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766 record(s) found.

Papers & Reports Inferential biases linked to unobservable states in complex occupancy models
Authors: Brittany A Mosher; Larissa L Bailey; B A Hubbard; Kathryn P Huyvaert
Date: 2017-02 | Outlet: Ecography DOI: 10.1111/ecog.02849
Our work is motivated by the impacts of the emerging infectious disease chytridiomycosis, a disease of amphibians that associated with declines of many species worldwide. Using this host-pathogen system as a general example, we first illustrate how misleading inferences can result from failing to incorporate pathogen dynamics into the modeling process, especially when the pathogen is difficult or impossible to survey in the absence of a host species. We found that traditional modeling techniques can underestimate the effect of a pathogen on host species occurrence and dynamics when the pathogen can only be detected in the host, and pathogen information is treated as a covariate. We propose a dynamic multistate modeling approach that is flexible enough to account for the detection structures that may be present in complex multistate systems, especially when the sampling design is limited by a species’ natural history or sampling technology.
Papers & Reports Amphibians, pesticides, and the amphibian chytrid fungus in resetored weltands in agricultural landscapes
Authors: Rebecca A Reeves; Clay L Pierce; M Vandever; Erin Muths; K L Smalling
Date: 2017 | Outlet: Herpetological Conservation and Biology 12:68-77
Information on interactions between pesticide exposure and disease prevalence in amphibian populations is limited, especially from field data.Exposure to certain herbicides and insecticides has the potential to decrease immune response in frogs which can potentially lead to an increased abundance of Batrachochytrium dendrobatidis (Bd) zoospores on individuals and in the wetlands.In contrast, exposure to certain fungicides can decrease Bd abundance on frog skin. We examined the relationships between the abundance of Bd on the skin of individual Boreal Chorus Frogs(Pseudacris maculata) and the concentrations of pesticides in the water and in frog tissue at six agriculturally dominated wetlands in Iowa, USA
Papers & Reports Occurrence of Amphibians in Northern California Coastal Dune Drainages
Authors: Brian J Halstead; Patrick M Kleeman
Date: 2017-07 | Outlet: Northwestern Naturalist 98(2):91-100
Many coastal dune ecosystems have been degraded by non-native dune vegetation, but these systems might still provide valuable habitat for some taxa, including amphibians. Because restoration of degraded dune systems is occurring and likely to continue, we examined the occurrence of amphibians in drainages associated with a coastal dune ecosystem degraded by invasive plants (European Beachgrass, Ammophila arenaria, and Iceplant, Carpobrotus edulis). We found that occupancy of 3 amphibian species (California Red-legged Frog, Rana draytonii; Sierran Treefrog, Hyliola sierra; and Rough-skinned Newt, Taricha granulosa) among 21 coastal dune drainages was high, with most coastal dune drainages occupied by all 3 species. Furthermore, reproduction of Sierran Treefrogs and California Red-legged Frogs was estimated to occur in approximately 1/2 and 1/3; of the drainages, respectively. The probability of occurrence of Rough-skinned Newts and pre-metamorphic life stages of both anurans decreased during the study, perhaps because of ongoing drought in California or precipitation-induced changes in phenology during the final year of the study. Maintaining structural cover and moist features during dune restoration will likely benefit native amphibian populations inhabiting coastal dune ecosystems.
