Rana luteiventris Thompson, 1913
Columbia Spotted Frog
Jamie K. Reaser1
David S. Pilliod2
1. Historical versus Current Distribution. Columbia spotted frogs (Rana luteiventris) were initially recognized as Rana pretiosa (Baird and Girard, 1853c) and considered widespread throughout much of western North America, ranging in elevation from sea level to nearly 3,040 m in the Rocky Mountains. Taxonomic subdivision into Rana pretiosa luteiventris for the Great Basin region and Rana pretiosa pretiosa for the rest of the species range was proposed (Thompson, 1913), and these subspecies names occur in the scientific literature until the early 1970s. However, the morphological variations (e.g., ventral coloring) were not consistent, and the subspecies designation was contested and eventually abandoned (Turner and Dumas, 1972). In 1996, studies of allozyme variation discerned two spotted frog species whose distributions were not concordant with the original subspecies boundaries (Green et al., 1996, 1997). Oregon spotted frogs (Rana pretiosa) occur in south-central Washington, the Cascade Mountains of Oregon, and extreme southwestern British Columbia. Historically, Oregon spotted frogs occurred in the Pit River system in California (Hayes, 1997), but have not been seen there since 1911 (Stebbins and Cohen, 1995). Columbia spotted frogs, considered in this account, range from extreme southeast Alaska south through British Columbia and Alberta, western Montana and Wyoming, northern and central Idaho, northeastern Oregon, and eastern Washington. Isolated relict populations of Columbia spotted frogs persist in the Great Basin paleodrainages of the Humboldt River (eastern Lahontan Basin), Bonneville Basin, southeastern Oregon, southwestern Idaho, and northern Nevada drainages of the Snake River, and the Big Horn Mountains east of the continental divide of Wyoming (Dunlap, 1977; Bos and Sites, 2001). Columbia spotted frogs might persist in low numbers on the east side of Warner Mountain Chain in California (Jennings and Hayes, 1994a). This species has been reported at elevations up to 1,951 m in Washington and 2,247 m in Oregon (Leonard et al., 1993); 3,036 m in Montana (Maxell et al., 2003); 2,725 m in Idaho (Munger et al., 1997a,b; Pilliod, 2001); 2,890 m in Wyoming (Turner, 1960; Dunlap, 1977; Patla, 1997; D. Patla and C. Peterson, unpublished data); and 2,650 m in the Toiyabe Range of central Nevada (Reaser, 1997a).
No subspecies are currently recognized. However, allozyme data suggest delineation of distinct populations (Green et al., 1996, 1997): Northern, Great Basin, West Bonneville, and Wasatch Front. The recent molecular study by Bos and Sites (2001) revealed four well-supported clades defined on the basis of monophyly of a mtDNA sequence; these included Northern Rocky Mountain, Lahonton, Bonneville, and Deep Creek clades that were recognized by those authors as “candidate Evolutionary Significant Units.” Other studies are in progress and are also expected to reveal divisions within the species currently recognized as R. luteiventris (J.H. Howard and J.C. Munger, in progress; D.M. Green, personal communication). These divisions may prove to be distinguishable on both a molecular and morphological basis (Hayes, 1997; J.K.R., personal observation).
The similarity of native ranids of western North America has led to many mis-identifications of other species as R. pretiosa (= R. luteiventris [Turner and Dumas, 1972]). Reaser (2003) evaluated 57 voucher collections (1912–'73) with specimens identified as R. pretiosa (= R. luteiventris) from Nevada. As a result, vouchers collected from 11 surveys, representing at least five independent sites, were reclassified as Rana draytonii (California red-legged frogs).
2. Historical versus Current Abundance. Only one historical population data set exists for which to make direct comparisons. In Wyoming, Patla and Peterson (1994, 1999) documented an 80% decline in a population of Columbia spotted frogs near Lodge Creek in Yellowstone National Park that went from 1,000–1,900 frogs in the 1950s (Turner, 1960) to 200–400 frogs in the 1990s. This decline is likely the result of construction of a road bisecting habitats used by frogs and of the development of the key spring head where the frogs spend the winter (Patla and Peterson, 1999).
