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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 ½ and ⅓ 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.

During the summers of 2015 and 2018, we observed predation on Foothill Yellow-legged Frogs (Rana boylii) by a giant water bug (Abedus indentatus), a California Red-legged Frog (Rana draytonii), and a Diablo Range Gartersnake (Thamnophis atratus zaxanthus) adjacent to 3 separate isolated pools along intermittent reaches of Coyote Creek, Santa Clara County, California, USA. To the best of our knowledge, our observations provide the first published record of California Red-legged Frog and giant water bug preying upon Foothill Yellow-legged Frogs. As pool habitat contracts over the course of the dry season, locally abundant Yellow-legged Frogs may be increasingly vulnerable to predation from a suite of aquatic and terrestrial predators.

The need for efficient, accurate biodiversity monitoring is growing, especially for globally imperiled taxa, such as amphibians. Environmental DNA (eDNA) analysis holds enormous potential for enhancing monitoring programs, but as this tool is increasingly adopted, it is imperative for users to understand its potential benefits and shortcomings. We conducted a comparative study to evaluate the efficacy of two eDNA methodologies (quantitative (q)PCR and metabarcoding) and conventional field sampling approaches (seining, dipnetting, and visual encounter surveys) in a system of 20 ponds containing six different amphibian species. Using an occupancy modeling framework, we estimated differences in detection sensitivity across methods, with a focus on how eDNA survey design could be further optimized. Overall, both metabarcoding and qPCR were competitive with or improved upon conventional methods. Specifically, qPCR (species‐specific approach) was the most effective technique for detecting two rare species, the California tiger salamander (Ambystoma californiense) and California red‐legged frog (Rana draytonii), with a detection probability of >0.80 per survey. Metabarcoding (community approach) estimated amphibian diversity with comparable rates to field techniques on average, and detected an additional 41 vertebrate taxa. However, for two abundant species (western toads, Anaxyrus boreas, and Pacific chorus frogs, Pseudacris regilla), field techniques outperformed metabarcoding, especially as individuals metamorphosed. Our results indicate that eDNA approaches would be most effective when paired with visual encounter surveys to detect terrestrial life stages, and that more optimization, specifically primer choice and validation, is needed. By comparing methods across a diverse set of ponds and species, we provide guidance for future studies integrating eDNA approaches into amphibian monitoring.

Effective species management requires knowledge of species distributions, but surveys for cryptic species near the boundaries of their geographical ranges can be difficult. We used environmental DNA (eDNA) and occupancy modeling to examine the distribution of Northern Red-legged Frogs (Rana aurora) and federally threatened California Red-legged Frogs (Rana draytonii) in a sample of 60 forested stream sites near where their ranges meet in southern Mendocino County, California, USA. For both species, the probability of occurrence (ψ) in forest streams in our study area was very low: California Red-legged Frog ψ was <0.01 (95% credible interval = <0.01–0.05), and Northern Red-legged Frog ψ was 0.07 (0.02–0.15). DNA from both species was found at 1 pond site, suggesting either co-occurrence or introgression. Our results suggest that abundance, stream use, or both are very low for red-legged frogs in forested streams in southern Mendocino County.

Effectively planning conservation introductions involves assessing the suitability of both donor and recipient populations, including the landscape of disease risk. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has caused extensive amphibian declines globally and may hamper reintroduction attempts. To determine Bd dynamics in potential source populations for conservation translocations of the threatened California red-legged frog ( Rana draytonii ) to Yosemite National Park, we conducted Bd sampling in two populations in the foothills of the Sierra Nevada Mountains, California, U.S.A. At one of two sites, we observed lethally high Bd loads in early post-metamorphic life stages and confirmed one chytridiomycosis-induced mortality, the first such report for this species. These results informed source population site selection for subsequent R . draytonii conservation translocations. Conservation efforts aimed at establishing new populations of R . draytonii in a landscape where Bd is ubiquitous can benefit from an improved understanding of risk through disease monitoring and ex situ infection studies.

Widespread alteration of natural hydrologic patterns by large dams combined with peak demands for power and water delivery during summer months have resulted in frequent aseasonal flow pulses in rivers of western North America. Native species in these ecosystems have evolved with predictable annual flood-drought cycles; thus, their likelihood of persistence may decrease in response to disruption of the seasonal synchrony between stable low-flow conditions and reproduction. We evaluated whether altered flow regimes affected 2 native frogs in California and Oregon (U.S.A.) at 4 spatial and temporal extents. We examined changes in species distribution over approximately 50 years, current population density in 11 regulated and 16 unregulated rivers, temporal trends in abundance among populations occupying rivers with different hydrologic histories, and within-year patterns of survival relative to seasonal hydrology. The foothill yellow-legged frog (Rana boylii), which breeds only in flowing water, is more likely to be absent downstream of large dams than in free-flowing rivers, and breeding populations are on average 5 times smaller in regulated rivers than in unregulated rivers. Time series data (range = 8 — 19 years) from 5 populations of yellow-legged frogs and 2 populations of California red-legged frogs (R. draytonii) across a gradient of natural to highly artificial timing and magnitude of flooding indicate that variability of flows in spring and summer is strongly correlated with high mortality of early life stages and subsequent decreases in densities of adult females. Flow management that better mimics natural flow timing is likely to promote persistence of these species and others with similar phenology. La alteración generalizada de los patrones hidrológicos debida a presas en combinación con la demanda de energía y agua durante el verano ha resultado en frecuentes pulsos de flujo atípicos en ríos de Norteamérica occidental. Las especies nativas en esos ecosistemas han evolucionado con los ciclos anuales predecibles de inundación-sequía; por lo tanto, sus probabilidades de persistencia puede decrecer en respuesta a la disrupción de la sincronía estacional entre condiciones de bajo flujo estable y la reproducción. Evaluamos si los regímenes de flujo alterados afectaron a 2 especies de ranas nativas en California y Oregon (E.U.A.) en cuatro extensiones espaciales y temporales. Examinamos la distribución de especies a lo largo de casi 50 años, la densidad poblacional actual en 11 ríos regulados y 16 no regulados, las tendencias temporales en la abundancia de poblaciones ocupando ríos con historias hidrológicas diferentes, y los patrones anuales de supervivencia en relación con la hidrología estacional. Rana boylii, que se reproduce solo en agua corriente, tiene mayor probabilidad de ausencia río debajo de presas grandes que en ríos con flujo libre, y las poblaciones reproductivas en ríos regulados son en promedio 5 veces que en ríos no regulados. Los datos de series de tiempo (rango = 8-19 años) de 5 poblaciones de R. boylii y 2 poblaciones de R. draytonii a lo largo de gradientes de sincronía estacional y magnitud de inundación desde naturales hasta altamente artificales indican que la variabilidad de flujos en primavera y verano esta fuertemente con elevada mortalidad en las primeras etapas de vida y subsecuentes disminución en la densidad de hembras adultas. Es probable que el manejo de flujos que mejor se asemeje a la sincronía natural promueva la persistencia de estas especies y otras con fenología similar.