Papers & Reports Informing recovery in a human-transformed landscape: drought-mediated coexistence alters population trends of an imperiled salamander and invasive predators
Authors: Blake R Hossack; R K Honeycutt; Brent H Sigafus; Erin Muths; C L Crawford; T R Jones,; J A Sorensen; James C Rorabaugh; Thierry C Chambert
Date: 2017-03-16 | Outlet: Biological Conservation 209 (2017) 377–394
Understanding the additive or interactive threats of habitat transformation and invasive species is critical for conservation, especially where climate change is expected to increase the severity or frequency of drought. In the arid southwestern USA, this combination of stressors has caused widespread declines of native aquatic and semi-aquatic species. Achieving resilience to drought and other effects of climate change may depend upon continued management, so understanding the combined effects of stressors is important. We used Bayesian hierarchical models fitted with 10-yrs of pond-based monitoring surveys for the federally-endangered Sonoran Tiger Salamander (Ambystoma mavortium stebbinsi) and invasive predators (fishes and American Bullfrogs, Lithobates catesbeianus) that threaten native species. We estimated trends in occupancy of salamanders and invasive predators while accounting for hydrological dynamics of ponds, then used a two-species interaction model to directly estimate how invasive predators affected salamander occupancy. We also tested a conceptual model that predicted that drought, by limiting the distribution of invasive predators, could ultimately benefit native species. Even though occupancy of invasive predators was stationary and their presence in a pond reduced the probability of salamander presence by 23%, occupancy of Sonoran Tiger Salamanders increased, annually, by 2.2%. Occupancy of salamanders and invasive predators both declined dramatically following the 5th consecutive year of drought. Salamander occupancy recovered quickly after return to non-drought conditions, while occupancy of invasive predators remained suppressed. Models that incorporated three time-lagged periods (1 to 4 yrs) of local moisture conditions confirmed that salamanders and invasive predators responded differently to drought, reflecting how life-history strategies shape responses to disturbances. The positive 10-yr trend in salamander occupancy and their rapid recovery after drought provided partial support for the hypothesis of drought-mediated coexistence with invasive predators. These results also suggest management opportunities for conservation of the Sonoran Tiger Salamander and other imperiled organisms in human-transformed landscapes.
Papers & Reports Frogs on the Beach: Ecology of California Red-Legged Frogs (Rana draytonii) in Coastal Dune Drainages
Authors: Brian J Halstead; Patrick M Kleeman
Date: 2017-04-30 | Outlet: Herpetological Conservation and Biology 12:127–140
California Red-legged Frogs (Rana draytonii) are typically regarded as inhabitants of permanent ponds, marshes, and slow-moving streams, but their ecology in other habitats, such as drainages among coastal dunes, remains obscure. Because coastal dune ecosystems have been degraded by development, off-highway vehicle use, stabilization, and invasive species, these unique ecosystems are the focus of restoration efforts. To better understand the ecology of California Red-legged Frogs in coastal dune ecosystems and to avoid and minimize potential negative effects of dune restoration activities on these rare frogs, we studied their spatial ecology, habitat selection, and survival in coastal dune drainages at Point Reyes National Seashore, California, USA. All 22 radio-marked frogs remained in their home drainages throughout the spring and summer of 2015 and, with some notable exceptions, most remained close to water. Local convex hull home ranges of four out of five California Red-legged Frogs with > 20 observations in dunes were < 1,600 m2. At the population level, frogs were 1.7 (1.2-4.4) times more likely to select sites 1 m closer to water, and were 83 (2.0-17,000) times more likely to select sites with 10% greater percent cover of logs that served as refuges from environmental extremes and predators. On average, California Red-legged Frogs avoided the invasive plants Iceplant (Carpobrotus edulis) and European Beachgrass (Ammophila arenaria). Frogs were 0.68 (0.32-0.89) and 0.55 (0.24-0.75) times as likely to select areas that had 10% greater cover of these plants, respectively. Assuming constant risk of mortality, California Red-legged Frogs had an annual survival rate of 0.70 (range, 0.27-0.96) in coastal dune drainages. This relatively high survival rate suggests that coastal dune drainages provide a locally important habitat for California Red-legged Frogs. Restoration practices that maintain wetted drainages with logjams are likely to benefit California Red-legged Frogs.
Papers & Reports Structured decision making as a conservation tool for recovery planning of two endangered salamanders
Authors: Katherine M O'Donnell; Arianne F Messerman; William J Barichivich; Raymond D Semlitsch; Thomas A Gorman; Harold G Mitchell; Nathan L Allan; Dante B Fenolio; Adam W Green; Fred A Johnson; Allison C Keever; Mark Mandica; Julien A Martin; Jana Mott; Terry Peacock; Joseph Reinman; Stephanie S Romanach; Greg Titus; Conor P McGowan; Susan C Walls
Date: 2017 | Outlet: Journal for Nature Conservation 37:66-72.
