- Amy Lind - Tahoe and Plumas National Forests. Note: this person is no longer a Forest Service Research & Development employee.
- Conservation & River Regulation
- Ecology & Life History
- Citations (Abstracts)
- Regional Topics
- Map of R. boylii Distribution
- Additional Rana boylii Resources
Foothill Yellow-legged Frog (Rana boylii)
Wheeler, C.A., J.B. Bettaso, D.T. Ashton, and H.H. Welsh, Jr. 2014. [North Coast] Effects of water temperature on breeding phenology, growth and timing of metamorphosis of foothill yellow-legged frogs (Rana boylii): a case study of the regulated mainstem and unregulated tributaries of California's Trinity River. River Research and Applications: DOI: 10.1002/rra.2820.
Many riverine organisms are well adapted to seasonally dynamic environments, but extreme changes in flow and thermal regimes can threaten sustainability of their populations in regulated rivers. Altered thermal regimes may limit recruitment to populations by shifting the timing of breeding activities and affecting the growth and development of early life stages. Stream-dwelling anurans such as the foothill yellow-legged frog (Rana boylii) in the Trinity River of northern California are model subjects for examining associations between water temperature and the timing of oviposition, hatching, and metamorphosis, and body condition and size of tadpoles and metamorphs. Breeding activity, hatching success, and metamorphosis occurred later, and metamorphs were smaller and leaner along the regulated and colder mainstem relative to six unregulated tributaries of the Trinity River. Persistently depressed summer water temperatures appear to play a seminal role in inhibited tadpole growth on the regulated mainstem and may be a causative factor in the pronounced decline of this population. Environmental flow assessments should account for the influence of the thermal regime on the development of vulnerable embryonic and larval life stages to improve outcomes for declining amphibian populations.
Furey, P.C., S.J. Kupferberg, A.J. Lind. 2014. The perils of unpalatable periphyton: Didymosphenia and other mucilaginous stalked diatoms as food for tadpoles. Diatom Research 29: 267–280.
Proliferations of Didymosphenia geminata are becoming prevalent in rivers around the globe. In the Sierra Nevada of California, Didymosphenia and other taxa that produce mucopolysaccharide stalks (e.g., Gomphoneis, Cymbella) can dominate benthic environments, particularly in the altered hydrologic and thermal regimes downstream of dams. We compared the prevalence of stalked diatoms in paired reaches, one free-flowing and the other regulated, within two Sierran river systems, the American and Feather Rivers. In the regulated reaches, short-term power generation caused daily flow fluctuations and periphyton biovolume was dominated by either Didymosphenia (where hypolimnetic releases created cool summer temperatures) or other stalked diatom taxa (where temperatures were warm). Periphyton assemblages from the unregulated sites were significantly different from the regulated reaches based on biovolume, with Gomphonema being the genus at unregulated sites contributing to the dissimilarities after accounting for the stalked genera from the regulated reaches. We evaluated the consequences of mucopolysaccharides for a large-bodied grazer, tadpoles of the foothill yellow-legged frog (Rana boylii), in a factorial experiment manipulating diet and thermal regime. At 16.6?C mean daily temperature, tadpoles lost weight (72 h relative change of -16.1 ± 7.2%) when grazing on periphyton from a Didymosphenia-dominated site. At 19.9?C (similar to unregulated river conditions), tadpoles grazed Didymosphenia at a rate similar to tadpoles consuming higher protein control periphyton, but the former tadpoles did not grow (relative change of 4.3 ± 5.4% vs 30.7 ± 3.4% for control periphyton). When tadpoles were fed periphyton dominated by mucilaginous stalked diatoms other than Didymosphenia, tadpole weight loss was 21.0 ± 9.2% (cool) and 16.6 ± 5.6% (warm). The results illustrate that hydrologically or thermally mediated shifts in periphyton composition can have significant implications for the energy transferred to grazers.
Wheeler, C.A., J.B. Bettaso, D.T. Ashton, and H.H. Welsh, Jr. 2013. [North Coast] Effects of water temperature on breeding phenology, growth and timing of metamorphosis of foothill yellow-legged frogs (Rana boylii) on the mainstem and selected tributaries of California's Trinity River - 2004-2009. Report to the Trinity River Restoration Program. U.S. Forest Service, Redwood Sciences Laboratory and U.S. Fish and Wildlife Service.
Water temperatures in the Mainstem Trinity River during the late-spring and summer months have been substantially colder (10-20°C lower) since the construction of the dams compared to pre-dam conditions; water released into the Mainstem Trinity River from the bottom of the Trinity Reservoir is much cooler (hypolimnetic) than the surface water temperature (U.S. Fish and Wildlife Service and Hoopa Valley Tribe 2009). We predicted that frogs would be smaller at metamorphosis in the Mainstem and in colder water tributaries (i.e., higher elevation snow-influenced streams) since breeding likely occurs later and the colder water temperatures would impede growth and differentiation. The objectives of this study were to: 1) examine and compare key aspects of the reproductive cycle of yellow-legged frogs in different Trinity River tributaries, 2) examine and compare the phenology of reproduction, including rates of differentiation, time to metamorphosis, and size at metamorphosis, by tributary, and 3) to examine the differences as they relate to variation in water temperature regime, such that the influences of the hypolimnetic releases from the reservoir on the Mainstem Trinity could be contextualized and potentially mitigated.
Kupferberg, S.J., A. Catenazzi, and M.E. Power. 2013. [All Regions] The importance of water temperature and algal assemblage for frog conservation in northern California rivers with hydroelectric projects. Final Report. California Energy Commission, PIER. CEC-500 - TBD.
Multiple stressors, including altered flow regimes and habitat fragmentation associated with water storage and hydroelectric power generation, have contributed to the decline of foothill yellow-legged frogs (Rana boylii) in California. One potential mechanism contributing to decline is the effect of altered thermal conditions on development, and survival of early life stages. For 6 focal watersheds, each with known R. boylii populations in paired regulated and free-flowing river reaches, we measured thermal conditions from breeding through metamorphosis and determined that maximum average temperature during the warmest 30-day period (M30DAT) was a useful metric to characterize the period critical for successful maturation of tadpoles into frogs. By comparing sites occupied by frogs and cooler sites further upstream where frogs were sparse or absent, we found that the realized thermal niche for successful reproduction differs between the North / Central Coast and watersheds of the Sierra. When averaging observations from 2009 (warm, dry year) and 2010 (cooler, wetter) we observed that the realized thermal niche for tadpoles was approximately 2°C higher in the Sierra. At occupied sites, M30DAT during in the Sierra was 17.6-24.2°C, compared to 15.7-22.0°C in North and Central Coast rivers. The densest Sierran populations were in reaches where M30DAT >20°C. In laboratory experiments, tadpoles reared from eggs collected at Sierran sites exhibited a capacity for higher growth and faster development than those from coastal populations.
Experiments manipulating food resources along with temperature showed that thermal effects on tadpole digestion, growth, and survival were mediated through the quantity and quality (i.e. protein content) of algal food. We reared tadpoles in streams where M30DAT was colder, warmer, or within the range of temperatures documented at occupied sites in the 6 watersheds. Peak production of metamorphs (combined highest survival and largest size) occurred when M30DAT = 20-22°C and the diet was rich in diatoms from the genus Epithemia, which host cyanobacterial nitrogen fixing endosymbionts. We found that periphyton assemblages downstream of dams operated for peak power generation were not conducive to tadpole growth. When river discharge fluctuated daily, the flora was dominated by stalked diatoms (e.g. Didymosphenia geminata) that create copious extra-cellular mucus. Even at favorable temperatures, tadpoles did not grow on diets of mucilaginous stalked diatoms.
Conservation of R. boylii in rivers with hydroelectric power generation projects will depend on management that maintains sufficiently warm water during the breeding and tadpole rearing seasons. When alternative flow schedules are being evaluated, forecasts of changes in water temperature can be extended to predict consequences for frog populations. Managers will be able to assess the number of river kilometers downstream of dams that will be thermally suitable for frog reproduction.
Catenazzi, A., and S. J. Kupferberg. 2013. [All Regions] The importance of thermal conditions to recruitment success in stream-breeding frog populations distributed across a productivity gradient. Biological Conservation. Vol. 168, pp. 40-48.
Predicting the vulnerability of species to environmental change requires integrating observations of individual ecophysiological and behavioral responses with community level constraints. To assess the response of stream-breeding frogs (Rana boylii) to thermal stressors, such as cold water released from the depths of upstream reservoirs or warm water that results from climate change, we combined field manipulations with population censuses and environmental correlations. These frogs migrate between shaded tributaries and open canopy mainstem channels to oviposit where algal food is abundant for tadpoles. Within this context of spatial variation in aquatic primary productivity, we evaluated whether tadpole thermoregulatory behavior is a useful indicator of survival to metamorphosis and adult distribution. In a thermal gradient, tadpoles selected temperatures between 16.5-22.2°C (mean, 19.60 ± 0.6°C). We reared tadpoles in streams colder, warmer, or close to thermal preference. Temperature effects were mediated through algal quantity and quality. Mortality increased with increasing deviation from preferred temperatures, but the effects were ameliorated when tadpole diet was supplemented with algae (Cladophora glomerata with epiphytic nitrogen-rich diatoms, Epithemia spp.) harvested from sun-lit channels. Distribution of frogs in free-flowing and dammed reaches within a northern California watershed was in equilibrium with tadpole thermal preference. Populations were dense (>125 breeding females/km) where July water temperatures averaged 17.5-19°C in 2010, a relatively cool summer. Below 16°C, frogs were sparse with open canopy and absent under closed canopy. Integration of thermoregulatory behavior with ecological context can thus be useful to forecast recruitment when the thermal regimes of rivers are altered by anthropogenic factors.
Bondi, C.A., S.M. Yarnell, and A.J. Lind. 2013. [Sierra Nevada] Transferability of habitat suitability criteria for a stream breeding frog (Rana boylii) in the Sierra Nevada, California. Herpetological Conservation and Biology. Vol. 8, pp. 88-103.
