Boreal Toad Research Articles

Is forest close to lakes ecologically unique?: Analysis of vegetation, small mammals, amphibians, and songbirds

We compared vegetation structure, flora, and fauna in forest stands at varying distances from small lakes in the boreal mixedwood zone of Alta., Canada, with that in the surrounding upland landscape. We tested the hypothesis that lakeside riparian forest is more structurally diverse, hosts different biotic communities, and has greater floral diversity and greater abundance and richness of other biota, as compared with similar forest in areas far from open water. Lakeside forest was characterized by greater canopy cover, and aspen height and diameter (breast height) than upland forest, but absolute differences were quite small and there was no evidence of greater structural diversity. Contrary to expectations, herb richness and diversity were lower in lakeside forests and the understory community there could not be differentiated from that of upland forests. Two species of anuran amphibians [wood frog ( Rana sylvatica) and boreal toad ( Bufo boreas boreas)] were more abundant in forest up to 100 m from lakes than in upland areas 400–1200 m away from open water. However, differences in abundance between trapping sites in the non-forested riparian zone and sites up to 100 m into the lakeside forest were small. Use of upland habitats by amphibians (juvenile wood frog in particular) was substantial during the latter part of their active season, possibly because they used upland areas for dispersal and overwintering. The two most abundant species of small mammal [red-backed vole ( Clethrionomys gapperi) and deer mouse ( Peromyscus maniculatus)] were trapped less often in the non-forested riparian zone, while the meadow vole ( Microtus pennsylvanicus), meadow jumping mouse ( Zapus hudsonicus), and shrews ( Sorex spp.) were more abundant in those areas. Abundance did not differ significantly among trap lines located in forest from 50 m to >600 m from open water. Songbird abundance and richness were higher near lakes, possibly because of the additional niches available at the forest/lake interface and increased food supply for insectivorous birds. Overall, our results did not strongly support our hypotheses concerning the ecological attributes of lakeside riparian forest. If any part of these lakeside riparian areas can be considered ecologically unique or species-rich it appears to be the non-forested riparian zone and, for birds, the natural lakeshore ecotone (∼50 m into the forest). We encourage those responsible for forest management to re-think prescriptive placement of fixed-width forested buffers around all lakes, and instead consider a landscape-scale planning approach that determines the appropriate placement of uncut forest on the landscape to meet broad conservation objectives.

AN EVALUATION OF WEATHER AND DISEASE AS CAUSES OF DECLINE IN TWO POPULATIONS OF BOREAL TOADS

Two populations of boreal toads (Bufo boreas) experienced drastic declines in abundance in the late 1990s. Evidence supported the hypothesis of disease (the chytrid fungus, Batrachochytrium dendrobatidis) as the cause of these declines, but other hypotheses had not been evaluated. We used an 11-year capture–recapture data set to evaluate weather and disease as causes of these declines. We developed sets of mathematical models that reflected hypothesized relationships between several weather variables and annual survival rates of adult males in these populations. In addition, models that reflected the possibility that the declines were caused by an introduced fungus were developed. All models were fit to the data and were evaluated using a model selection criterion (QAICc). Our analysis provided strong support for the hypothesis of an introduced fungus and little support for the hypothesis that weather conditions caused the declines. Our results also suggest a strong, negative “marking effect” on survival rates of boreal toads. Model-averaged estimates of survival rate are presented.

Anuran gender identification by fecal steroid analysis

AbstractThis study tested the hypothesis that steroid hormone metabolites can be measured in anuran feces and their concentrations used to identify the sex of adults. Fecal samples from American toads, Bufo americanus, and boreal toads, B. boreas boreas, were extracted using ethyl acetate, and the concentrations of estradiol, progesterone and testosterone metabolites were measured by enzyme immunoassays with antibodies commonly used to evaluate steroid hormone concentrations in mammalian species. In American toads, mean testosterone metabolite concentrations (P<0.05) between males (224.3±15.5 ng/g feces) and females (80.7±10.6 ng/g), but estradiol and progesterone metabolite concentrations did not. In contrast, estradiol immunoreactivity differed (P<0.05) between male (19.0±1.8 ng/g) and female (48.3±6.3 ng/g) boreal toads. Progesterone and testosterone metabolite concentrations did not differ. Fecal hormone metabolite analysis offers a promising noninvasive approach to gender identification in anuran amphibians. However, the group of metabolites differentiating gender may not be consistent among species. Zoo Biol 0:1–12, 2005. © 2005 Wiley‐Liss, Inc.