Recent surveys provide anecdotal evidence of changes in abundance and provide baseline data for future comparisons. Across much of the range of the northern population (Idaho, western Montana, eastern Oregon, and northwestern Wyoming), Columbia spotted frogs are common and usually abundant in many areas. In central and northern Idaho and western Montana, Columbia spotted frogs are the most commonly encountered frog species with locally abundant populations, especially in fishless lakes and ponds (O'Siggins, 1995; Munger et al., 1997a,b; Beck et al., 1998; Llewellyn and Peterson, 1998; Yeo and Peterson, 1998; Pilliod, 2001; Maxell et al., 2003). Columbia spotted frogs are often locally abundant across the northern half of eastern Oregon, especially in the Blue and Wallowa Mountain system (M. Hayes and E.L. Bull, personal communication). More than a decade (1989–2002) of amphibian surveys in the Greater Yellowstone Ecosystem of Wyoming indicate that Columbia spotted frogs are geographically widespread and the second most abundant amphibian in the region (Koch and Peterson, 1995; Patla and Peterson, 1995; Patla, 1997; Van Kirk et al., 2000).
Isolated distinct populations along the southern boundary of the species' range have patchy distributions—while some populations are high density, others are not. In the Bighorn Mountains in Wyoming, the population is restricted to a single watershed and only three breeding sites have been identified (Dunlap, 1977; Bos and Sites, 2001). Surveys conducted in southwestern Idaho determined that Columbia spotted frogs are sometimes locally abundant, although limited in distribution (Munger et al., 1996, 1997a,b; Engle and Munger, 1998). In eastern Oregon, anecdotal data suggest that Columbia spotted frogs have disappeared from some lower elevation areas (e.g., some of the Grande Ronde Valley, in the vicinity of Pendleton and Prineville). In this region, populations on private land may be critical for the persistence of the species. Recent surveys of potential breeding habitats in the southern half of eastern Oregon and northern Nevada suggest that Columbia spotted frogs are rare, populations are small, and some declines may have occurred (Wente and Adams, 2002). For example, Wente and Adams (2002) found frogs in 13 of 20 (65%) historical sites visited.
In the Toiyabe Range (central) and the Ruby Mountains (northeast) of Nevada, Reaser (1997a) found Columbia spotted frogs to be uncommon but at high densities (10–20/150 m2) at some sites. These sites may have been acting as refugia during especially dry summer seasons. In northern Nevada, in the vicinity of the Jarbidge and Independence ranges, Reaser (1997a) found Columbia spotted frogs to be more common, but typically at low densities. Columbia spotted frogs often were encountered at beaver ponds. Private land management does not appear to be favoring spotted frogs in Nevada; frogs could not be detected at 14 of the 15 historical sites on private land at which spotted frogs were known to occur in Nevada prior to 1993. Half of historical sites owned by the U.S. Forest Service and 1/3 of the historical Bureau of Land Management sites were also without frogs. However, these surveys also documented 78 sites at which spotted frogs had not been recorded previously.
In Utah, Columbia spotted frogs were found in 2 historical sites out of 25 locations in the Wasatch Front populations (Utah Division of Wildlife Resources Progress Report, 1991). Seven populations are currently known to exist in the Wasatch Front, and although some threats to these populations still exist, ongoing conservation actions have improved the long-term viability of the species (U.S.F.W.S., 2002d). Molecular evidence suggests that Columbia spotted frogs within the Bonneville basin occur as 13 genetically distinct populations that currently have restricted gene flow (Bos and Sites, 2001). The West Bonneville populations have been inventoried thoroughly, and the many disjunct populations appear to be large enough to be considered secure at this time (Ross et al., 1994).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Adult Columbia spotted frogs emerge in late February to early July depending on the latitude, elevation, and seasonal weather patterns (generally later at higher latitudes and elevations). Males typically are reported to emerge before females (3–4 d), but in southwest Idaho populations in 1999, male and female breeders emerged simultaneously in mid April. There were, however, many more males than females (J.C. Engle, personal communication). If wintering habitat does not meet criteria for reproduction, spotted frogs are required to migrate to breeding sites. These movements often occur along wetland (ephemeral or permanent) corridors and sometimes overland (see Turner, 1960; Morris and Tanner, 1969; Patla, 1997; Pilliod et al., 2002). The arid landscape and present climatic conditions in Tule Valley of Utah likely prevent frequent movement of frogs between the six spring complexes (Hovingh, 1993), except perhaps in wet years.