Instream flow modeling is one tool historically used by resource managers to assess habitat suitability for aquatic species, including fish and benthic macroinvertebrates. Until recently, these methods had not been used for amphibians. Instream flow modeling requires quantitative habitat suitability criteria across a range of hydraulic conditions. We developed regional habitat suitability criteria (HSC) from data on habitat conditions at Foothill yellow-legged frogs (Rana boylii) oviposition and tadpole rearing locations in eight study sites in the northern Sierra Nevada mountains, California. We evaluated both univariate (percentile-based and interval-based) and multivariate logistic regression techniques for creating suitability criteria. The transferability and predictive performance of the HSC were evaluated using validation data gathered from other rivers in the Sierra Nevada and applying the criteria in a two-dimensional (2D) hydrodynamic model. We evaluated conditions under which predictive performance was poor to discern the limitations of each technique. Multivariate logistic regression analyses classified the majority of the river as low suitability, and consequently produced overestimates of suitable area for egg masses and underestimates of highly suitable area for tadpoles. Univariate HSC performed well on rivers that had similar geomorphology to the study rivers. For small rivers and creeks with shallow depths and finer substrates, locally-derived HSC are needed. The percentile based habitat suitability index (HSI) is recommended for regional habitat suitability criteria when the goal is to assess categorical levels of suitability. The interval-based HSI would be appropriate if further information on population outcomes (e.g., population trajectory, survival rates) could be quantitatively linked to fine scale gradients of suitability in hydraulic conditions. The univariate HSI are easily applied in 2D hydrodynamic models, which can provide information on oviposition and tadpole rearing conditions under various flow regimes. Managers can use HSC to make flow recommendations beneficial to R. boylii during the hydropower relicensing process.
Kupferberg, S.J., W.J. Palen, A.J. Lind, S. Bobzien, A. Catenazzi, J. Drennan, M.E. Power. 2012. [All Regions] Effects of flow regimes altered by dams on survival, population declines, and range-wide losses of California river-breeding frogs. Conservation Biology. Vol. 26, pp. 513-524.
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.
Yarnell, S.M., A.J. Lind, and J.F. Mount. 2012. Dynamic flow modelling of riverine amphibian habitat with application to regulated flow management. River Research and Applications. Vol. 28(2): 177-191. DOI: 10.1002/rra.1447
In regulated rivers, relicensing of hydropower projects can provide an opportunity to change flow regimes and reduce negative effects on sensitive aquatic biota. The volume of flow, timing and ramping rate of spring spills, and magnitude of aseasonal pulsed flows have potentially negative effects on the early life stages of amphibians, such as the Foothill yellow-legged frog (Rana boylii). Two-dimensional hydrodynamic modeling is one method to evaluate potential effects of flow variation on frog egg masses and tadpoles. We explored the usefulness of this technique by modeling habitat suitability under several pulsed flow scenarios in two river reaches in northern California, USA. We conducted analyses beyond simple weighted usable area calculations, such as quantifying the risk of scour or stranding, in order to quantify potential loss under different flow scenarios. The modeling results provided information on potential susceptibility to flow fluctuations as well as the influence of channel morphology on habitat suitability. Under each flow scenario, low percentages of suitable habitat remained suitable or were 'buffered' from the pulse, creating high potential for scour of egg masses or tadpoles. However, due to differences in channel morphologies, the wide, shallow study site provided 2-3 times the buffering capacity of the entrenched study site.
Additional analyses suggested that limited buffering capacity and lack of connectivity between suitable egg mass and tadpole habitats may explain why some hydraulically suitable habitats are unoccupied. This type of model-based analysis would be useful for managing foothill yellow-legged frogs or similar aquatic species in regulated river systems.
Yarnell, S, A. Lind, C. Bondi, R. Peek, and J. Mount. 2011. [Sierra Nevada] Validation of Regional habitat Suitability Criteria and Instream Flow Modeling Applications for the Foothill Yellow-Legged Frog (Rana boylii). Final Report. California Energy Commission, PIER.
In many current hydropower project relicensing studies, instream flow assessment methods are used to evaluate flow effects and proposed flow prescriptions on fish. These techniques may be applicable to other sensitive aquatic species, such as the riverine-breeding Foothill Yellow-legged frog (Rana boylii). Two major components of flow modeling were evaluated as part of this study. First, regional habitat suitability criteria (HSC) were developed using standard univariate and multivariate techniques and the predictive performance and transferability of different HSC methods were evaluated. Based on this evaluation, we recommend that separate creek and river HSC for the Sierra Nevada R. boylii be based on a percentile method. Second, three of the most commonly used instream flow assessment techniques: (1) one-dimensional habitat modeling, (2) two-dimensional hydrodynamic modeling, and (3) expert habitat mapping (judgment-based mapping by species experts), were evaluated. Several flow/habitat relationships were compared among the three modeling methods: total suitable habitat, effective habitat during flow recession, and gradients of suitability during a pulsed flow. Level of effort, scale of resolution, capacity for extrapolation, and specificity of modeling analyses were also qualitatively assessed. A comparison table is provided to aid resource managers in selecting the most appropriate habitat assessment method for R. boylii, given the specific conditions of a hydropower relicensing project. Finally, a website was constructed to provide an updated and publicly accessible synopsis of the status of knowledge on R. boylii, with particular focus on the effects of river regulation on this species. The website provides access to relevant data and literature, tabular summaries of ecology and risks, and a species locality map derived from multiple data sources. Collectively, the elements of the website offer a comprehensive update on the species and may help identify reference populations for monitoring and research.
Lind A.J., P.Q. Spinks, G.M. Fellers, and H.B. Shaffer. 2011. [All Regions] Rangewide phylogeography and landscape genetics of the Western US endemic frog Rana boylii (Ranidae): implications for the conservation of frogs and rivers. Conservation Genetics. 12(1): 269-284.
Genetic data are increasingly being used in conservation planning for declining species. We sampled both the ecological and distributional limits of the foothill yellow-legged frog, Rana boylii to characterize mitochondrial DNA (mtDNA) variation in this declining, riverine amphibian. We evaluated 1525 base pairs (bp) of cyto-chrome b and ND2 fragments for 77 individuals from 34 localities using phylogenetic and population genetic analyses. We constructed gene trees using maximum likelihood and Bayesian inference, and quantiﬁed genetic variance (using AMOVA and partial Mantel tests) within and among hydrologic regions and river basins. Several moderately supported, geographically-cohesive mtDNA clades were recovered for R. boylii. While genetic variation was low among populations in the largest, most inclusive clade, samples from localities at the edges of the geographic range demonstrated substantial genetic divergence from each other and from more central populations. Hydrologic regions and river basins, which represent likely dispersal corridors for R. boylii, accounted for signiﬁcant levels of genetic variation. These results suggest that both rivers and larger hydrologic and geographic regions should be used in conservation planning for R. boylii.
Kupferberg, S., Lind, A.J., V. Thill, and S.M. Yarnell. 2011. [All Regions] Water velocity tolerance in tadpoles of the foothill yellow-legged frog (Rana boylii): Swimming performance, growth, and survival. Copeia. No. 1, pp. 141-152.
We explored the effects of large magnitude flow fluctuations in rivers with dams, commonly referred to as pulsed flows,on tadpoles of the lotic-breeding Foothill Yellow-legged Frog, Rana boylii. We quantified the velocity conditions in habitats occupied by tadpoles and then conducted experiments to assess the tolerance to values at the upper limit of, and outside, the natural range. In laboratory flumes and field enclosures we mimicked the velocities observed during pulsed flows. In all experimental venues, the behavioral response of tadpoles was to seek refuge in the channel substrate when velocity increased. In a large laboratory flume, tadpoles moved freely at low water velocities (0–2 cm/s) and then sheltered among rocks when velocity increased. In a smaller scale laboratory flume, the median critical velocity was 20.1 cm/s. Critical velocity varied inversely with tadpole size, developmental stage, and proportion of time spent swimming. Velocities as low as 10 cm/s caused tadpoles approaching metamorphosis to be displaced. In field mesocosm experiments, tadpoles exposed to repeated sub-critical velocity stress (5–10 cm/s) grew significantly less and experienced greater predation than tadpoles reared at ambient velocities. Responses to velocity manipulations were consistent among tadpoles from geographically distinct populations representing the three identified clades within R. boylii. The velocities associated with negative effects in these trials are less than typical velocity increases in near shore habitats when recreational flows for white water boating or peaking releases for hydroelectric power generation occur.
Yarnell, S. M., Viers, J. H., and J. F. Mount. 2010. [Sierra Nevada] Ecology and Management of the Spring Snowmelt Recession. Bioscience. February. Vol. 60 (2) pp. 114-127.
We present a conceptual model for the ecology of the spring snowmelt recession based on the natural flow regime that relates the quantifiable components of magnitude, timing, and rate of change to abiotic and biotic factors that govern riverine processes. We find that shifts in the magnitude of the recession largely affect abiotic channel conditions, whereas shifts in the timing of the snowmelt primarily affect biotic conditions. Shifts in the rate of change affect both abiotic and biotic conditions, creating the largest observed changes to the stream ecosystem. We discuss these components with regard to the success of riverine species in California’s Mediterranean-montane environment. We then present two scenarios of change to the spring snowmelt recession—effects of flow regulation and climate warming—and discuss their potential implications for riverine ecology. Our conceptual model can help guide watershed stakeholders toward a better understanding of the impacts of changing spring recession conditions on stream ecosystems.
Gonsolin, T. E. 2010. [Central Coast] Ecology of foothill yellow-legged frogs in Upper Coyote Creek, Santa Clara County, CA. California State University, San Jose. Masters Thesis.
Visual encounter surveys, mark-recapture technique, and telemetry were used investigate breeding, movement, growth, habitat preferences, and predators of foothill yellow-legged frogs on Coyote Creek in Santa Clara County, California, from March 2004 to March 2006. The main stem and tributaries were intermittent in summer in all three years. Thermal conditions for breeding initiation were alike during 2004, 2005, and 2006. Breeding occurred in the main stem on descending limbs of the hydrograph. No breeding occurred in the middle main stem reach, which is ephemeral. Breeding occurred at less than an order of magnitude greater than base flows. Typically, larger females bred earlier, and egg mass size decreased as the breeding season progressed during 2004 and 2005. Males arrived earlier and remained in breeding areas longer. Resident tributary frogs moved greater distances than main stem frogs to breed. Females tended to travel farther than males and occupied habitats farther from the breeding areas. Frogs on Coyote Creek showed faster growth during their first year than Sierra Nevada and north Coast Range populations. Both sexes preferred pools and boulder-dominated habitat on both the main stem and tributary. Santa Cruz garter snakes were the most frequently encountered predator in the study area. However, all diurnal predators were scarce on the tributaries. Perennial water is a limiting factor within the study area, as illustrated by the movement patterns and timing of breeding.
Bursey, C., S. Goldberg, and J. Bettaso. 2010. [North Coast] Persistence and Stability of the Component Helminth Community of the Foothill Yellow-Legged Frog, Rana boylii (Ranidae), from Humboldt County, California, 1964-1965, Versus 2004-2007. The American Midland Naturalist, Vol. 163 (2) pp. 476-482.