A DNA-based assay identifies Batrachochytrium dendrobatidis in amphibians.

Chytridiomycosis caused by Batrachochytrium dendrobatidis (Chytridiomycota) has been implicated in declines of amphibian populations on four continents. We have developed a sensitive and specific polymerase chain reaction-based assay to detect this pathogen. We isolated B. dendrobatidis from captive and wild amphibians collected across North America and sequenced the internal transcribed spacer regions of the rDNA cassette of multiple isolates. We identified two primers (Bd1a and Bd2a) that are specific to B. dendrobatidis under amplification conditions described in this study. DNA amplification with Bd1a/Bd2a primers produced a fragment of approximately 300 bp from B. dendrobatidis DNA but not from DNA of other species of chytrids or common soil fungi. The assay detected 10 zoospores or 10 pg of DNA from B. dendrobatidis and detected infections in skin samples from a tiger salamander (Ambystoma tigrinum), boreal toads (Bufo boreas), Wyoming toads (Bufo baxteri), and smooth-sided toads (Bufo guttatus). This assay required only small samples of skin and can be used to process a large number of samples.

The effects of ultraviolet‐b radiation on the toxicity of fire‐fighting chemicals

The interactive effects of ultraviolet (UV) and fire-retardant chemicals were evaluated by exposing rainbow trout (Oncorhyncus mykiss) juveniles and tadpoles of southern leopard frogs (Rana sphenocephala) to six fire-retardant formulations with and without sodium ferrocyanide (yellow prussiate of soda [YPS]) and to YPS alone under three simulated UV light treatments. Yellow prussiate of soda is used as a corrosion inhibitor in some of the fire-retardant chemical formulations. The underwater UV intensities measured were about 2 to 10% of surface irradiance measured in various aquatic habitats and were within tolerance limits for the species tested. Mortality of trout and tadpoles exposed to Fire-Trol GTS-R, Fire-Trol 300-F, Fire-Trol LCA-R, and Fire-Trol LCA-F was significantly increased in the presence of UV radiation when YPS was present in the formulation. The boreal toad (Bufo boreas), listed as endangered by the state of Colorado (USA), and southern leopard frog were similar in their sensitivity to these chemicals. Photoenhancement of fire-retardant chemicals can occur in a range of aquatic habitats and may be of concern even when optical clarity of water is low; however, other habitat characteristics can also reduce fire retardant toxicity.

Evidence for disease-related amphibian decline in Colorado

The recent discovery of a pathogenic fungus ( Batrachochytrium dendrobatidis) associated with declines of frogs in the American and Australian tropics, suggests that at least the proximate cause, may be known for many previously unexplained amphibian declines. We have monitored boreal toads in Colorado since 1991 at four sites using capture–recapture of adults and counts of egg masses to examine the dynamics of this metapopulation. Numbers of male toads declined in 1996 and 1999 with annual survival rate averaging 78% from 1991 to 1994, 45% in 1995 and 3% between 1998 and 1999. Numbers of egg masses also declined. An etiological diagnosis of chytridiomycosis consistent with infections by the genus Batrachochytrium was made in six wild adult toads. Characteristic histomorphological features (i.e. intracellular location, shape of thalli, presence of discharge tubes and rhizoids) of chytrid organisms, and host tissue response (acanthosis and hyperkeratosis) were observed in individual toads. These characteristics were indistinguishable from previously reported mortality events associated with chytrid fungus. We also observed epizootiological features consistent with mortality events associated with chytrid fungus: an increase in the ratio of female:male toads captured, an apparent spread of mortalities within the metapopulation and mortalities restricted to post metamorphic animals. Eleven years of population data suggest that this metapopulation of toads is in danger of extinction, pathological and epizootiological evidence indicates that B. dendrobatidis has played a proximate role in this process

Home Range and Movements of Boreal Toads in Undisturbed Habitat

I sampled movements and amount of area used by boreal toads (Bufo boreas) between June and October for 3 yr. Females were found farther from the breeding site than were males, and mean home ranges, as calculated by the adaptive kernel method, were four times larger for females than for males. Temperature and snow accumulation were comparable over the study, but data collection was hampered by mortality of animals caused by an outbreak of amphibian chytridiomycosis in yr 2. These data provide insight into use of habitat by boreal toads in undisturbed areas but may not be typical of a completely healthy population.

Effects of ultraviolet radiation on toad early life stages.