ii. Breeding habitat. Population-specific reports are highly variable, reflecting the diversity of habitats available within the range of the species. In general, Columbia spotted frogs use the shallows (only a few cm deep) of lentic habitats (lakes, ponds, marshes, and small springs) for breeding and egg deposition. These habitats are usually permanent (or were so prior to recent degradation), although naturally ephemeral pools are used successfully by some populations. Springs are often nearby. Aquatic substrates may be fine textured and unconsolidated. Floating and/or emergent vegetation are usually present. Percent sun exposure is typically high. Spotted frogs usually breed in fish-free habitats, or in isolated pools adjacent to lakes with fish, when available (Munger et al., 1997a,b; Reaser, 1997a; Hoffman and Pilliod, 1999; Pilliod and Peterson, 2001). However, Columbia spotted frogs can breed successfully in some water bodies with fish (i.e., sites with dense emergent vegetation in the littoral zone). Columbia spotted frogs will use human-created wetlands (Monello and Wright, 1999). Surrounding habitat is quite variable, from arid desert shrub to montane forest. Water temperatures are often well below 18 ˚C (65 ˚F; see Turner, 1960, 1962; Stebbins, 1962, 1985; Morris and Tanner, 1969; Hovingh, 1993; Reaser, 1997a; Behler and King, 1998; ).
i. Egg deposition sites. Egg laying occurs in the spring, often under conditions where water freezes at night. This occasionally results in high egg mortality (Licht, 1971; D.S.P., unpublished data). Oviposition sites are normally in the part of the wetland that has the warmest water temperatures, typically associated with shallow water (10–20 cm deep) and high solar radiation (often the north side). Egg masses sometimes become attached to vegetation and/or one another. Egg masses usually become colonized by green algae (possibly Oophila amblystomatis), which may increase egg mass temperatures and increase developmental rates (Gilbert, 1944; D.S.P., unpublished data).
ii. Clutch size. Reports of clutch size vary greatly, even within the same population (ranges of 150–2,400, average about 600; Turner, 1957, 1958; Morris and Tanner, 1969; Cuellar, 1994; Werner et al., 1999; Maxell, 2000). Time to hatching ranges from 8–21 d and is influenced by temperature.
C. Larvae/Metamorphosis. Tadpoles are often found in lentic habitats, but may also occupy lotic (flowing) systems where they move up and down stream, grazing on vegetation (especially green algae such as Spirogyra ) and detritus. Tadpoles typically metamorphose mid to late summer, although they have been observed in Nevada as late as October (Morris and Tanner, 1969; J.K.R., personal observations) and in southwestern Idaho in mid November (J.C. Engle, personal communication). Despite suggestions that spotted frog tadpoles may overwinter at some sites (Logier, 1932; Turner, 1958a), there is no evidence for this in any part of their range.
D. Juvenile Habitat. Juveniles are found in habitats similar to adults (see "Adult Habitat" below; Pilliod et al., 2002), however they are more often found associated with dense emergent and/or floating vegetation (which likely provide cover; Reaser, 1997a). In drying streambeds, juveniles have been found in pooled water under rocks (K. Hatch, personal communication).
E. Adult Habitat. Post- and non-breeding individuals may continuously occupy breeding sites or move into substantially different habitats (e.g., Pilliod et al., 2002). Radio telemetry data suggest that after breeding, adults may move away from breeding sites in order to reduce their risk of predation by garter snakes (Thamnophis sp.) that gather to feed on tadpoles and newly metamorphosed animals (M. Hayes and E.L. Bull, personal communication). Columbia spotted frogs frequent pooled or flowing wetlands (ranging in size from lakes to ditches), moist meadows, and forests. Wetlands may be permanent or ephemeral. Floating and/or emergent vegetation is usually present. In some populations, Columbia spotted frogs are found within dense willow clumps or along talus. Basking sites (exposed banks or vegetation mats) are important. This species will use human-created wetlands. Surrounding habitat ranges from mixed coniferous and subalpine forests to arid grass and brushlands (see Turner, 1960; Morris and Tanner, 1969; Stebbins, 1985; Reaser, 1997a; Pilliod, 2001).