Persistence and stability of the component helminth community of Rana boylii from Humboldt County, California was evaluated using two collections made 40 years apart (1964–1965 and 2004–2007). The component helminth community consisted of 13 species: one species of Cestoda (Distoichometra bufonis), six species of Digenea (Deropegus aspina, Glypthelmins quieta, Gorgoderina multilobata, Haematoloecus kernensis, Megalodiscus microphagus, echinostome metacercariae) four species of Nematoda, (Cosmocercoides variabilis, Hedruris sp., Rhabdias ranae, third stage Physalopterids) and two species of Acanthocephala (represented by centrorhynchid cystacanths and oligacanthorhynchid cystacanths). Twelve (92%) of the 13 species occurred in the 1964–1965 sample; nine (69%) of the 13 species were found in the 2004–2007 sample; eight (62%) of the 13 species occurred in both samples. Rana boylii isparasitized by generalist helminths that co-occur in other hosts. The aggregate of host species may be more important to parasite community stability than any single host species.
Bourque, R. 2008. [North Coast] Spatial Ecology of An Inland Population of The Foothill Yellow-Legged Frog (Rana boylii) in Tehama County, California. California State University, Humboldt. Masters Thesis, pp. 107.
Understanding the movements of anurans is important for developing successful conservation plans because breeding, foraging, and overwintering resources are often separated by time and space. Radio-telemetry was used to study the movements and habitat use of the Foothill Yellow-legged Frog (Rana boylii) in the Red Bank Creek watershed. Seventy-nine frogs (11 males and 68 females) inhabiting an inland watershed were opportunistically captured, fitted with radio-transmitters, and monitored during three two-month study periods. Females were tracked during one spring (2004) and two fall/winter seasons (2004 and 2005), while males were tracked during one spring season (2004). Site-specific weather conditions were monitored to evaluate associations with frog movement and habitat use. Movements and habitat use were highly variable among individuals during all study seasons. Frogs either centered activities at their initial capture locations or moved hundreds to thousands of meters among different stream habitats. The greatest distances traveled by male and female frogs were 0.65 km and 7.04 km, respectively. Frog size and age were independent of seasonal distances traveled. Mobile males and females moved 65.7 and 70.7 m/day (median), respectively, in spring and mobile females moved 37.1 m/day (median) in fall/winter. The maximum travel rate was 1386 m/day. Frogs used watercourses as movement corridors and rarely moved > 12 m from the stream channel. Spring movements were not associated with weather, but fall/winter movements were associated with increasing rain and humid conditions. Females showed an upstream directional bias during spring movements and a downstream bias for fall/winter movements. The results from this study highlight the need to manage R. boylii populations at the watershed scale to ensure protection of spatially separated resources commonly used by individuals throughout the year.
Corum, S. 2003. [North Coast] Effects of Sacramento Pikeminnow on Foothill Yellow-Legged Frogs in Coastal Streams. California State University, Humboldt. Masters Thesis, pp. 1-42.
An investigation of the effect of an introduced non-native fish species, Sacramento pikeminnow (Ptychocheilus grandis), on the native stream-dwelling frog Rana boylii, in coastal streams in northern California. Field surveys were used to compare frog densities in rivers with and without pikeminnow and tributaries with varying densities of pikeminnow. Although frog densities in rivers with pikeminnow were substantially lower in 2002, the frog densities of rivers with and without pikeminnow were comparable in 2003. The range of frog densities in the tributaries was similar to those in the rivers. In both the tributaries and rivers, there was a significant habitat effect on adult frog density (p<0.01), with most of the adult frogs in isolated pools and the least in the mainstem. In laboratory palatability trials, pikeminnow consumed recently hatched tadpoles, mid-development tadpoles, metamorphosed tadpoles, and adults, but not egg masses. In field experiments testing the effect of pikeminnow on the survival of the four palatable life stages, pikeminnow significantly reduced the survival of the mid-development tadpoles (p= 0.02), but none of the other stages. Different habitat requirements of the pikeminnow and frogs lead to limited overlap between the two species. Also, the most vulnerable stage to pikeminnow predation has relatively low reproductive value, the mid-development tadpole. This study suggests that, when considered alone, pikeminnow predation appears to have a limited effect on foothill yellow-legged frogs in the Eel River. However, pikeminnow predation along with other species introductions and habitat degradation may contribute to cumulative effects.
Davidson, C., H.B. Shaffer, M.R. Jennings. 2002. [Sierra Nevada] Pesticide Drift, Habitat Destruction, UV-B, and Climate-Change Hypotheses for California Amphibian. Conservation Biology. Vol. 16 (6), pp. 1588–1601.
Wind-borne pesticides have long been suggested as a cause of amphibian declines in areas without obvious habitat destruction. In California, the transport and deposition of pesticides from the agriculturally intensive Central Valley to the adjacent Sierra Nevada is well documented, and pesticides have been found in the bodies of Sierra frogs. Pesticides are therefore a plausible cause of declines, but to date no direct links have been found between pesticides and actual amphibian population declines. Using a geographic information system, we constructed maps of the spatial pattern of declines for eight declining California amphibian taxa, and compared the observed patterns of decline to those predicted by hypotheses of wind-borne pesticides, habitat destruction, ultraviolet radiation, and climate change. In four species, we found a strong positive association between declines and the amount of upwind agricultural land use, suggesting that wind-borne pesticides may be an important factor in declines. For two other species, declines were strongly associated with local urban and agricultural land use, consistent with the habitat-destruction hypothesis. The patterns of decline were not consistent with either the ultraviolet radiation or climate-change hypotheses for any of the species we examined.
Davidson, C., M.F. Bernard, and H.B. Shaffer. 2007. [All Regions] Effects of chytrid and carbaryl exposure on survival, growth and skin peptide defenses in foothill yellow-legged frogs. Environmental Science and Technology. Vol. 41, pp. 1771-1776.
Environmental contaminants and disease may synergistically contribute to amphibian population declines. Sub-lethal levels of contaminants can suppress amphibian immune defenses and, thereby, may facilitate disease outbreaks. We conducted laboratory experiments on newly metamorphosed foothill yellow-legged frogs (Rana boylii) to determine whether sublethal exposure to the pesticide carbaryl would increase susceptibility to the pathogenic chytrid fungus Batrachochytrium dendrobatidis that is widely associated with amphibian declines. We examined the effect of carbaryl alone, chytrid alone, and interactions of the two on individual survival, growth, and antimicrobial skin defenses. We found no effect of chytrid, carbaryl, or their interaction on survival. However, chytrid infection reduced growth by approximately one-half. This is the first report of suppressed growth in post-metamorphic amphibians due to infection with chytrid. Rana boylii skin peptides strongly inhibited chytrid growth in vitro, which may explain why chytrid exposure did not result in significant mortality. Skin peptide defenses were significantly reduced after exposure to carbaryl suggesting that pesticides may inhibit this innate immune defense and increase susceptibility to disease.
Dever, J. 2007. [North Coast] Fine-scale Genetic Structure in the Threatened Foothill Yellow-legged Frog (Rana boylii). Journal of Herpetology. Vol. 41 (1) pp. 168-173.
The Foothill Yellow-Legged Frog (Rana boylii) is a threatened river-dwelling amphibian endemic to California and Oregon. Determining the genetic structure of populations that have not yet declined is an important tool for their conservation. In this study, molecular markers were used to assess the genetic structure of R. boylii. The ND2 region of the mitochondrial genome and Random Amplified Polymorphic DNA (RAPD) markers were examined amongst 51 individuals collected from seven relatively pristine tributaries branching off the Eel River in Northern California. Both markers exhibited significant genetic differentiation among tributaries; however, the RAPD markers revealed a positive correlation between geographic distance and genetic distance. Cluster analysis illustrated a distinct separation between northern and southern tributaries within the study site. In contrast, relatively little geographic structure was apparent when mtDNA haplotypes were examined. Discordance may be caused by the number of loci examined in the mitochondrial and nuclear genomes, recent divergence, and sex-biased dispersal.
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Fox, W. 1952. Notes on the feeding habits of Pacific coast garter snakes. Herpetologica 8:4-8.
Fuller, T.E. 2008. [North Coast] The Spatial Ecology of The Exotic Bullfrog (Rana catesbeiana) and its Relationship to the Distribution of the Native Herpetofauna in a Managed River System. California State University, Humboldt., pp. 1-65.
Prior to western settlement, the Trinity River probably offered little suitable habitat for bullfrogs (Rana catesbieana). Anthropogenic habitat modifications such as mining and homesteading may have resulted in conditions more favorable for bullfrogs. Damming in 1963 led to modifications in riverine habitat, producing a highly modified lotic system which is much different from pre-dam conditions. Research has shown these habitat modifications to negatively impact foothill yellow-legged frogs (Rana boylii). My objectives were to determine the downstream distribution of an exotic ranid frog, the bullfrog, and its relationship to the foothill yellow-legged frog, other native amphibians, and the habitats they occupy along the regulated Trinity River. I used census data from 2004 to determine bullfrog occupancy and data on breeding from 2005 to determine bullfrog-breeding habitat on the Trinity River. With the occupancy data, I also examined native species composition in relation to bullfrog habitats and plotted bullfrog and native species distribution along the river. Bullfrog occupancy models were developed for both spring/summer high-flow and late summer low-flow surveys, with the low-flow model producing more accurate information than the high-flow model. Top predictor variables for all occupancy models were: max depth, percentage rooted floating vegetation, and river mile, although individual variables showed some variation in significance between the two flow regimes. The breeding model was more stable and out-performed the bullfrog occupancy models. The breeding model had high predictability and was positively correlated with the variables: percentage lentic, percentage rooted floating vegetation, max depth and river mile. Canopy cover was negatively correlated and water clarity had no relationship to bullfrog breeding sites. Most sites where bullfrogs were found also provided habitat for western pond turtles and western toads. Additionally, rough-skinned newts were commonly found at bullfrog breeding sites. Using the occupancy data set, native species and bullfrog distributions were inversely correlated along the 43-mile river reach below the dam. My results suggested that if one wished to control bullfrog populations on the Trinity River the most successful approach would be to focus management efforts on bullfrog breeding sites. Over half of the bullfrog breeding sites were artifacts of historic mining activities, whereas other breeding sites are a result of dam-induced habitat modifications. Making restoration of those sites a high priority could greatly benefit native species.
Fuller, D. D., and A. J. Lind. 1992. [North Coast] Implications of fish habitat improvement structures for other stream vertebrates. In: R. Harris and D. C. Erman (eds.), Proceedings of the Symposium on Biodiversity of Northwestern California. Pp. 96-104. Santa Rosa, California.