Exposure to harmful levels of ultraviolet-B radiation (UVB), a component of solar radiation, has been suggested as a potential cause of amphibian declines. We measured solar radiation (UVB, ultraviolet-A, and visible) wavebands in breeding ponds of Bufo boreas (boreal toad, a montane species that has undergone severe population declines) and Bufo woodhousii (Woodhouse's toad, a plains toad that has not experienced declines)and examined tolerances of these species to simulated solar UVB exposures in the laboratory. We found larvae of both species to be tolerant of simulated solar UVB in excess of solar UVB levels observed in their breeding ponds. B. boreas tadpoles were more tolerant of simulated solar UVB exposure than B. woodhousii tadpoles, possibly because of greater amounts of photoprotective melanin in B. boreas skin. UVB levels observed in B. boreas habitats do not currently appear to constitute a threat to the survival of these animals; however, long-term (> 1 month) exposure to UVB levels comparable to levels associated with the water interface appears to reduce survival in B. woodhousii tadpoles. Therefore, future increases in surface and water column UVB radiation in bufonid habitats might pose significant survival risks to B. boreas or B. woodhousii populations.

Effects of Incident UV-B Radiation on Periphyton in Four Alpine Freshwater Ecosystems in Central Colorado: Impacts on Boreal Toad Tadpoles (Bufo boreas)

ABSTRACT Field experiments using mylar shielding were conducted to determine the impacts of UV-B on food quality in four western boreal toad breeding ponds located in central Colorado. The breeding ponds were located at elevations ranging from 2971 m to 3272 m, an elevational range associated with at least a 5% change in UV-B exposure. The protein concentration in algae decreased with increased exposure to UV-B, chlorophyll a concentration was not affected by UV-B exposure, and community composition of algae was affected. Densities of Chlorophyta and Xanthophycease increased and densities of Diatomaceae and Cyanophyta decreased under mylar shielding. Not all members of taxonomic groups reacted the same. These data are interpreted to mean that food quality available to boreal toad tadpoles is poorer as a result of increased exposure to UV-B. Poorer food quality can impact the ability of these toads to complete their life cycle and thus can impact recruitment to adult populations.

Experimental Repatriation of Boreal Toad (Bufo boreas) Eggs, Metamorphs, and Adults in Rocky Mountain National Park

Experimental Repatriation of Boreal Toad (Bufo boreas) Eggs, Metamorphs, and Adults in Rocky Mountain National Park

Movements and Habitat Use of Boreal Toads in the Snake River Quarry Area

Nine Boreal toads (Bufo boreas) were captured during the summer of 1999 at the Snake River Quarry and fitted with telemetry transmitters. Locations were determined approximately once each week. Females may be leaving the quarry site around mid-summer while males remain in the area throughout the summer. Toads preferred two aquatic sites until around mid-July then dispersed to dryer terrestrial areas with a preference for 3 sites characterized by loose soil, which provided good burrow shelter. This quarry is to undergo major reclamation efforts. It is recommended to: 1) stay major construction disturbance until the females undertake their seasonal departure from the area, 2 ) preserve the breeding and preferred aquatic habitat and 3) capture male toads from the preferred terrestrial areas and reintroduce them back after reclamation is completed.

An observation of interspecific amplexus between Boreal, Bufo boreas, and Canadian, Bufo hemiophrys, toads with a range extension for Boreal Toad in central Alberta

An observation of interspecific amplexus between Boreal, Bufo boreas, and Canadian, Bufo hemiophrys, toads with a range extension for Boreal Toad in central Alberta

Effects of Ultraviolet Radiation on Boreal Toads in Colorado

Field exposures of Bufo boreas embryos to fractions of ambient UV-B radiation at two sites in Rocky Mountain National Park, Colorado, USA, were conducted to evaluate UV-B as a possible cause of recent severe declines of this species. There were no differences in hatching success of B. boreas embryos exposed to 0–100% of ambient UV-B radiation at either study site, results that are different from those of recent studies in Oregon that found increased mortality of B. boreas embryos exposed to ambient UV-B. The reasons for these differing results are not apparent, and several possible explanations exist, including differences in experimental design, presence or absence of a pathogenic fungus, and geographic genetic variation. Bufo boreas embryos were probably not receiving higher doses of UV-B radiation during the experiments in Oregon compared to the experiments in this study. Results of this study do not support UV-B radiation alone as the cause of the decline of B. boreas during the past 20 yr in the southern Rocky Mountains, but UV-B cannot be dismissed because of the contradictory results from other studies.