F. Home Range Size. Movement is likely greatest in places where predator risk is high, food is scarce (or more unpredictable), or wetlands are ephemeral; these factors likely vary from site to site. Carpenter (1954) and Turner (1960) reported that individually marked Columbia spotted frogs moved within a region of tens to thousands of m2, generally returning to the vicinity of initial capture. However, spotted frogs within a study conducted by Hollenbeck (1976) did not exhibit behavior indicative of a restricted home range. Reaser (1997a; unpublished data) found that site fidelity typically was high, however movement patterns varied with extent of rainfall, with animals dispersing more widely (as much as 5 km/yr; Reaser, 1996b) in "wet years." In some populations, individuals annually migrate between breeding, summer foraging, and overwintering sites, covering areas of > 20 ha (Pilliod, 2001). In a high elevation basin of Idaho, Pilliod et al. (2002) found that females frequently make longer migrations than males; males appear to remain closer to breeding sites. However, in southwestern Idaho, J.C. Engle (personal communication) observed that males and subadults tend to move greater distances than females.
G. Territories. Columbia spotted frogs are not known to defend occupied sites.
H. Aestivation/Avoiding Dessication. Skeletochronology (counting of growth rings in bone) reveals that some individuals within Nevada’s populations may undergo brief periods of arrested growth during the summer (Reaser, 2000b). However, in this same region, frogs were observed to die under severe drying conditions rather than aestivate (Ross et al., 1999). One radio-tagged frog in southwestern Idaho remained buried in mud for several weeks during mid summer (T. Carrigan, personal communication).
I. Seasonal Migrations. When individual wetlands do not meet all life history requirements, frogs are required to move multiple times within a season in order to reach suitable breeding, foraging, and wintering sites. These movements often occur along wetland (ephemeral or permanent) corridors and sometimes overland (Turner, 1960; Patla and Peterson, 1994; Patla, 1997; Bull and Hayes, 2001; Pilliod et al., 2002). Annual migrations of ≥ 2 km between wintering, breeding, and foraging sites (total round-trip distance) have been observed in some high elevation populations (Pilliod et al., 2002). In Oregon, telemetered spotted frogs migrated up to 560 m from breeding ponds to occupy other ponds and river stretches during the summer (Bull and Hayes, 2001).
J. Torpor (Hibernation). Overwintering occurs in springs, spring-fed water holes, beaver dams, on pond bottoms, and on the bottoms and beneath the undercut banks of permanent streams (Turner, 1960; T. Carrigan, personal communication). During the autumn and early spring, frogs have been observed moving into and out of spring mouths and openings in stream banks. In higher latitudes and upper elevation areas, wintering sites probably are characterized by water that does not freeze due to renewal by flow from underground sources or the inlets and outlets of large lakes (Pilliod et al., 2002). Skeletochronology reveals that Columbia spotted frogs experience an extended period of arrested growth corresponding with the winter season (Reaser, 2000b). However, Columbia spotted frogs are not necessarily overwintering in a torpid state. Radiotelemetry data suggest that Columbia spotted frogs can and do move, even under cap ice during the winter season (Bull and Hayes, 2002).
K. Interspecific Associations/Exclusions. “Healthy” populations are often found in habitats supporting a wide variety of other native aquatic species, including dace and suckers (Catostomus spp.). However, introduced char and trout species, such as brook trout (Salvelinus fontinalis), cutthroat trout (Oncorhynchus clarkii), and rainbow trout (O. mykiss), have negatively affected the distribution and abundance Columbia spotted frogs (Munger et al., 1997a,b; Pilliod and Peterson, 2000, 2001). Cutthroat trout prey on spotted frog tadpoles and juveniles (Pilliod, 2001), reducing recruitment in lakes with fish (Hoffman and Pilliod, 1999). In southwestern Idaho, spotted frogs occur in streams supporting native redband trout (J.C. Munger, personal communication). There is little evidence that other species of native amphibians compete for habitat with Columbia spotted frogs (Reaser, 1997a). However, in central Idaho and Montana, long-toed salamanders (Ambystoma macrodactylum) were found at > 80% of wetlands containing Columbia spotted frogs (Werner and Reichel, 1994; O'Siggins, 1995; Munger et al., 1997b; Llewelyn and Peterson, 1998; Pilliod, 2001).