Lack of rearing habitat for stream-dwelling juvenile steelhead (Oncorhynchus mykiss) during summer low-flow conditions is considered to be the primary factor limiting these populations in the Pacific Northwest. Fishery managers have commonly focused on changing low-complexity stream reaches into habitat more favorable to juvenile steelhead through installation of instream structures, such as deflectors. Instream structures that improve habitat for target fish species may alter habitat required by other vertebrates in stream ecosystems. Foothill yellow-legged frog (Rana boylii) eggs and tadpoles are reared in shallow stream margins, which often occur adjacent to low gradient riffles in alluvial stream reaches.
We present observations on the effects of placement of instream boulder deflectors on physical habitat, juvenile steelhead, foothill yellow-legged frogs, and western aquatic garter snakes (Thamnophis atratus) in one 30 m reach of Hurdygurdy Creek (Del Norte County, California). We also examined habitat associations of foothill yellow-legged frog egg masses throughout the lower 5 km of the creek. Steelhead utilization of instream structures was found to vary depending on season and streamflow. Foothill yellow-legged frogs utilized the 30 m reach for breeding during the three years prior to the deflector placement, but not during the three years following placement. The diet of the western aquatic garter snake appeared to differ after placement of structures. Though these shifts indicate that predators are somewhat flexible, the potential effects of changes in prey availability for the whole stream community are unknown. We recommend consideration of all members of the aquatic community in stream habitat management.
Garcia and Associates (GANDA). 2008. [Sierra Nevada] Identifying Microclimatic and Water Flow Triggers Associated with Breeding Activities of a Foothill Yellow-Legged Frog (Rana boylii) Population on the North Fork Feather River, California. California Energy Commission, PIER Energy Related Environmental Research Program. CEC-500-2007-041
Using visual surveys and radio telemetry, researchers monitored movements and breeding activities of a population of foothill yellow-legged frogs (Rana boylii) to determine their relationship to climatic variables in six tributaries and their associated breeding sites on the Poe and Cresta reaches of the North Fork Feather River (NFFR) during spring in 2004 and 2005. Male frogs left tributaries earlier than females and stayed longer at breeding sites. Breeding areas were located along the mainstem river adjacent to the tributaries, and the frogs lived around the tributaries for most of the year. Time of year was the only parameter statistically correlated with initial movements in females. In late April/early May, when mean daily tributary temperatures were ≥ 10°C (≥ 50°F), females left home ranges on tributaries to breed on the NFFR. Most of the frog laid eggs when mean mainstem temperatures were between 10°C (≥ 50°F) and 16°C (≥ 61°F), and mainstem flow was between baseflow and less than 55 percent above baseflow. Length of stay by females at river breeding sites was extended by high flows and, on the Cresta Reach, relatively low numbers of males. Late season rains and associated high flows delayed breeding in 2005. Based on the model of environmental parameters affecting breeding activity, this study provides hydroelectric power managers information (such as movement dates, temperature, and flow preferences) to enhance foothill yellow-legged frog breeding success by preventing sharp fluctuations in the water levels during the breeding season from April through June.
Haggarty, M. 2006. [North Coast] Habitat differentiation and resource use among different age classes of post metamorphic Rana boylii on Red Bank Creek, Tehama County, California. California State University, Humboldt. Masters Thesis.
To obtain the most complete understanding of a species’ life history requirements, one must know what habitat characteristics and resources are critical to each life history stage. Rana boylii are known to associate with various stream habitats throughout their life cycle, and these habitat associations may vary based on changes in age, season or both. In this study I looked at meso-scale habitat use and resource use among adult, sub- adult, and metamorph R. boylii on Red Bank Creek, Tehama County, California during three seasons using visual encounter surveys. For each age class the proportion of habitat used was compared to the proportion of habitat available to see if habitat selection existed. The proportions of each age class observed in each of the four habitat types over time were also compared, to determine if habitat differentiation existed between age classes or seasonally. The results indicated that adults and sub-adults generally used different habitat than metamorphs, but metamorph habitat use changed seasonally. Adults and sub-adults showed a preference for pool and riffle habitat, whereas young of the year metamorphs selected for slower moving glides and runs. However, after metamorphs had overwintered they selected for riffles. These results suggest R. boylii exhibit natal site fidelity. Diet data were obtained using a procedure known as gastric lavage. The results of the diet analysis indicated that all age classes of R. boylii consume terrestrial insects. There were no significant differences in the taxonomic groups of insects found in the diet samples of different age classes. There was also no significant difference in mean prey size for different age classes. However, the results suggest that R. boylii are gape limited predators, since larger frogs consumed a greater proportion of large prey items. This lack of a significant result could be due to sample size.
Hayes, M. P. and M. R. Jennings. 1988. Habitat correlates of the distribution of California red-legged frog (Rana aurora draytonii) and Foothill yellow-legged frog (Rana boyii): implications for management. In: R.C. Szaro, K.E. Severson, D.R. Patton, tech. cords. Management of Amphibian, Reptiles, and Small Mammals in the North America. pp. 144-158. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Gen. Tech. Rep. RM-166, Fort Collins, Colorado.
Hothem, R.L., M.R. Jennings, and J.J. Crayon. 2009. [Central Coast] Mercury contamination in three species of anuran amphibians from the Cache Creek Watershed, California, USA. Environmental Monitoring and Assessment, April, pp. 1-16.
Fish and wildlife may bioaccumulate mercury (Hg) to levels that adversely affect reproduction, growth, and survival. Sources of Hg within the Cache Creek Watershed in northern California have been identiﬁed, and concentrations of Hg in invertebrates and ﬁsh have been documented. However, bioaccumulation of Hg by amphibians has not been evaluated. In this study, adult and juvenile American bullfrogs (Lithobates catesbeianus) and foothill yellow-legged frogs (Rana boylii), adult Northern Paciﬁc treefrogs (Pseudacris regilla), and larval bullfrogs were collected and analyzed for total Hg. One or more species of amphibians from 40% of the 35 sites had mean Hg concentrations greater than the US Environmental Protection Agency’s tissue residue criterion for ﬁsh (0.3 μg/g). Of the bullfrog tissues analyzed, the liver had the highest concentrations of both total Hg and methyl mercury. Total Hg in carcasses of bullfrogs was highly correlated with total Hg in leg muscle, the tissue most often consumed by humans.
Kupferberg, S. 1996. [North Coast] Hydrologic and geomorphic factors affecting conservation of a river-breeding frog (Rana boylii). Ecological Applications. Vol. 6 (4), pp. 1332-1344.
Organisms that live in highly variable environments, such as rivers, rely on adaptations to withstand and recover from disturbance. These adaptations include behavioral traits, such as habitat preference and plasticity of reproductive timing, that minimize the effects of discharge fluctuation. Studies linking hydrologic regime, habitat preference, and population processes, however, are predominantly limited to fish. Information on other sensitive taxa is necessary to facilitate conservation of multispecies assemblages and restoration of biodiversity in degraded river channels. I studied the functional relationship between physical habitat and reproduction of the foothill yellow-legged frog (Rana boylii), a California State Species of Special Concern. From 1992 to 1994, I mapped breeding sites along 5.3 km of the South Fork Eel River in northern California and monitored egg survival to hatching. Frogs selected sites over a range of spatial scales and timed their egg-laying to avoid fluctuations in river stage and current velocity associated with changes in discharge. The main sources of mortality were desiccation and subsequent predation of eggs in a dry year and scour from substrate in wet years, both caused by changes in stage and velocity. At the finest spatial scale, frogs attached eggs to cobbles and boulders at lower than ambient flow velocities. At larger scales, breeding sites were near confluences of tributary drainages and were located in wide shallow reaches. Clutches laid in relatively narrower and deeper channels had poor survival in rainy as well as dry springs. Most breeding sites were used repeatedly, despite between- and within-year variation in spring stage of the river. This pattern of site selection suggests that conservation of Rana boylii may be enhanced by maintaining or restoring channels with shapes that provide stable habitat over a range of river stages.
Kupferberg, S. 1997. [North Coast] Bullfrog (Rana catesbeiana) invasion of a California river: The role of larval competition. Ecology. Vol. 78 (6) pp. 1736-1751.
Kupferberg studied the invasion of Rana catesbeiana (the bullfrog) into a northern California river system where bullfrogs are not native. Native yellow-legged frogs, Rana boylii, a species of special concern, were almost an order of magnitude less abundant in reaches where bullfrogs were well established. Kupferberg assessed the potential role of larval competition in contributing to this displacement in a series of field manipulations of tadpole density and species composition. The impact of R. catesbeiana on native tadpoles in the natural community agreed with the outcome of more artificial experiments testing pairwise and three-way interactions. In 2-m2 enclosures with ambient densities of tadpoles and natural river biota, bullfrog tadpoles caused a 48% reduction in metamorph size, and no significant effect on survivorship. Bullfrog tadpoles significantly affected benthic algae, although effects varied across sites. Responses to bullfrogs in field settings were similar qualitatively to results seen in smaller-scale experiments designed to study size-structured competition among disparate age/size classes of species pairs and trios. Competition from large over-wintering bullfrog larvae significantly decreased survivorship and growth of native tadpoles. Competition from recently hatched bullfrog larvae also decreased survivorship of R. boylii and H. regilla. Native species competed weakly, both interspecifically and intraspecifically. The only suggestion of a negative impact of a native species on bullfrogs was a weak effect of H. regilla on recent hatchlings. Competition appeared to be mediated by algal resources, and there was no evidence for behavioral or chemical interference. These results indicate that, through larval interactions, bullfrogs can exert differential effects on native frogs and perturb aquatic community structure.
Kupferberg, S., Catenazzi, A., Lunde, K., Lind, A., and Palen, W. 2009a. [North Coast] Parasitic copepod (Lernaea cyprinacea) outbreaks in Foothill Yellow-legged Frogs (Rana boylii) linked to unusually warm summers and amphibian malformations in Northern California. Copeia. No. 3, pp. 529-537.