At least one-third of all amphibian species face the threat of extinction, and current amphibian extinction rates are four orders of magnitude greater than background rates. Preventing extirpation often requires both ex situ (i.e., conservation breeding programs) and in situ strategies (i.e., protecting natural habitats). Flatwoods salamanders (Ambystoma bishopi and A. cingulatum) are protected under the U.S. Endangered Species Act. The two species have decreased from 476 historical locations to 63 recently extant locations (86.8% loss). Recovery efforts are needed to increase populations and prevent extinction, but uncertainty regarding optimal actions in both ex situ and in situ realms hinders recovery planning. We used structured decision making (SDM) to address key uncertainties regarding captive breeding and habitat restoration, and developed short-, medium-, and long-term goals to achieve recovery objectives. In promoting a transparent, logical approach, SDM has proven vital for developing recovery plans for flatwoods salamanders. The SDM approach has clear advantages over other previous approaches to recovery efforts, and should be considered for other complex decisions regarding endangered species.
Papers & Reports A Discrete Stage-Structured Model of California Newt Population Dynamics During a Period of Drought
Authors: M T Jones; W R Millligan; L B Kats; T L Vandergon; R L Honeycutt; Robert N Fisher; Courtney L Davis; T A Lucas
Date: 2017 | Outlet: Journal of Theoretical Biology 414:245-253
We introduce a mathematical model for studying the population dynamics under drought of the California newt (Taricha torosa), a species of special concern in the state of California. Since 2012, California has experienced a record-setting drought, and multiple studies predict drought conditions currently underway will persist and even increase in severity. Recent declines and local extinctions of California newt populations in Santa Monica Mountain streams motivate our study of the impact of drought on newt population sizes. Although newts are terrestrial salamanders, they migrate to streams each spring to breed and lay eggs. Since egg and larval stages occur in water, a precipitation deficit due to drought conditions reduces the space for newt egg-laying and the necessary habitat for larval development. To mathematically forecast newt population dynamics, we develop a nonlinear system of discrete equations that includes demographic parameters such as survival rates for newt life stages and egg production, which depend on habitat availability and rainfall. We estimate these demographic parameters using 15 years of stream survey data collected from Cold Creek in Los Angeles County, California, and our model captures the observed decline of the parameterized Cold Creek newt population. Based upon data analysis, we predict how the number of available newt egg-laying sites varies with annual precipitation. Our model allows us to make predictions about how the length and severity of drought can affect the likelihood of persistence and the time to critical endangerment of a local newt population. We predict that sustained severe drought will critically endanger the newt population but that the newt population can rebound if a drought is sufficiently short.
Papers & Reports Identifying small depressional wetlands and using a topographic position index to infer hydroperiod regimes for pond-breeding amphibians
Authors: Jeffrey W Riley; Daniel L Calhoun; William J Barichivich; Susan C Walls
Date: 2017-01-17 | Outlet: Wetlands 37(2):325-228.
Small, seasonal pools and temporary ponds (<4.0ha) are the most numerous and biologically diverse wetlands in many natural landscapes. Thus, accurate determination of their numbers and spatial characteristics is beneficial for conservation and management of biodiversity associated with these freshwater systems. We examined the utility of a topographic position index (TPI) landscape classification to identify and classify depressional wetlands. We also assessed relationships between topographic characteristics and ponded duration of known wetlands to allow hydrological characteristics to be extended to non-monitored locations. Our results indicate that this approach was successful at identifying wetlands, but did have higher errors of commission (10%) than omission (5%). Additionally, the TPI procedure provided a reasonable means to correlate general ponded duration characteristics (long/short) with wetland topography. Although results varied by hydrologic class, permanent/long ponded duration wetlands were more often classified correctly (80%) than were short ponded duration wetlands (67%). However, classification results were improved to 100% and 75% for permanent/long and short ponded duration wetlands, respectively, by removing wetlands occurring on an abrupt marine terrace that erroneously inflated pond topographic characteristics. Our study presents an approach for evaluating wetland suitability for species or guilds that are associated with key habitat characteristics, such as hydroperiod.