L. Age/Size at Reproductive Maturity. Based on mark-release-recapture studies, Turner (1960) reports that first breeding occurs at 5–6 yr (60 mm TL) for females and 4 yr for males (45 mm TL) in Wyoming. Skeletochronology reveals that males in central Nevada reach reproductive maturity after 1–2 winters (at 35 mm minimum length) and females 1–2 yr later (Reaser, 2000b).
M. Longevity. Turner (1960) estimated (from growth rates) that frogs at a high elevation site in Wyoming reached 12–13 yr for females and 10 yr for males. These estimates are consistent with skeletochronology data from Columbia spotted frog populations at similar elevations in central Idaho (D.S.P., unpublished data). In central Nevada, the oldest female observed via skeletochronology was 7 yr old, while males did not exceed 3 yr (Reaser, 2000b). In southwestern Idaho, the oldest female via skeletochronology was 9 (Engle and Munger, 1998).
N. Feeding Behavior. Feeding takes place both day and night (J.K.R. and R.E. Dexter, unpublished data). Spotted frogs appear to be generalists and opportunistic, even capturing and consuming juvenile conspecifics (Pilliod, 1999). Their primary food includes insects, arachnids, and mollusks. For lists of food items see Thompson (1913), Tanner (1931), Schonberger (1945), Turner (1959), Miller (1978), and Whitaker et al. (1983).
O. Predators. A wide variety of birds (especially herons [Ardeidae] and ravens [Corvus corax; Turner, 1960], American kestrels [Falco sparvericus; Smith et al., 1972], and sandhill cranes [Grus canadensis; J.C. Engle, personal communication]) will feed on Columbia spotted frogs. Other predators include fishes (cutthroat trout [Pilliod, 2001]) and snakes (especially garter snakes [Thamnophis sp.; Reaser and Dexter, 1996a; J.C. Munger, personal communication]). Mammals, including weasels (Mustela sp.), river otters (Lutra canadensis [Pilliod, 2001]), and coyotes (Canis latrans [Turner, 1960; Hovingh, 1993]) also prey upon spotted frogs.
Tadpoles are particularly susceptible to predation by birds, including robins (Turdus migratorius), Brewer's blackbirds (Euphagus cyanocephalus), and ravens (Corvus corax [D.A. Patla, personal communication]), Clark's nutcrackers (Nucifraga columbiana [Pilliod, 2002]), and belted kingfishers (Megaceryle alcyon [Licht, 1974]). Other tadpole predators include aquatic insects (e.g., predacious diving beetles [Coleoptera] and water bugs [Hemiptera]), macrophagous leeches (Hovingh, 1993), and snakes (J.K.R., personal observation). Non-native fishes, including trout, char, and goldfish (Carrasius auratus) are thought to be potentially important predators of spotted frogs (Ross et al., 1993; Munger et al., 1997a,b; Reaser, 1997a; Hoffman and Pilliod, 1999; Monello and Wright, 1999; Pilliod and Peterson, 2000, 2001; Bull and Marx, 2002). Invasive crayfish and American bullfrogs (R. catesbeiana) might also be aggressive predators on various life history stages of spotted frogs (Reaser, 1997a).