How climate change may affect parasite–host assemblages and emerging infectious diseases is an important question in amphibian decline research. We present data supporting a link between periods of unusually warm summer water temperatures during 2006 and 2008 in a northern California river, outbreaks of the parasitic copepod Lernaea cyprinacea, and malformations in tadpoles and young of the year Foothill Yellow-legged Frogs (Rana boylii). Relative to baseline data gathered since 1989, both 2006 and 2008 had significantly longer periods when daily mean water temperatures exceeded 20˚C compared to years without copepod outbreaks. Infestation varied spatially in the watershed, as prevalence increased concomitantly with temperature along a 5.2 km longitudinal transect. At breeding sites of R. boylii with copepods in 2006, infestation ranged from 2.9% of individuals upstream to 58.3% downstream. In 2008, copepods were absent from the most upstream sites and infested up to 28.6% of individuals sampled at downstream locations. Copepods most frequently embedded near a hind limb or the cloaca. Among individuals with parasites in 2006, 26.5% had morphological abnormalities compared to 1.1% of un-infested individuals. In 2008 when the infestation peak occurred late in development (post Gosner stage 39), abnormalities were not associated with copepod infestation. In both years, recently metamorphosed frogs with copepods were, on average, slightly smaller than those not infested. These occurrences represent a sudden increase in local prevalence atypical for this river ecosystem. Previously we had only once seen copepods on amphibians (on non-native Bullfrogs, Rana catesbeiana), six km further downstream. Pacific Chorus Frogs, Pseudacris regilla, which co-occur with R. boylii in shallow near shore habitats, were not used as hosts. The data suggest that increasing summer water temperatures, decreased daily discharge, or a combination of both, promote outbreaks of this non-native parasite on an indigenous host, and could present a threat to the long-term conservation of R. boylii under the flow regime scenarios predicted by climate change models.
Kupferberg, S., Lind, A.J., and Palen, W. J. 2009b. [All Regions] Pulsed Flow Effects on The Foothill Yellow-Legged Frog (Rana boylii): Population Modeling. Final Report. California Energy Commission. pp. 1-92.
The decline of the river breeding foothill yellow-legged frog (Rana boylii) has been attributed to the altered flow regimes and habitat fragmentation associated with water storage and hydropower dams. Recent research has provided insight into potential mechanisms for these declines, confirming that early life history stages (embryos and tadpoles) are negatively affected by altered hydrology, especially pulses in water flows during spring and summer which change water velocities and depths in oviposition and rearing habitats. To evaluate whether such early life stage impacts could ultimately affect R. boylii population dynamics, we developed a 30-year stochastic matrix population model (Reference model) and explored a range of possible hydrologic and demographic perturbations to these virtual populations. While most female R. boylii appear to reach maturity at age 3, there is evidence that some Central Coast populations may reach maturity at age 2. To account for this potential regional life-history difference, we also developed a “two year to maturity” reference model, and explored a subset of relevant hydrologic scenarios. For each reference model, R. boylii life-stage specific survival rates were collected by new field efforts and assembled from existing data provided by other researchers and the literature for populations in hydrologically un-regulated rivers. To incorporate variability and uncertainty in these rates, distributions of possible values for each vital rate were described based on multiple data sources, and these distributions served as the basis for stochastic projections. Thirty different perturbations to the reference models were evaluated, with each scenario based on expected effects of altered hydrology for single or multiple life stages. The 30-year probability of extinction increased substantially (relative to the reference models) with small starting population sizes and in scenarios with high levels of stranding and/or scoring of egg masses or tadpoles. Multivariate sensitivity analysis confirms that egg mass scouring, and tadpole, juvenile, and adult survival are key factors influencing overall population dynamics. Modeled populations were unable to persist with multiple artificial pulsed summer flows or combinations of hydrologic stressors suggesting that the fate of early life stages can be critical to R. boylii population persistence in hydrologically altered rivers. A key observation stemming from this modeling effort is the need for better demographic data collection for R. boylii, especially annual tadpole and juvenile survival, and a functional understanding of how specific changes in hydrology affect particular life stage survival rates. Until such data are collected and incorporated into a similar modeling effort, the results reported here should be interpreted as preliminary and predictions made about real R. boylii populations under altered hydrologies will remain highly uncertain.
Kupferberg, S., Lind, A., Mount, J., and Yarnell, S. 2009c. [Sierra Nevada] Pulsed Flow Effects on the Foothill Yellow-Legged Frog (Rana boylii): Integration of Empirical, Experimental, and Hydrodynamic Modeling Approaches. Final Report. California Energy Commission, PIER.
Four analytical approaches support the hypothesis that altered flow regimes, particularly spring and pulsed discharges, contribute to the decline of foothill yellow-legged frogs Rana boylii in regulated rivers. (1) A review of literature and FERC re-licensing reports indicates that egg masses are negatively affected by pulsed flows via scouring, or desiccation, if spawning occurs during spills that abruptly cease. Tadpole stranding was documented in several studies. Effects on young of the year and older life stages were equivocal. (2) Long-term population monitoring in three watersheds shows that frequency and magnitude of pulsed flows that harm embryos and tadpoles are factors in determining adult population status. These effects are offset by 2-3 years, representing the time to reproductive maturity in central and northern California. (3) Experiments illustrate that tadpoles seek refuge in the substrate as velocity increases, are not adapted for sustained swimming, and are swept downstream. Tadpoles confined to refugia face predation and energetic costs in terms of growth and development. (4) Simulations using River2D, a 2-dimensional hydrodynamic model, show that velocity and depth conditions exceed tolerances of R. boylii egg masses and tadpoles during a range of pulsed flows. While mesoscale suitability of near shore habitat was accurately predicted, error in modeled point velocities at egg locations arose from limitations in fine scale surveying of the large, poorly sorted, rock substrate. Management that avoids aseasonal flow fluctuations would benefit R. boylii, and other taxa, whose lifecycles are synchronous with the natural timing of runoff in California’s rivers.
Leidy, R.A., E. Gonsolin, and G.A. Leidy. 2009. [Central Coast] Late-Summer Aggregation of the Foothill Yellow-Legged Frog (Rana boylii) in Central California. The Southwestern Naturalist. Vol. 54 (3).
We report on a late-summer, above-ground aggregation of foothill yellow-legged frogs (Rana boylii) in the Diablo Range, Santa Clara County, California. Our observation provides the first published account of aggregation in this species.
Lind, A. 2003. [Sierra Nevada] The Distribution and Habitat of Foothill Yellow-legged Frogs (Rana boylii) on National Forests in Southern Sierra Nevada Mountains of California. Report to the FHR Program of Region 5 of the USDA Forest Service. pp. 1-31.
Since 1990, foothill yellow-legged frogs have been observed at 24 localities (= populations) on the three Southern Sierra Nevada National Forests; 21 on the Stanislaus, one on the Sierra, and two on the Sequoia. These are considered to be currently extant populations. Twenty of the 24 populations are located on “unimpaired” streams (no dams or major diversions) with varying levels of other management activities (e.g. roads and recreation). A better understanding of the habitat requirements for these populations is needed to help set habitat conditions and water management criteria for hydropower facilities during re-licensing efforts as well as for other activities which can affect riparian and aquatic environments. This report documents the distribution and habitat conditions for foothill yellow-legged frogs on three southern Sierra Nevada National Forests. Detailed data from three populations on the Sierra and Stanislaus National Forests provide additional information on relative abundance and habitat associations for these populations. Egg masses and larvae have received somewhat more attention here because of the known sensitivities of these life stages from studies in other part’s of this frog’s geographic range. The report is organized into three major sections: distribution, relative abundance from recent surveys, and habitat associations. Within each section, results are presented separately for each National Forest. Photographs are used to delineate section breaks throughout the report.
Lind, A. 2005. [All Regions] Reintroduction of a Declining Amphibian: Determining an Ecologically Feasible Approach for the Foothill Yellow-legged Frog (Rana boylii) Through Analysis of Decline Factors, Genetic Structure, and Habitat Associations. UC Davis. Dissertation.
Species reintroductions provide a model for integrating practical and theoretical aspects of conservation biology. However, we currently lack a clear understanding of the factors that determine the outcome of reintroduction programs for many taxa. Combining pre-reintroduction research on ecology, genetics, and causative factors of declines with experimental reintroductions and rigorous monitoring, offers an approach that should increase reintroduction success rates. Amphibians present challenges as reintroduction subjects due to characteristics such as biphasic life cycles, low mobility, and patchy distributions. This study focused on a stream-dwelling, declining amphibian in California and Oregon, the foothill yellow-legged frog (Rana boylii), and included three components: (1) determining primary causes of decline, (2) describing range-wide genetic variation, and (3) quantifying habitat associations. For decline factors, the analysis approach was to spatially relate the current status of R. boylii (present or absent) at historic localities to: geographic characteristics, land uses, wind-borne toxins, climatic variables, and proximity and size of dams. Climatic variables showed strong influence in multivariate models. There was also evidence for interactions, especially that negative effects of dams appeared to be exacerbated in areas with low precipitation. For genetic analyses, 1525 total base pairs from sequences of two mtDNA fragments (Cytochrome B and ND2) for 77 individuals from 34 localities were used. Phylogenetic analyses recovered several well-supported, geographically congruent clades within R. boylii. Genetic variation was low among populations in the largest, most inclusive clade, but individuals from several localities showed substantial divergence. Hydrologic regions, which represent likely dispersal corridors for R. boylii, show promise in explaining patterns of genetic variation. The habitat associations component focused on microhabitat scale oviposition site selection coupled with larger scale evaluations of occurrence and relative abundance at breeding areas. Oviposition microhabitat characteristics such as water depth, water velocity, and stream substrate showed narrow ranges among study localities. These results suggest that habitat selection results in population stability for R. boylii even within the substantial temporal and spatial variability of stream environments. I discuss the application of these results to potential reintroductions of R. boylii and propose a conceptual model for integrating this and other information into reintroduction programs.
Lind, A.J., and H.H. Welsh Jr. 1994. [North Coast] Ontogenetic changes in foraging behavior and habitat use by the Oregon garter snake, Thamnophis atratus hydrophilus. Animal Behaviour. Vol. 48: 1261-1273.
Foraging behavior, stream habitat use and food habits of a population of the aquatic, Oregon garter snake were studied in the field during the spring and summer of 1987 and 1988. Continuous records of behavior and habitat use were obtained for each snake. Adults foraged more actively and in a wider variety of stream habitats than juveniles or neonates. Adults also fed on a wider variety of prey types and sizes, especially concentrating on large, Pacific giant salamander, Dicamptodon tenebrosis, larvae and neotenes, in the mid-stream substrates. Juvenile and neonate snakes fed on relatively smaller prey that inhabited shallow stream margins. Consumption of relatively large prey by adults and smaller prey by juveniles indicated a shift in foraging ‘strategy’ from frequent feeding on small prey to infrequent feeding on large prey. These ontogenetic changes in foraging behavior, habitat use and food habits of Oregon garter snakes are probably the result of a combination of proximate ecological, morphological and physiological constraints. Ultimately, these behavioral shifts may have a phylogenetic origin that reflects the strong advantage of single large meals versus many small meals for many modern snake lineages.