Papers & Reports A Framework for Modeling Emerging Diseases to Inform Management
Authors: Robin E Russell; Evan HC Grant; R A Katz; Katherine LD Richgels; D P Walsh,
Outlet: Emerging Infectious Diseases
The rapid emergence and reemergence of zoonotic diseases requires the ability to rapidly evaluate and implement optimal management decisions. Actions to control or mitigate the effects of emerging pathogens are commonly delayed because of uncertainty in the estimates and the predicted outcomes of the control tactics. The development of models that describe the best known information regarding the disease system at the early stages of disease emergence is an essential step for optimal decision-making. Models can predict the potential effects of the pathogen, provide guidance for assessing the likelihood of success of different proposed management actions, quantify the uncertainty surrounding the choice of the optimal decision, and highlight critical areas for immediate research. We demonstrate how to develop models that can be used as a part of a decision-making framework to determine the likelihood of success of different management actions given current knowledge.
Papers & Reports Potential concerns with analytical methods used for the detection of Batrachochytrium salamandrivorans from archived DNA of amphibian swab samples, Oregon, USA
Authors: D Iwanowicz; W Schill; Deanna H Olson; Michael J Adams; C L Densmore; R Cornman; Cynthia Adams; C Figiel; Chauncey W Anderson; Andrew R Blaustein; T Chestnut
Date: 2017 | Outlet: Herpetological Review 48:352-355
Papers & Reports Additive impacts of experimental climate change increase risk to an ectotherm at the Arctic’s edge
Authors: J M Davenport; Blake R Hossack; L Fishback
Outlet: Global Change Biology
Globally, Arctic and Subarctic regions have experienced the greatest temperature increases during the last 30 years. These extreme changes have amplified threats to the freshwater ecosystems that dominate the landscape in many areas by altering water budgets. Several studies in temperate environments have examined the adaptive capacity of organisms to enhance our understanding of the potential repercussions of warming and associated accelerated drying for freshwater ecosystems. However, few experiments have examined these impacts in Arctic or Subarctic freshwater ecosystems, where the climate is changing most rapidly. To evaluate the capacity of a widespread ectotherm to anticipated environmental changes, we conducted a mesocosm experiment with wood frogs (Rana sylvatica) in the Canadian Subarctic. Three warming treatments were fully crossed with three drying treatments to simulate a range of predicted changes in wetland environments. We predicted wetland warming and drying would act synergistically, with water temperature partially compensating for some of the negative effects of accelerated drying. Across all drying regimes, a 1°C increase in water temperature increased the odds of survival by 1.79, and tadpoles in 52-day and 64-day hydroperiod mesocosms were 4.1–4.3 times more likely to survive to metamorphosis than tadpoles in 45-day mesocosms. For individuals who survived to metamorphosis, there was only a weak negative effect of temperature on size. As expected, increased temperatures accelerated tadpole growth through day 30 of the experiment. Our results reveal that one of the dominant herbivores in Subarctic wetlands, wood frog tadpoles, are capable of increasing their developmental rates in response to increased temperature and accelerated drying, but only in an additive manner. The strong negative effects of drying on survival, combined with lack of compensation between these two environmental drivers, suggest changes in the aquatic environment that are expected in this ecosystem will reduce mean fitness of populations across the landscape.