P. Anti-Predator Mechanisms. Spotted frogs are sluggish relative to other ranids, and their best defense against sight-cued predators may be to remain still or descend below the water's surface (J.K.R., unpublished data). The color of spotted frogs may vary with habitat type to reduce visibility. For example, darker brown frogs are found along muddy seeps and lighter green frogs are found in algal mats (J.C. Engle, personal communication). In lakes with predacious fish, adults that are startled by researchers are more likely to return immediately to shore as compared with frogs in fishless lakes (D.S.P., personal communication). When captured by snakes, spotted frogs will often twist and turn while thrashing wildly (Reaser and Dexter, 1996a). Occasionally, captured adults utter a “deep clicking” release call. A similar behavior is often observed when they are placed in zip-lock bags. Subadult frogs captured by predacious water bugs emit a piercing, high-pitched scream (J.C. Engle, personal communication); juveniles and adults captured by garter snakes have also been observed to scream (M. Hayes, personal communication; J.K.R, personal observation). Remarkably, few frogs scream when handled by researchers (M. Hayes, personal communication; J.K.R., personal observation). Columbia spotted frogs may release a mild skin toxin—the water in zip-lock bags becomes opaque and foamy, and stings mildly when in contact with open cuts. Some people experience skin that is dried, cracked, and irritated after prolonged handling of the species (J.K.R., personal observation). Heavy metals may decrease the fright response of spotted frog tadpoles to predators in aquatic habitats contaminated by mine tailings (Lefcort et al., 1998).
Q. Diseases. Sickly Columbia spotted frogs have been documented in central Nevada. Observations include emaciation, skin and cornea lesions, ulcerated digits and tarsus, and prolapse of urinary bladder (J.K.R. and D.E. Green, personal observations). Similar symptoms (e.g., emaciation, cornea lesions and blindness, prolapsed bladder) were observed in several individuals in central Idaho and were termed the "wasting disease" by researchers (D.S.P., personal observation). During ice melt-off at a high elevation pond (ca. 2,000 m [6,100 ft]) in the Wallowa Mountains of northeastern Oregon, > 20% of frogs in a 150+ frog sample had a fungal brush-border on the eyelids and/or loss of integrity of the skin of the feet that resulted in spontaneous bleeding with minor handling (M. Hayes and E.L. Bull, personal observation). A large number of the frogs exhibiting these conditions were recaptured 2 mo later; none showed signs of any of the previous conditions. It was surmised that the low dissolved oxygen levels beneath the ice stressed the frogs, allowing fungal establishment. In Nevada, spotted frogs often exhibit an inflammation response to toe clipping (Reaser and Dexter, 1996b; J.K.R., D.L. Drake, and M.A. Hagerty, unpublished data). The presence of a chytrid fungus has been confirmed in sickly frogs at one pond and suspected at several others in the Owyhees of southwestern Idaho (J.C. Munger, personal communication; populations apparently stable at present) and in the Heber Valley population of Utah (Green and Converse, 2002; Green and Sohn, 2002).
R. Parasites. Parasites previously reported from Columbia spotted frogs include Spironoura pretiosa (Ingles, 1936, may have been R. cascadae; J.K.R., unpublished data), Gorgoderina multilobata (Ingles, 1936), Haplometrana utahensis, Gorgoderina tanneri (Olsen, 1937), and Aplectana gigantica (Olsen, 1938). "Ascarid parasitism" was reported by Schonberger (1945). Turner (1958b) reports that of 62 hosts examined, 32 were parasitized by Spironoura pretiosa, 30 by lung flukes (Haematolechus similiplexus and an unknown species of this genus), and 10 by an undetermined species of Glypthelminus. Gorgoderina tanneri infected 8 of 27 frogs examined, and an undetermined species of Halipegus was found in 4 of 46 hosts. No cestodes were found. There were no differences in infections of males versus females. Three trematodes, including Halipegus occidualis, Haematoloechus varioplexus, and Haplometrana intestinalis, were found in 14–51% of 59 spotted frogs examined from five ponds in northern Idaho (Russell and Wallace, 1992). Large adult hosts had the largest infections. Upon necropsy of a sickly specimen from Nevada, D.E. Green (personal communication, 1996) identified a chronic Haplipegus infection of one ear and noted an accumulation of inflammatory cells, fluids, and fluke eggs within the middle ear. Various lesions (skin, ears, lungs, esophagus, stomach, intestines, and urinary bladder) in this animal appeared to have been caused by a variety of parasites (species undetermined). Columbia spotted frogs captured in southwestern Idaho frequently have leeches attached; one frog in 1998 had 14 small leeches (J.C. Engle, personal communication). A few specimens in Utah have been found with the leech Helobdella stagnalis attached to the ventral surface (Ross and Richardson, 1995). This is the third report of this leech species attached to vertebrates, but without further gastric analysis, it is unknown if this leech is actually feeding on the vertebrates (P. Hovingh, personal communication). Johnson et al. (2002) examined Columbia spotted frogs from the Owyhees in Idaho and found low rates of infection by trematodes (Ribeiroia ondatrae) and few individuals with limb deformities.