Lind, A.J., H.H. Welsh Jr., and R.A. Wilson. 1996. [North Coast] The effects of a dam on breeding habitat and egg survival of the foothill yellow-legged frog (Rana boylii) in Northwestern California. Herpetological Review. Vol. 27 (2).
Dams and water diversion projects have been proposed as causes of declines of many native frogs, but the effects of these projects have not been quantitatively evaluated. Our study provides information on both direct and indirect effects of a dam on the foothill yellow-legged frog (Rana boylii) in a northwestern California river system. Our objectives were: (1) to describe the changes in Rana boylii breeding habitat in a dammed river prior to and some years following dam construction, and (2) to document the effects of the timing of water releases from the dam on the reproductive ecology of this population. Our study took place on the Trinity River in Trinity County, California. On the Trinity River, two aspects of the dams are having significant impacts on the Rana boylii population. First, river morphology has changed significantly since flows became controlled in 1963, and as a result a significant amount of breeding habitat has been lost. Data from a comparably-sized undammed river fork in the same system (the South Fork Trinity) demonstrated that both the number of potential sites and the total number of egg masses were substantially higher on this fork than in our main stem study area. The second factor is the timing of high-flow releases from the dam. In at least two of the last four years, entire cohorts of Rana boylii were lost along our main stem study reach because of unseasonal high flow releases. We believe the negative impacts we have identified on the mainstem Trinity River can be reduced with thoughtful management. Habitat loss is a critical problem and Rana boylii has responded to "bank feathering" restoration projects within one year of construction. Ten of the 24 egg masses found in 1994 surveys were at restoration sites. However, we do not know whether frogs using these newly created habitats are additions to the breeding population or whether the frogs have moved into these areas simply because they are more suitable than what is currently available on the river.
Lind, A. and S. Yarnell. 2008. [All Regions] Habitat Suitability Criteria For The Foothill Yellow-legged Frog (Rana boylii) in the Northern Sierra Nevada and Coast Ranges of California. Foothill Yellow-Legged Frog Habitat Suitability Criteria Technical Work Group. Prepared for PG&E.
The condition and suitability of key habitat elements is one component of status assessments for species at risk. The foothill yellow-legged frog (Rana boylii) inhabits a variety of lotic ecosystems, many of which have undergone substantial alteration of hydrologic regimes as a result of water storage, diversion, and hydroelectric power generation projects. Because of its declining status, R. boylii has become a focal species in recent Federal Energy Regulatory Commission (FERC) re-licensings of hydroelectric projects. In addition to direct population monitoring, habitat assessments and instream flow modeling are being conducted for R. boylii and other aquatic species during FERC re-licensings in California. We reviewed 31 pre-existing habitat use datasets for R. boylii from 15 rivers in the Sierra Nevada and Coast Ranges of California. Five rivers (four Sierran, one Coast Range) had robust datasets for key habitat variables. Using this data, we developed suitability criteria for three aquatic habitat variables (water depth, water velocity, and substrate) for pre-metamorphic life stages (egg masses and tadpoles) of R. boylii. We focused on egg masses and tadpoles because of the ample existing data and because effects of changes in hydrologic regimes and river habitats were thought to be more severe for these highly aquatic life stages. Three suitability levels (suitable, marginally suitable, and not suitable) were defined for each life stage and habitat variable. These levels were based on the range of water depth, water velocity, and substrate values observed for 90%, 10%, and 0% of egg masses or tadpole groups. Consistent with previous natural history accounts and studies, shallow water, slow water velocity, and large substrates represented the highest suitability. These criteria will ultimately be used in a 2-dimensional hydrodynamic model to determine habitat suitability at a variety of water flow release levels for particular river reaches. Remaining information gaps are validation of the criteria in other rivers and exploration of the development of similar criteria for post-metamorphic life stages.
Macey, J.R., J.L. Strasburg, J.A. Brisson, V.T. Vredenburg, M. Jennings, and A. Larson. 2001. [All Regions] Molecular Phylogenetics of Western North American Frogs of the Rana boylii Species Group. Molecular Phylogenetics and Evolution. Vol. 19 (1), pp. 131–143.
Phylogenetic relationships among frogs of the genus Rana from western North America are investi-
gated using 2013 aligned bases of mitochondrial DNA sequence from the genes encoding ND1 (sub-
unit one of NADH dehydrogenase), tRNA Ile, tRNA Gln, tRNA Met, ND2, tRNA Trp, tRNA Ala, tRNA Asn , tRNA Cys, tRNA Tyr, and COI (subunit I of cytochrome c oxidase), plus the origin for light-strand replication (OL) between the tRNA Asn and tRNA Cys genes. The aligned sequences contain 401 phylogenetically informative characters. A well-resolved phylogenetic hypothesis in which the Rana boylii species group (R. aurora, R. boylii, R. cascadae, R. muscosa, and R. pretiosa) is monophyletic is obtained. Molecular sequence divergence suggests that the R. boylii species group is approximately 8 million years old. The traditional hypothesis showing monophyly of the yellow-legged frogs (R. boylii and R. muscosa) is statistically rejected in favor of a hypothesis in which R. aurora, R. cascadae, and R. muscosa form a clade. Re-analyses of published nuclear ribosomal DNA restriction-site data and allozymic data support a monophyletic R. boylii group, but do not effectively resolve relationships among species within this group.
MacTague, L. and P.T. Northern. 1993. [North Coast] Underwater Vocalization by the Foothill Yellow-Legged Frog (Rana boylii). Transactions of the Western Section of the Wildlife Society. Vol. 29, pp. 1-7.
The foothill yellow-legged frog (Rana boylii) is a Species of Special Concern in California and a Category 2 candidate for Federal Listing. In April and May of 1991, in and along Santa Rosa Creek, Sonoma County, we used an aerial microphone and a hydrophone to obtain recordings of its vocalizations. Except for faint aerial calls given while a frog was clasped about the pectoral girdle by an investigator, the sounds were produced while the frogs were completely immersed in water. Representative tape recordings were analyzed by computer using the MacSpeech Lab II program. Five different vocalizations were identified: a short, unpulsed call; a short, pulsed call given when frogs were clasped by the investigator; pulsed calls of two intermediate lengths; and a long call in which groups of pulses are clustered into notes. The extensive vocabulary of the frog suggests that it may use vocalizations for a number of behavioral functions, such as advertisement of territory, vocal defense of territory, and attraction of mates. This previously-unreported phenomenon of underwater vocalization by R. boylii has at least three implications for management: (1) hydrophones could potentially be used in field censuses to enhance the detection abilities of surveyors during the breeding season; (2) phonic aspects of the phenotype should be used in conjunction with molecular, morphometric, and other traits in studies of geographic variation; and (3) habitat analyses should be done with an awareness that calling males may have requirements that differ from those of egg-laying females.
Moyle, P. 1973. [Sierra Nevada] Effects of Introduced Bullfrogs, Rana catesbeiana, on the Native Frogs of the San Joaquin Valley, California. Copeia. Vol. 1973 (1) pp. 18-22.
Rana catesbeiana was introduced into California between 1914 and 1920 and has since spread throughout the state. In the San Joaquin Valley it has become the dominant frog on the valley floor and has spread into the Sierra Nevada foothills. It is most abundant in the warm low elevation pools of the foothill streams, in areas heavily altered by man, although at least two populations are established above 1600 m elevation. Of the two frog species native to this region, R. aurora is either absent or very rare at the present time, while R. boylii is found mostly in small permanent foothill streams higher than 200 m elevation, in areas not occupied by R. catesbeiana. The disappearance of R. aurora from the region, and the continuing reduction in range of R. boylii, is attributed to habitat alteration coupled with predation and competition from R. catesbeiana.
Norman, B.R. and M. Mollier. 2002. [North Coast] Concerning an Albino Foothill Yellow-Legged Frog (Rana boylii, Amphibia, Anura, Ranidae), from Red Cap Drainage, Humboldt County, California. Bulletin of Chicago Herpetological Society. Vol. 37 (1) pp. 2-3.
One recently transformed, fully albino foothill yellow-legged frog, Rana boylii, was discovered in September 1994 while conducting habitat and ectotherm inventories within the Red Cap Creek drainage of Humboldt County, in northwestern California. The specimen was captured, examined, photographed, measured and released. Photographic vouchers, along with a description of the specimen, and a discussion of its significance in light of further observations on R. boylii, in the drainage of the albino’s origin, are presented. The discovery of a fully-albino specimen provides an indirect measure of the reproductive success of a population, as albino births occur at a rate of approximately 1:20,000. This would tend to support the hypothesis that the R. boylii population in the Red Cap watershed is a relatively healthy one, and appears to exhibit a high degree of reproductive success.
PCWA (Placer County Water Agency). 2007. AQ 12-Special Status Amphibian and Aquatic Reptile Technical Study Report. Middle Fork American River Project, FERC Project No. 2079. Auburn, CA. [http://relicensing.pcwa.net/html/science/padreportaquatic.php]
Peek, R. 2010. [Sierra Nevada] Landscape Genetics of Foothill Yellow-Legged Frogs (Rana boylii) in regulated and unregulated rivers: Assessing connectivity and genetic fragmentation. University of San Francisco. Masters Thesis, pp. 1-69.
The stream breeding foothill yellow-legged frog (Rana boylii) is experiencing range wide population declines. Because this species inhabits rivers in the foothills of California, a suite of anthropogenic impacts, including habitat alteration, river regulation, aerial drift of pesticides, and invasive species, directly and indirectly affects these frogs. Among multiple stressors, hydroelectric projects may have the greatest potential impact on R. boylii because of flow regulation and riverscape alterations such as dams, reservoirs, and powerhouses. River regulation can fragment the landscape and reduce the connectivity within and among R. boylii populations, which ultimately may limit gene flow and reduce genetic diversity. Determining gene flow and levels of genetic diversity within and among populations in regulated systems compared with unregulated rivers can provide valuable information about population structure and riverscape connectivity for conservation management. This study tests the hypothesis that R. boylii populations in watersheds regulated by hydroelectric generation have lower genetic diversity and riverscape connectivity compared with unregulated watersheds (without hydroelectric generation or dams). Six different rivers in the Sierra Nevada were compared using over 30 km of river and pairing similar-sized hydroelectric-regulated and unregulated rivers in adjacent watersheds. Genetic structure within and among R. boylii populations in regulated and unregulated watersheds was characterized and compared using mitochondrial DNA (mtDNA) in 62 frogs to estimate gene flow and random amplified polymorphic DNA (RAPD) in 98 frogs to estimate genetic diversity. Riverscape connectivity was analyzed with a quantitative geo-spatial network analysis using stream networks, tributary confluences, frog location and distribution patterns. Results indicated significant differences in population structure between regulated and unregulated streams, with breeding and adult locations in regulated rivers indicating frog distributions occur closer to tributary confluences. In addition, R. boylii populations in regulated study rivers generally exhibited lower genetic diversity and greater genetic drift, not associated with isolation by distance compared with unregulated rivers. This species has adapted to inhabit a dynamic ecosystem, and flow regulation has altered the pattern of natural hydrologic variation. As a result, R. boylii populations are currently becoming isolated at genetic and spatial scales, limiting potential adaptive plasticity required to survive within these regulated watersheds.