Papers & Reports Even with forewarning, challenges remain in developing a proactive response to emerging infectious diseases
Authors: Evan HC Grant; Erin Muths; R A Katz; Stefano Canessa; Michael J Adams; Jennifer R Ballard; Lee Berger; Cheryl J Briggs; J H Coleman; M J Gray; M Ca Harris; Reid N Harris; Blake R Hossack; Kathryn P Huyvaert; Jonathan E Kolby; Karen R Lips; Robert E Lovich; Hamish I McCallum; Joseph R Mendelson III; Priya Nanjappa; Deanna H Olson; Jenny G Powers; Katherine LD Richgels; Robin E Russell; Benedikt R Schmidt
Outlet: Frontiers in Ecology and Evolution
Despite calls for improving responses to emerging infectious diseases of wildlife, management is seldom considered until a disease has been detected in affected populations. Reactive approaches may limit the potential for control and increase total response costs. An alternative, proactive, management framework can identify immediate actions that reduce future impacts even before a disease is detected, as well as prepare actions conditional on disease emergence. We identify four main challenges to developing proactive management strategies for the newly discovered salamander pathogen, Batrachochytrium salamandrivorans (Bsal). Given that deep uncertainty is a hallmark of wildlife disease management and decisions are often complicated by multiple competing objectives, we advocate using decision analysis to create and evaluate trade-offs among proactive (pre-emergence) and reactive (post-emergence) management. Using principles from decision analysis, natural resources agencies and policy-makers can utilize a variety of tools to improve the development of management strategies for emerging infectious diseases.
Papers & Reports Evaluating within-population variability in behavior and demography for the adaptive potential of a dispersal-limited species to climate change.
Authors: David J Muñoz; K M Hesed; Evan HC Grant; David AW Miller
Outlet: Ecology and Evolution
Multiple pathways exist for species to respond to changing climates. However, responses of dispersal-limited species will be more strongly tied to ability to adapt within existing populations as rates of environmental change will likely exceed movement rates. Here, we assess adaptive capacity in Plethodon cinereus, a dispersal-limited woodland salamander. We quantify plasticity in behavior and variation in demography to observed variation in environmental variables over a 5 year period. We found strong evidence that temperature and rainfall influence P. cinereus surface presence, indicating changes in climate are likely to affect seasonal activity patterns. We also found that warmer summer temperatures reduced individual growth rates into the autumn, which is likely to have negative demographic consequences. Reduced growth rates may delay reproductive maturity and lead to reductions in size-specific fecundity, potentially reducing population level persistence. To better understand within-population variability in responses, we examined differences between two common color morphs. Previous evidence suggests that the color polymorphism may be linked to physiological differences in heat and moisture tolerance. We found only moderate support for morph-specific differences for the relationship between individual growth and temperature. Measuring environmental sensitivity to climatic variability is the first step in predicting species’ responses to climate change. Our results suggest phenological shifts and changes in growth rates are likely responses under scenarios where further warming occurs, and we discuss possible adaptive strategies for resulting selective pressures. &amp;#8195;
Papers & Reports Amphibian conservation: clarifications to comments from Andreone
Authors: Erin Muths; Robert N Fisher
Date: 2017
We appreciate the review and comments from Andreone (2016) regarding our proposed alternative strategy for addressing the amphibian crisis. Andreone recognizes the utility of an incident command system approach but doubts the feasibility of implementation at an international level. We stated in our original article, however, that ‘The feasibility of our suggestion is debatable, but our point is that radically different approaches are necessary to effectively manage the largest extinction event in modern history’
Papers & Reports SURGICAL TECHNIQUE FOR THE PLACEMENT OF INTRACOELOMIC RADIO TRANSMITTERS AND EXTERNAL SILICONE PASSIVE SAMPLING DEVICES FOR NORTHERN LEOPARD FROGS (Lithobates pipiens )
Authors: T Yaw; J E Swanson; Clay L Pierce; Erin Muths; K L Smalling; M Vandever; B A Zaffarano
Date: 2017 | Outlet: Journal of Herpetological Medicine and Surgery
Amphibians are excellent sentinels for contaminant exposure in prairie wetlands. Development of passive sampling devices (PSD) has greatly improved in recent years, and they present an innovative sampling technology that can potentially yield individual-specific, quantifiable data on chemical exposure. In this study, PSDs were attached to the ventral skin of 20 northern leopard frogs (Lithobates pipiens) with polypropylene sutures after radio transmitters had been surgically inserted into the coleomic cavity. After a recovery period frogs were released into the wild and located daily using radio telemetry to assess how long PSDs would remain attached in the frogs’ natural habitat. After one week, PSDs remained on 18 of the original 20 frogs. At 2 weeks 16 frogs were recovered and no PSDs remained attached. Although valuable data can be obtained over a short time period, more research will be necessary to demonstrate effectiveness of externally attaching silicone PSDs to northern leopard frogs for time periods longer than 1-2 weeks.
