to restrict the recruitment of new individuals to the breeding population over time. Our results point to challenges in understanding and predicting drivers of population change and highlight that current metrics for assessing population status can have limited predictive ability.
Papers & Reports Why disease ecology needs life-history theory: a host perspective
Authors: Andrés Valenzuela-Sánchez; M Wilbur; Stefano Canessa; Leonardo Bacigalupe; Erin L 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.
Papers & Reports Density dependence and adult survival drive dynamics in two high elevation amphibian populations
Authors: Amanda M Kissel; S Tenan; Erin L 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 Water Temperature and Availability Shape the Spatial Ecology of a Hot Springs Endemic Toad (Anaxyrus williamsi)
Authors: Brian J Halstead; Patrick M Kleeman; Jonathan P Rose; Kristen J Fouts
Date: 2021-02-26 | Outlet: Herpetologica
Desert amphibians are limited to exploiting ephemeral resources and aestivating or to inhabiting scarce refuges of permanent water, such as springs. Understanding how amphibians use these resources is essential for their conservation. Dixie Valley Toads (Anaxyrus williamsi) are precinctive to a small system of cold and hot springs in the Dixie Valley, Nevada, USA. The toads have been petitioned for listing under the US Endangered Species Act, and information about how they use terrestrial and aquatic resources will help managers to conserve the toads and identify threats like geothermal energy development that might affect these toads. We used radiotelemetry to study the seasonal home ranges, movements, and habitat associations of Dixie Valley Toads in autumn 2018 and spring 2019. We found that toads were very closely associated with water in both seasons, with most observations occurring in water, especially for males in spring and all toads in the autumn. Even when found in terrestrial habitat, toads were a median distance of 4.2 m (95% credible interval = 3.3–5.3) from water; 95% of the time in spring and autumn, toads were within 14 m of water. Dixie Valley Toad habitat selection indicated a similar pattern, with selection in both spring and autumn for locations closer to water and for warmer water and substrates than at nearby available locations. In autumn, toads also avoided bare ground and terrestrial graminoids. Dixie Valley Toads selected brumation sites in, over (within dense vegetation), or near water, often near springs where water depths and temperatures are likely stable through the winter. The reliance of Dixie Valley Toads on water in spring, autumn, and during brumation suggests that alteration to historical flows and water temperatures are likely to affect the toads. Changes to the hydrothermal environment when toads are brumating could be particularly detrimental, potentially killing inactive toads.
Papers & Reports Estimating the survival of unobservable life stages for a declining frog with a complex life-history.
Authors: Jonathan P Rose; Sarah J Kupferberg; Clara A Wheeler; Patrick M Kleeman; Brian J Halstead
Date: 2021-02-15 | Outlet: Ecosphere 12(2):e03381
Demographic models enhance understanding of drivers of population growth and inform conservation efforts to prevent population declines and extinction. For species with complex life histories, however, parameterizing demographic models is challenging because some life stages can be dif?cult to study directly. Integrated population models (IPMs) empower researchers to estimate vital rates for organisms that have cryptic or widely dispersing early life stages by integrating multiple demographic data sources. For a stream-inhabiting frog(Rana boylii) that is declining through much of its range in Oregon and California, USA, we collected egg-mass counts and capture–mark–recapture data on adults from two populations in California to ?t IPMs that estimate adult abundance and the survival rate of both marked and unobserved life stages. Estimates of adult abundance based on long-term monitoring of egg-mass counts showed that study populations ?uctuated greatly inter-annually but were stable at longer timescales (i.e., decades). Adult female survival during 5–6 yr of capture–mark–recapture study periods was nearly equal in each population. Survival rate of R. boylii eggs to the subadult stage is low on average (0.002) but highly variable among years depending on post-oviposition stream ?ow. Population viability analysis showed that survival of adult and subadult life stages has the greatest proportional effect on population growth; the survival of egg and tadpole life stages, however, is more malleable by management interventions. For example, simulations showed head-starting of tadpoles, salvaging stranded egg masses, and limiting aseasonal pulsed ?ows could dramatically reduce the threat of extirpation. This study demonstrates the value of integrating multiple demographic data sources to construct models of population dynamics in species with complex life histories.