PG&E (Pacific Gas and Electric). 2009. Second Year Foothill Yellow-Legged Frog Visual Encounter Surveys and Breeding Habitat Assessment in the Lower McCloud River. Updated July 2009, Technical Memo 29. McCloud-Pit Project, FERC Project No. 2106. San Francisco, CA. [http://www.mccloud-pitrelicensing.com].
Rombough, C.R. and M.P. Hayes. 2005. [North Coast] Novel Aspects of Oviposition Site Preparation By Foothill Yellow-Legged Frogs (Rana boylii). Northwestern Naturalist, Vol. 86 pp. 157-160.
Recently, Wheeler and others (2003) reported a heretofore-undescribed behavior wherein female foothill yellow-legged frogs, Rana boylii, scrape the rocky substrate with their hind feet prior to oviposition. They observed that this behavior loosened algae and sediment and postulated that it could enhance the ability of egg masses to adhere to the substrate. Based on 2 episodes at a site in northwestern California, their observations provide a 1st glimpse of this behavior. Here, we add serial observations of this behavior by 2 additional female R. boylii from western Oregon. These observations increase our knowledge of substrate preparation behavior and suggest that females of this species evaluate oviposition site quality.
Sparling, D.W. and G.M. Fellers. 2008. [All Regions] Toxicity of two insecticides to California, USA, anurans and its relevance to declining amphibian populations. Environmental Toxicology and Chemistry. Vol. 28 (8), pp. 1696-1703.
Contaminants have been associated with population declines of several amphibian species in California (USA). Pesticides from the Central Valley of California are transported by winds into the Sierra Nevada Mountains and precipitate into wet meadows where amphibians breed. The present study examined the chronic toxicity of two of the insecticides most commonly used in the Central Valley and found in the mountains, chlorpyrifos and endosulfan, to larval Paciﬁc treefrogs (Pseudacris regilla) and foothill yellow-legged frogs (Rana boylii) and discusses the implications of this toxicity to declining amphibian populations. Larvae were exposed to the pesticides from Gosner stages 25 to 26 through metamorphosis. The estimated median lethal concentration (LC50) for chlorpyrifos was 365 g/L in P. regilla and 66.5 g/L for R. boylii. Time to metamorphosis increased with concentration of chlorpyrifos in both species, and cholinesterase activity declined with exposure concentration in metamorphs of both species at Gosner stages 42 to 46. For endosulfan, the estimated LC50 was 15.6 g/L for P. regilla and 0.55 g/L for R. boylii. All R. boylii exposed to concentrations of greater than 0.8 g/L died before they entered metamorphosis. Pseudacris regilla remains relatively abundant and is broadly distributed throughout California. In contrast, R. boylii is among the species experiencing severe population declines. The present study adds to the increasing evidence that pesticides are very harmful to amphibians living in areas that are miles from sources of pesticide application.
Twitty, V., D. Grant, and O. Anderson.1967. Amphibian orientation: an unexpected observation. Science. Vol. 155: 352-353.
The study of homing movements of displaced newts (Taricha rivularis) revealed unexpected features of the migratory behavior of amphibians. Newts leaving the breeding stream in the spring move not directly uphill but at an angle carrying them upstream. When they emerge after summer estivation this tendency is not evident in captures made during the autumn and winter. During the latter period, however, newly metamorphosed frogs (Rana boylii) show the same pronounced upstream migration that characterizes T. rivularis in the spring.
Van Wagner, T.J. 1996. [Sierra Nevada] Selected life-history and ecological aspects of a population of foothill yellow-legged frogs (Rana boylii) from Clear Creek, Nevada County, California. Master’s Thesis. Department of Biological Sciences. California State University, Chico.
A mark and recapture study conducted from October 1991 to January 1996 was employed to investigate aspects of the natural history and population ecology of a population of foothill yellow-legged frogs (Rana boylii). This study included movement patterns, population density, age-size relationships, growth rates, habitat, winter activity and location, and reproductive ecology. The study was conducted along 810 m of Clear Creek, Nevada County, California, a low order Sierra Nevada foothills stream. Frogs were captured and marked with a unique toe clip code, weighed and measured for snout-urostyle length, sexed and their position and habitat noted along the creek. Data were gathered on spawning activity including: onset and termination dates of spawning, egg mass counts, mesoscale habitat and oviposition substrate, and other oviposition site variables. A diet analysis was conducted using specimens from the study site and from California State University, Chico, vertebrate museum specimens. Of the 1,597 total frog captures, 236 frogs were captured two or more times. One frog was captured seven times over a period of 888 days and another 19 times over 784 days. Jolly-Seber population density estimates ranged from 0.61 to 0.19 frogs/m of stream reach. Size-age relationships of R. boylii showed much overlap within each age class and between sexes. A minimum snout-urostyle length of 17 mm was observed for a juvenile and a maximum s-u length for an adult female of 69 mm was observed. A maximum age of two years was achieved by both sexes; however a single female frog appeared to achieve a maximum age of ≥ years. Mean growth rates of juveniles (≤ 1 yr. old) were greater than adults (≥ 1 yr. old) and adult females grew significantly faster than adult males. Rana boylii in the non-spawning season (June–February) appeared to show habitat philopatry and typically moved short distances. However, a maximum distance moved of 555 m over 95 days was observed during this period by a juvenile. An adult (≥ 1 yr. old) female moved 413 m and an adult male moved 408 m, both during the pre-spawning/spawning seasons (March–May). Adult frogs moved significantly greater distances during the pre-spawning/spawning seasons (mean=54 m) than in the non-spawning (mean = 27 m). Fall captured juvenile frogs exhibited no clear upstream or downstream movement patterns when subsequently recaptured in another season. Adult female frogs appeared to favor deeper pools, whereas adult males and juveniles of both sexes showed no clear trends, utilizing runs, riffles, glides, and pools about the same amount. Rana boylii were located in all winter months (November–February). They were found both in the water and along the stream-edge habitat beneath rocks, leaf litter, and Carex sp. Frogs appeared to be active whenever ambient conditions were favorable. Oviposition commenced as early as mid-April and continued as late as mid-May. A minimum of 14 days and a maximum of 31 days were noted from the beginning to end of oviposition. A minimum of 9 (1992) and a maximum of 35 (1994) egg masses were counted during three spawning seasons. A negative mean daily percent change in mass of adult male R. boylii during the pre-spawning/spawning season contrasted with positive mean daily percent change in mass for juveniles during this season and for both adults and juveniles during the non-spawning season. This suggests high energetic investment for reproductively active adult males. Diet analysis showed that R. boylii fed primarily on terrestrial arthropods (87.5% insects and 12.6% arachnids) at all times of the year, including winter.
Werschkul, D. F. and M.T. Christensen. 1977. Differential predation by Lepomis macrochirus on the eggs and tadpoles of Rana. Herpetologica. Vol. 33, 237-241.
Bluegill sunfishes (Lepomis macrochirus) were offered eggs and tadpoles at different developmental stages of Rana sphenocephala and Rana areolata. The fish ate significantly more tadpoles than eggs. There was no significant difference between predation on the two species or tadpole stage. Rana sphenocephala eggs stripped of the jelly were eaten in significantly higher amounts than eggs with jelly. However, eggs without jelly were eaten in significantly lower amounts than tadpoles. The differential predation on the eggs and tadpoles resulted from the presence of the jelly, and possibly the immobility of the egg did not release a predatorial response from the fish.
Wheeler, C. 2007. [North Coast] Temporal breeding patterns and mating strategy of the Foothill yellow-legged frog (Rana boylii). California. California State University, Humboldt. Masters Thesis.
This study investigated the temporal breeding patterns, mating strategy, and associated behaviors of the Foothill Yellow-legged Frog, Rana boylii, in order to identify the type of mating system utilized. It was conducted on a naturally dynamic, primarily rain-driven and un-regulated stream, in an area with high frog densities relative to many other populations within the range of the species. Data were collected from spring of 2002 to fall of 2003 at Hurdygurdy Creek, in Del Norte County, California. A 20m2 breeding site that consisted of shallow glide and riffle habitat was monitored for temporal patterns in frog breeding activity. Mark-recapture was used to track individuals over space and time and strategic behavioral observations were recorded to investigate aspects of the mating strategy. The duration of breeding activity varied, lasting six weeks in 2002 and three weeks in 2003. Breeding activity was influenced by the day of the breeding season (e.g., early, mid, late), stream flow, and year. Male frogs aggregated at the breeding site during the reproductive season (April-May), but female arrival was asynchronous. Male frogs had attachment to and vocally and/or physically maintained individual sites (< 1m2 on average) within the breeding area. The daily operational sex ratio of adults attending the breeding site was male-biased, while the overall breeding season operational sex ratio was female-biased. Males in amplexus were larger than males never observed in amplexus, providing evidence of female mate selection. Results indicated that these frogs were facultative in regards to duration of breeding activity and were not exclusively prolonged or explosive breeders. However, frog behaviors at the breeding site were more typical of prolonged breeding anurans.
Wheeler, C. A., H. H. Welsh, and L. L. Heise. 2003. [North Coast] RANA BOYLII. (Foothill Yellow-Legged Frog) Oviposition Behavior. Herpetological Review. Vol. 34 (3):234.
Wheeler, C.A. and H.H. Welsh Jr. 2008. [North Coast] Mating Strategy and Breeding Patterns of the Foothill Yellow-legged Frog (Rana boylii). Herpetological Conservation and Biology. Vol. 3 (2), pp. 128-142.