Basking by Adult Boreal Toads (Bufo boreas boreas) during the Breeding Season

Basking is a thermoregulatory mechanism by which some ectothermic animals increase their body temperatures by exposing all or some of its body to direct sunlight. Posturing or changing the angle of the body in relation to the sun can increase or decrease the thermal benefits (Brattstrom, 1979). Wet skinned animals, such as toads, are not directly affected by radiant heat exchange (Tracy, 1975; Hoppe, 1979) and are best able to influence their body temperature by behaviorally choosing microhabitats receiving solar radiation (Tracy et al., 1993). While not directly warming the animal, solar radiation warms the substratum and thereby the air near the substratum such that the animal is experiencing a microhabitat warmer than the ambient air temperature. Adult and juvenile toads (Bufo boreas boreas and B. canorus) living at high elevations in western North America are active diurally and have been observed to bask in direct sunlight during mid to late summer, after the breeding season (Mullally and Cunningham, 1956; Mullally, 1958; Campbell, 1970; Lillywhite et al., 1973, Carey, 1978). Summer basking has been documented for other high-elevation anurans, such as Rana muscosa (Bradford, 1984). Daytime breeding activity in a population of B. b. halophilus in southern California has been described by Mullally (1958) and amplexed pairs of B. b. boreas are commonly observed laying eggs during daylight (Campbell, 1970; Corn and Muths, unpub. data). However, basking by adult toads during the breeding season has not been described. Basking may have several physiological benefits (Lofts, 1984; Zapata et al., 1992) but increased exposure might increase the risk of predation by birds, which has been observed in this population (Corn, 1993). We observed basking toads (completely out of the water on emergent rocks and logs) at Kettle Tarn in Rocky Mountain National Park (Larimer County, Colorado; UTM Zone 13, 2810 m elevation) early in the 1995 breeding season. On 3 June from 0955 to 1100 h, we observed 10-15 adult male and three amplexing pairs of B. b. boreas basking (Fig. 1). We observed several other males and nine additional amplexing pairs in the water. The pond was free of ice but was completely surrounded by snow. The sky was clear and temperatures were recorded by thermistor thermometer single-channel data loggers placed at Kettle Tarn on 12 May. Air temperature (measured 10-15 cm above the substratum) was 11.9 C at 1030 h and water temperature (measured at a depth of approximately 10 cm) was 12.2? at 1000 h and 13.6? at 1100 h. Wind was undetectable.

The mount pinatubo eruptions, effects of the atmosphere and climate

Despite prevalent awareness of global amphibian declines, there is still little information on trends for many widespread species. To inform land managers of trends on protected landscapes and identify potential conservation strategies, we collected occurrence data for five wetland-breeding amphibian species in four national parks in the U.S. Rocky Mountains during 2002–2011. We used explicit dynamics models to estimate variation in annual occupancy, extinction, and colonization of wetlands according to summer drought and several biophysical characteristics (e.g., wetland size, elevation), including the influence of North American beaver (Castor canadensis). We found more declines in occupancy than increases, especially in Yellowstone and Grand Teton national parks (NP), where three of four species declined since 2002. However, most species in Rocky Mountain NP were too rare to include in our analysis, which likely reflects significant historical declines. Although beaver were uncommon, their creation or modification of wetlands was associated with higher colonization rates for 4 of 5 amphibian species, producing a 34% increase in occupancy in beaver-influenced wetlands compared to wetlands without beaver influence. Also, colonization rates and occupancy of boreal toads (Anaxyrus boreas) and Columbia spotted frogs (Rana luteiventris) were ⩾2 times higher in beaver-influenced wetlands. These strong relationships suggest management for beaver that fosters amphibian recovery could counter declines in some areas. Our data reinforce reports of widespread declines of formerly and currently common species, even in areas assumed to be protected from most forms of human disturbance, and demonstrate the close ecological association between beaver and wetland-dependent species.