Southern California has experienced widespread amphibian declines since the 1960s. One species, the Vulnerable California red-legged frog Rana draytonii, is now considered to be extirpated from most of southern California. In February 2017 a population of R. draytonii was discovered in the southern foothills of the San Bernardino Mountains of Riverside County, California, near the edge of the species’ historical distribution. This population belongs to an mtDNA lineage that was presumed to be extirpated within the USA but is still extant in Baja California, Mexico. This discovery increases the potential for future, evolutionarily informed translocations within the southern portion of this species’ range in California.

Establishing historical species distributions can assist conservation translocations for threatened species, and yet, ecological changes necessitate developing restoration targets that are not analogous to historical baselines. Despite its recent conservation translocation to Yosemite Valley in Yosemite National Park, Sierra Nevada Mountains, USA, the historical distribution of the federally threatened California Red-legged Frog (Rana draytonii) in the valley remains unclear. Using archival records, interviews, and museum specimens, we examined the historical evidence for California Red-legged Frogs and sympatric amphibian species in the Yosemite region. We found a paucity of reliable amphibian records for Yosemite Valley since the 19th century, one of the most-visited sites in the US National Park System, and conclude that this is the result of historically low collecting and survey effort prior to the introduction of invasive American Bullfrogs (Lithobates catesbeianus; also Rana catesbeiana after Yuan and others 2016) in concert with a bird and mammal study bias from largely diurnal collecting that occurred when California Red-legged Frogs were extant regionally. We found previously undocumented records for individuals of the genus Rana for Yosemite Valley, consistent with a dominant historical hydrology more compatible for Foothill Yellow-legged Frogs (Rana boylii), though none could be definitively identified as California Red-legged Frogs. We conclude that extensive anthropogenic impacts, including acute ecosystem alteration and American Bullfrog introduction, contributed to the failure to detect California Red-legged Frogs in many places regionally once amphibians became a research priority in the latter 20th century. The conservation translocation of California Red-legged Frogs to Yosemite Valley illustrates the integration of historical baselines with contemporary realities, allowing for the complexities of change over time rather than focusing on restoration to an imagined, ideal environment in the past.

Nonbreeding habitats are critically important for Rana draytonii, especially for individuals that breed in temporary bodies of water. We radiotracked 123 frogs to evaluate seasonal habitat use. Individual frogs were continuously tracked for up to 16 months. Some individuals remained at breeding ponds all year, but 66% of female and 25% of male frogs moved to nonbreeding areas, even when the breeding site retained water. Frogs at our main study site moved 150 m (median), roughly the distance to the nearest suitable nonbreeding area. The greatest straight-line distance traveled was 1.4 km, although the presumed distance traveled was 2.8 km. Females were more likely than males to move from permanent ponds (38% of females, 16% of males), but among dispersing frogs, males and females did not differ in distance moved. Some frogs left breeding sites shortly after oviposition (median  =  12 days for females, 42.5 days for males), but many individuals remained until the site was nearly dry. Fog provided moisture for dispersal or migration throughout the summer. Our data demonstrate that maintaining populations of pond-breeding amphibians requires that all essential habitat components be protected; these include (1) breeding habitat, (2) nonbreeding habitat, and (3) migration corridors. In addition, a buffer is needed around all three areas to ensure that outside activities do not degrade any of the three habitat components.

Populations forming the edge of a species range are often imperiled by isolation and low genetic diversity, with proximity to human population centers being a major determinant of edge stability in modern landscapes. Since the 1960s, the California red‐legged frog (Rana draytonii) has undergone extensive declines in heavily urbanized southern California, where the range edge has rapidly contracted northward while shifting its cardinal orientation to an east‐west trending axis. We studied the genetic structure and diversity of these frontline populations, tested for signatures of contemporary disturbance, specifically fire, and attempted to disentangle these signals from demographic events extending deeper into the past. Consistent with the genetic expectations of the ‘abundant‐center’ model, we found that diversity, admixture, and opportunity for random mating increases in populations sampled successively further away from the range boundary. Demographic simulations indicate that bottlenecks in peripheral isolates are associated with processes extending tens to a few hundred generations in the past, despite the demographic collapse of some due to recent fire‐flood events. While the effects of recent disturbance have left little genetic imprint on these populations, they likely contribute to an extinction debt that will lead to continued range contraction unless management intervenes to stall or reverse the process.