Papers & Reports RARE ALLUVIAL SANDS OF EL MONTE VALLEY, CALIFORNIA (SAN DIEGO COUNTY) SUPPORT HIGH HERPETOFAUNAL SPECIES RICHNESS AND DIVERSITY, DESPITE SEVERE HABITAT DISTURBANCE
Authors: Jonathan Q Richmond; Carlton J Rochester; N W Smith; J A Nordland; Robert N Fisher
Date: 2016 | Outlet: Southwest Naturalist 61:294-306
We characterized the species richness, diversity and distribution of amphibians and reptiles inhabiting El Monte Valley, a heavily disturbed, alluvium-filled basin within the lower San Diego River in Lakeside, California. This rare habitat type in coastal southern California is designated as a critical sand resource by the State of California (California Geological Survey) and is currently under consideration for a large-scale sand mining operation with subsequent habitat restoration. We conducted field surveys in the valley from June 2015-May 2016 and placed emphasis on detecting the coastal form of the California glossy snake (Arizona elegans occidentalis) given its status as a species of special concern by the California Department of Fish and Wildlife, its preference for sandy/gravelly habitats, and its documented historical presence in the valley. Survey techniques included drift fence lines with funnel traps, cover board arrays, walking transects, and road driving. We recorded 1,208 total captures in five sampling sections extending across the valley floor, revealing high species richness and diversity but with marked unevenness in species’ abundances. Two species are covered in the San Diego Multiple Species Conservation Program and 10 are listed as species of special concern in California. Snakes were the most species rich taxonomic group (13 species representing 11 genera), followed by lizards (11 species representing nine genera). Next to the southern Pacific rattlesnake (Crotalus oreganus helleri), A. e. occidentalis was the second most frequently detected snake species (n = 23 captures). Amphibian species richness was limited to two species of toad and one frog. Despite the relatively limited 12-month sampling period, a longstanding drought, and severe habitat disturbance, our study demonstrates that El Monte Valley harbors a rich herpetofauna that includes a number of sensitive species, including the largest known concentration of A. e. occidentalis in coastal San Diego County.
Papers & Reports Overcoming Roadblocks to Recovery of Declining Amphibian Populations in the United States
Authors: Susan C Walls; Lianne Ball; William J Barichivich; K M Enge; Thomas A Gorman; J G Palis; Raymond D Semlitsch; C K Dodd; Katherine M O'Donnell
Date: 2016-12-09 | Outlet: BioScience 67(2):156-165.
The U.S. Endangered Species Act of 1973 (ESA) affords many potential benefits to species threatened with extinction. Yet, most at-risk amphibians – one of the most imperiled vertebrate groups – remain unlisted under provisions of the ESA, and many impediments to recovery exist for those species that have been listed. Of the 35 U.S. amphibian species and distinct population segments (DPS) listed under the ESA, 28.6% currently lack a final (completed) recovery plan, 40% lack designated critical habitat, and 8.5% lack both. For species/DPS that have recovery plans, time between listing and development of those plans was from 2 to 29 years, and the time between listing and designation of critical habitat ranged from 0 to 14 years. The underlying causes of such delays in protection are complex and constitute roadblocks to recovery of imperiled species. We outline a series of strategic actions by which these roadblocks may be overcome.