Amphibian Declines in the Greater Yellowstone Ecosystem: Toads with Protection from Bacterial Disease

During the past forty years, biologists have become increasingly concerned about the decline and disappearance of various amphibian species throughout the world (Wyman 1990, Wake 1991). An example of an amphibian decline in western North America is that of the Boreal Toad (Bufo boreas). A previously widespread and abundant species, the Boreal Toad has undergone large population declines and is now a candidate for threatened and endangered status in the eastern half of its range (Stebbins and Cohen 1995, Federal Register 1995). Decreases in Boreal Toad abundance and distribution have been observed in Colorado, eastern Wyoming, and eastern Utah (Com et al. 1989). From 1971-82, eleven Boreal Toad populations disappeared from the West Elk Mountains of Colorado (Carey 1993). During this eleven-year period, numerous individuals were observed exhibiting symptoms of redleg, a well­documented disease in amphibians caused by the bacterium Aeromonas hydrophila (Russel 1898, Emerson and Norris 1905, Kulp and Borden 1942, Reed and Toner 1942, Dusi 1949, Hunsaker and Potter 1960, Hird et. al. 1981, Nyman 1986, Carey 1993). This disease was considered responsible for the decline and ultimate extinction of these eleven toad populations. These extinctions led Carey to propose a hypothesis regarding the disease process which is stated as follows: (1) Some environmental factor or synergistic effects of more than one factor changes sufficiently to cause sublethal "stress;" (2) This stress directly causes suppression of the immune system, or indirectly causes immunosuppression by effecting elevated secretion of adrenal cortical hormones; (3) Immunosuppression, coupled with the apparent effect of cold body temperatures on the ability of immune systems of ectothermic animals to fight disease, leads to infection by Aeromonas or other infectious agents, and to subsequent death of individuals and extinction of populations.

Adaptive, Chemically Mediated Fright Response in Tadpoles of the Southern Leopard Frog, Rana utricularia

breeding success (e.g., Smith, 1987; Berven, 1988). However, foraging may also lead to increased susceptibility to predation. Selective pressures therefore may exist for larvae to balance conflicts between maximizing food intake and minimizing exposure to predators. Furthermore, defenses appropriate for certain predators may be maladaptive for others. For example, reducing movement may decrease detection by visually or pressure-oriented predators (Skelly, 1994), whereas fleeing may be more appropriate for tactile-oriented predators. One way that amphibian larvae may detect predators is through chemical cues given off by predators or injured conspecifics (Petranka et al., 1987; Kats et al., 1988; Lefcort and Eiger, 1993). For example, Kats (1988) found that salamander larvae, (Ambystoma texanum), increased refuge use when exposed to chemical cues from a predacious fish. Similarly, boreal toad larvae (Bufo boreas) avoided areas where giant water bugs (Lethocerus americanus) had recently fed on tadpole conspecifics. Aquatic vertebrates often alter their behavior when exposed to such chemicals, especially in murky water where visual cues are less useful (e.g., von Frisch, 1941; Magurran, 1989; Chivers and Smith, 1993). Rather than reacting to background levels of all potential predators, some tadpoles only respond to predators that have fed on conspecifics. Tadpoles of Rana aurora exhibit a fright response (i.e., they reduce their activity levels) only when exposed to chemical cues from predatory newts (Taricha granulosa) that have fed on R. aurora tadpoles or to an extract of crushed tadpoles (Wilson and Lefcort, 1993). The tadpoles may be reacting to metabolites and undigested parts of prey in the predator's urine and feces.

Hypothesis Concerning the Causes of the Disappearance of Boreal Toads from the Mountains of Colorado

Recent reports of world‐wide declines and extinctions of amphibian populations have raised questions about the relation of environmental change to the demise of certain amphibian species. Between 1974 and 1982, 11 populations of boreal toads (Bufo boreas boreas) in the West Elk Mountains of Colorado totally disappeared. The apparent cause of extinction of these toads was infection with the bacteria Aeromonas hydrophila. In this paper, the presence of disease in declining populations of these toads is used in conjunction with a variety of data from the literature to formulate a working hypothesis for explaining the cause of the decline of this species, and perhaps others: Some environmental factor or synergistic effects of more than one factor changes sufficiently to cause sublethal “stress”; This stress directly causes suppression of the immune system, or indirectly causes immunosuppression by effecting elevated secretion of adrenal cortical hormones; Immunosuppression, coupled with the apparent effect of cold body temperatures on the ability of immune systems of ectothermic animals to fight disease, leads to infection by Aeromonas or other infectious agents and to subsequent death of individuals and extinction of populations.

REPRODUCTIVE ISOLATION IN SONORAN DESERT DROSOPHILA.

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Predation by Gray Jays on Aggregating Tadpoles of the Boreal Toad (Bufo boreas)

Predation by Gray Jays on Aggregating Tadpoles of the Boreal Toad (Bufo boreas)