The Foothill Yellow-legged Frog (Rana boylii) has declined across much of its native range in California. Improper stream management may lower egg mass survival and reduce the availability of suitable breeding habitats. We collected data during six breeding-seasons (2002-2007) along an unregulated stream in northwestern California. We monitored temporal reproductive patterns at a breeding site and used mark-recapture and behavioral observations to spatially and temporally track individuals and investigate aspects of the mating strategy. The duration of breeding activity lasted three to seven and a half weeks. Day within the breeding-season and stream flow influenced breeding activity. Male frogs congregated at the breeding site during the reproductive season but females arrived asynchronously. Male frogs showed fidelity to individual sites within the breeding area. The daily operational sex ratio of adults was male-biased, while the overall breeding-season operational sex ratio was female-biased. Males in amplexus were larger than males never observed in amplexus, providing evidence of a non-random mating pattern. These frogs showed plasticity in temporal breeding patterns and were not exclusively prolonged or explosive breeders. Frog behaviors at the breeding site were more typical of prolonged breeding anurans. Both timing and duration of breeding were closely linked to the natural hydrologic cycle, indicating that behavior and annual output of these frogs.
Wiseman, K. 2004. [Sierra Nevada] Foothill Yellow-Legged Frog (Rana boylii) Predation by the Introduced Signal Crayfish (Pacifasticus leniusculus) in the North Fork Feather River, CA. Oral presentation at California/Nevada Declining Amphibians Population Task Force Annual Meeting. Reno, NV.
As part of ongoing monitoring of foothill yellow-legged frog (Rana boylii) populations on the North Fork Feather River (Butte and Plumas Co., CA) for Pacific Gas and Electric's FERC relicensing projects, we employed an underwater video camera to document potential predation of R. boylii embryos and tadpoles. Between 16 and 27 June 2003, we operated an Aqua-Vu® underwater video camera at two known R. boylii breeding sites. Analysis of over 92 hours of videotape revealed that the introduced signal crayfish (Pacifasticus leniusculus) prey upon the egg masses of R. boylii. Five other species were also observed around egg masses and tadpole groups including four species of fish (two non-native species) and Sierra garter snakes (Thamnophis couchii). Results of visual encounter surveys suggested that P. leniusculus also prey upon larval stages of R. boylii, based upon observations of tail injuries. Pacifasticus leniusculus is present in large numbers in this drainage and has been observed in other systems where R. boylii are found, including the Pit and Stanislaus Rivers. Although the extent of predation upon R. boylii by crayfish is not known, other studies demonstrate that crayfish can have devastating impacts upon all life stages of native amphibians. Further research is needed to explore both the indirect and direct effects of signal crayfish on R. boylii populations in order to assess the potential impact this exotic species may have on the ecology and distribution of the foothill yellow-legged frog..
Yarnell, S. 2000. [Sierra Nevada] The Influence of Sediment Supply and Transport Capacity on Foothill Yellow-Legged Frog Habitat, South Yuba River, California. M.S. Thesis. UC Davis.
This study focuses on using process-based geomorphic techniques to discern aquatic habitat preferences of the Foothill Yellow-legged Frog (Rana boylii) in an effort to constrain links between watershed conditions, stream processes and aquatic habitat. Previous studies have examined aquatic habitat using static channel descriptors such as width, depth and grain size, but these characteristics do not reflect the dynamic nature of fluvial systems. Two fundamental features of aquatic habitat, channel shape and substrate texture, were examined using at-a-station hydraulic geometry and a dimensionless bedload transport rate, q*. These channel characteristics were then compared to the seasonal distribution of R. boylii age classes along Shady Creek, a tributary of the South Yuba River in the northern Sierra Nevada which is recovering from past aggradation of hydraulic mining sediment. The hydraulic geometry results revealed that three basic channel morphologies occur on Shady Creek, each dominated by different fluvial processes, while the q* results suggested differences in substrate texture may be due to local variation in sediment supply. The single channel morphologies (termed as ‘confined’ types) were defined by bankfull processes and remained velocity-dominated year-round. The braided channel morphologies were largely characterized by the unconsolidated nature of hydraulic mining sediments, and thus subject to the effects of seasonal variation in flow. As a result, certain ‘alternating’ braided channels were width-dominated at flows equal to or exceeding bankfull flows and velocity-dominated at low flows, while other ‘broad’ braided channels remained width-dominated regardless of flow. Spatial variability observed in q* indicated that while Shady Creek is currently recovering from past aggradation, local sediment supply conditions create differences in the rate of recovery, and thus locally variable channel bed surfaces textures occur. Analyses of these geomorphic measures with R. boylii population density suggested habitat preferences based on age class and season are directly related to channel shape and bed surface texture. Young R. boylii preferred ‘alternating channel morphologies where they can utilize swift, narrow channels in fall during low flows, and then retreat to wide, shallow banks with protected overflow areas in spring during high flows. Adult R. boylii were found most often in the ‘confined’ channel types, which provide deep, narrow, protected pool habitats year-round. Comparisons with q* reveal young R. boylii prefer relatively low-mobility channel substrates dominated by larger grain sizes, while adult frogs may prefer habitats with an intermediate mobility where bedforms as well as large grain sizes are prevalent. The complex dynamic interactions of channel shape and substrate mobility over time and space can be examined using these process-based techniques, and when related to aquatic habitat preferences, provide an analytical link between watershed conditions, fluvial processes and habitat suitability.
Yarnell, S. 2005. [Sierra Nevada] Spatial Heterogeneity of Rana boylii Habitat: Physical Processes, Quantification and Ecological Meaningfulness. Dissertation. UC Davis.
Analysis of the heterogeneity of stream habitat and how biological communities respond to that complexity are fundamental components of ecosystem analysis that are often overlooked. The Foothill Yellow-legged Frog (Rana boylii) is known to associate with various stream habitats throughout its lifecycle and thus may require some degree of habitat complexity at a larger reach scale for a population to persist. The physical processes driving stream hydraulic and geomorphic conditions, such as the relationship between the sediment supply and transport capacity, likely influence the degree of habitat heterogeneity that results. Through a series of three studies, this project addressed the relationships between stream habitat heterogeneity, the supply/capacity ratio, and the physical habitat requirements of R. boylii. Rana boylii habitat associations were quantified throughout a single season to obtain insight into local hydraulic and geomorphic conditions preferred by each lifestage. The best predictors of habitat associations by lifestage were velocity and substrate size, two key characteristics of geomorphic units such as riffles and pools. Results indicated R. boylii occurred in stream reaches with a variety of geomorphic habitats suitable to multiple lifestages. The spatial heterogeneity of geomorphic units was then quantified using several indices from landscape ecology. Indices of spatial composition, such as Shannon’s Diversity Index, were found to correlate well with frog abundance, while indices of spatial configuration, such as Contagion, were not significant. Lastly, Shannon’s Diversity Index, as an ecologically meaningful spatial metric, was compared with a supply/capacity ratio calculated for each study reach in order to assess how relative sediment supply correlated with varying degrees of habitat heterogeneity. Results indicated that in simple channels where only flow and alluvial sediment interacted to create bed topography, maximum heterogeneity occurred with a moderate relative sediment supply. In complex channels where structural elements, such as large woody debris and boulders, created local scour and deposition, habitat heterogeneity increased as the percent of structural elements increased. Project results imply restoration practices and land use changes that affect the relative sediment supply and local geomorphic processes in a stream may directly impact the suitability of habitat complexity required by R. boylii.
Yarnell, S., J.F. Mount, and E.W. Larsen. 2006. [Sierra Nevada] The influence of relative sediment supply on riverine habitat heterogeneity. Geomorphology. Vol. 80 (3-4) pp. 310-324.
The diversity of aquatic habitats in streams is linked to physical processes that act at various spatial and temporal scales. Two components of many that contribute to creating habitat heterogeneity in streams are the interaction between sediment supply and transport capacity and the presence of local in-stream structures, such as large woody debris and boulders. Data from previously published flume and field studies and a new field study on tributaries to the South Yuba River in Nevada County, California, USA, were used to evaluate the relationship between habitat heterogeneity, local in-stream structural features and relative sediment supply. Habitat heterogeneity was quantified using spatial heterogeneity measures from the field of landscape ecology. Relative sediment supply, as expressed by the sediment supply/transport capacity ratio, which controls channel morphology and substrate textures, two key physical habitat characteristics, was quantified using a dimensionless bedload transport ratio, q*. Calculated q* values were plotted against an ecologically meaningful heterogeneity index, Shannon's Diversity Index, measured for each study reach, as well as the percent area of in-stream structural elements. The results indicate two potential mechanisms for how relative sediment supply may drive geomorphic diversity in natural river systems at the reach scale. When less mobile structural elements form a small proportion of the reach landscape, the supply/ capacity ratio dictates the range of sediment textures and geomorphic features observed within the reach. In these settings, channels with a moderate relative sediment supply exhibit the highest textural and geomorphic diversity. In contrast, when less mobile structural elements are abundant, forced local scour and deposition creates high habitat heterogeneity, even in the presence of high relative sediment supply.
Zweifel 1955. [All Regions] Ecology, distribution, and systematics of frogs of the Rana boylei group. University of California Publications in Zoology. Vol. 54 pp. 207-291.
The boylei species group of the genus Rana is seen to be composed of six species: boylei, muscosa, tarahumarae, pustulosa, pueblae, and moorei. The group presents a disjunct distribution, two species being found in California and Oregon and the others in Mexico, one of which barely crosses the border into southern Arizona. The Pacific Coast species boylei and muscosa were formerlyconsidered to be subspecifically related, along with the form sierra, which is here treated as a synonym of muscosa. Boylei and muscosa are here demonstrated to be specifically distinct on the basis of structural evidence, limited sympatry, and low viability of experimental interspecific hybrids. All the species of the group are stream dwellers, although muscosa also enters lakes at high altitudes. Where it does so, it is in the absence of any competing lake or pond-adapted species. The largely allopatric ranges of the species muscosa and boylei are believed to reflect the similarity of adaptation of the two, in that competition prevents any extensive overlap. By way of contrast, aurora and boylei occupy different though slightly overlapping ecologic niches and show very extensive geographic overlap. Breeding experiments show that boylei and muscosa have embryonic stages adapted to cool water, probably differing in this respect from the summer-breeding Mexican members of the group. Increasingly drier conditions in the later Tertiary probably brought about the geographic break between the Pacific Coast and Mexican members of the group. With gradual elimination of summer rainfall from the Pacific Coast region in the course of the Tertiary, the frogs of that region became adapted to breeding in cooler waters in the spring, whereas the Mexican frogs continued to breed in the summer. The disjunct distribution of muscosa in the mountains of central and southern California probably dates from an early interglacial period following a glacial maximum of the Pleistocene. Rana boylei probably invaded southern California at a later time from the Coast Ranges of the state.