Papers & Reports Amphibian dynamics in constructed ponds on a wildlife refuge: developing expected responses to hydrological restoration
Authors: Blake R Hossack
Date: 2016 | Outlet: Hydrobiologia
Management actions are based upon predictable responses. To form expected responses to restoration actions, I estimated habitat relationships and trends (2002&amp;#8210;2015) for four pond-breeding amphibians on a wildlife refuge (Montana, USA) where changes to restore historical hydrology to the system greatly expanded (&amp;#8805;8 times) the flooded area of the primary breeding site for western toads (Anaxyrus boreas). Additional restoration actions are planned for the near future, including removing ponds that provide amphibian habitat. Multi-season occupancy models based on data from 15 ponds sampled during 7 years revealed that the number of breeding subpopulations increased modestly for Columbia spotted frogs (Rana luteiventris) and was stationary for long-toed salamanders (Ambystoma macrodactylum) and Pacific treefrogs (Pseudacris regilla). For these three species, pond depth was the characteristic that was associated most frequently with occupancy or changes in colonization and extinction. In contrast, a large decrease in colonization by western toads explained the decline from eight occupied ponds in 2002 to two ponds in 2015. This decline occurred despite an increase in wetland area and the colonization of a newly-created pond. These changes highlight the challenges of managing for multiple species and how management responses can be unpredictable, possibly reducing the efficacy of targeted actions.
Papers & Reports Large-scale recovery of an endangered amphibian despite ongoing exposure to multiple stressors
Authors: R A Knapp; Gary M Fellers; Patrick M Kleeman; David AW Miller; V T Vredenburg; E B Rosenblum; Cheryl J Briggs
Date: 2016-10-03 | Outlet: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.1600983113
Amphibians are one of the most threatened animal groups, with 32% of species at risk of extinction. Given this, is the disappearance of a large fraction of the Earth’s amphibians inevitable, or are some declining species more resilient than is generally assumed? We address this question in a species that is emblematic of many declining amphibians, the endangered Sierra Nevada yellow-legged frog (Rana sierrae). Based on >7,000 frog surveys conducted across Yosemite National Park over a 20-year period, we show that after decades of decline and despite ongoing exposure to multiple stressors including introduced fish, the recently emerged disease chytridiomycosis, and pesticides, R. sierrae abundance increased 7-fold during the study and at a rate of 11% per year. These increases occurred in hundreds of populations throughout Yosemite, providing a rare example of amphibian recovery at an ecologically relevant spatial scale. Results from a laboratory experiment indicate that these increases may be due in part to reduced frog susceptibility to chytridiomycosis. The disappearance of nonnative fish from numerous water bodies following cessation of stocking also contributed to the recovery. The large-scale increases in R. sierrae abundance we document suggest that when habitats are relatively intact and stressors are reduced in their importance by active management or species’ adaptive responses declines of some amphibian may be partially reversible, at least at a regional scale. Other studies conducted over similarly large temporal and spatial scales are critically needed to provide insight and generality about the reversibility of amphibian declines at a global scale.
Papers & Reports Estimating occurrence and detection probabilities for stream-breeding salamanders in the Gulf Coastal Plain
Authors: J Y Lamb; J Hardin Waddle; C P Qualls
Date: 2017-03 | Outlet: Journal of Herpetology 51:102-108
Large gaps exist in our knowledge of the ecology of stream-breeding plethodontid salamanders in the Gulf Coastal Plain. Data describing where these salamanders are likely to occur along environmental gradients, as well as their likelihood of detection, are important for the prevention and management of amphibian declines. We used presence/absence data from leaf litter bag surveys and a hierarchical Bayesian multispecies single-season occupancy model to estimate the occurrence of five species of plethodontids across reaches in headwater streams in the Gulf Coastal Plain. Average detection probabilities were high (range = 0.432-0.942) and unaffected by sampling covariates specific to the use of litter bags (i. e., bag submergence, sampling season, in-stream cover). Estimates of occurrence probabilities differed substantially between species (range = 0.092-0.703) and were influenced by the size of the upstream drainage area and by the maximum proportion of the reach that dried. The effects of these two factors were not equivalent across species. Our results demonstrate that hierarchical multispecies models successfully estimate occurrence parameters for both rare and common streambreeding plethodontids. The resulting models clarify how species are distributed within stream networks, and they provide baseline values that will be useful in evaluating the conservation statuses of plethodontid species within lotic systems in the Gulf Coastal Plain.