4. Conservation. Columbia spotted frogs are one of the many species of amphibians in the western United States experiencing declines. Due to documented rarity, loss of populations, and increasing land-use pressures, Columbia spotted frogs of the Great Basin (Nevada and southern Idaho), Wasatch Front (Utah), and West Desert (Utah) were declared warranted (but precluded by work on other species having higher priority for listing) of protection under the Federal Endangered Species Act (Worthing, 1993). It is important to note, however, that this finding pre-dated the availability of molecular data on the distinct populations of R. luteiventris, and, thus, may have underestimated the distinctiveness and vulnerability of some populations. For example, isolated, genetically distinct populations in the Bighorn Mountains of Wyoming have yet to be considered in conservation efforts (Bos and Sites, 2001). It is also possible that efforts to conserve the species since 1993 have improved the status of some populations. For example, according to a report released by the U.S. Fish and Wildlife Service (U.S.F.W.S., 2002d), habitat protection and conservation measures have minimized or removed potential threats such as urbanization, predation, and water depletion as stressors of Utah’s Herber Valley population (the largest and best protected on the Wasatch Front).
The “heritage rank status” for the R. luteiventris was last assigned in July 1997 and took into consideration the molecular studies of Green et. al. (1996, 1997). The results are as follows: Global Heritage Status—G4; Rounded Global Heritage Status Rank—G4; U.S. National Heritage Rank—N4 (see www.natureserve.org).
Pooled water with strong sun exposure, springs, and floating vegetation (and/or other basking sites) are critical components for persistence of Columbia spotted frogs. Any stochastic event or land-use activity (e.g., grazing, removal of beaver and destruction of dams, fragmentation of migration corridors by road building, spring development and water diversion, climate change) that has a negative impact on these landscape elements, or access to them, poses a threat to Columbia spotted frog populations (e.g., Reaser, 1997; Patla and Peterson, 1999; Bull and Hayes, 2000; Maxell, 2000; Engle, 2001). Columbia spotted frogs are also susceptible to displacement or predation by introduced species (e.g., Werner et al., 1998; Pilliod and Peterson, 2001; Bull and Marx, 2002), disease from pathogens and parasites (e.g., Turner, 1958b; Johnson et al., 2002), and chemical contaminants (e.g., Kirk, 1988; Lefcort et al., 1998). Studies conducted by Blaustein et al. (1999) suggest that, at least at the embryonic stage, Columbia spotted frog populations are not presently being limited by UV-B radiation.
In the last decade, the plight of Columbia spotted frogs has received the attention of many biologists, and a considerable amount of work has gone into learning about their ecology and evolution, documenting their current distribution and status, and developing management and monitoring plans. In addition, two habitat restoration projects show promising results for spotted frog conservation. The first project, undertaken by the Bureau of Reclamation in Utah, used the best available information on spotted froghabitat requirements to design and construct wetlands for Columbia spotted frogs as part of a habitat restoration and mitigation project along the Provo River (Ammon et al., 2003). Within 5 yr of construction, approximately 90% of the 17 original constructed wetlands had been colonized and were being used for breeding by Columbia spotted frogs. A population repatriated via egg masses began to reproduce after 2 yr. Approximately 70 additional wetlands have since been constructed and are being monitored for frog use (E. Ammon, personal communication). The second notable conservation project is being conducted on Stoneman Creek in the Owyhee Mountains of southwestern Idaho, where the elimination of beaver had resulted in the loss of breeding habitat for Columbia spotted frogs (J.C. Munger, personal communication). Coincident with the erosion of an inactive beaver dam, a population of > 100 frogs declined to near zero as water tables dropped and oxbows dried. As a restoration effort for spotted frogs, the eroded breech in the dam was repaired and beaver were introduced. One year later, 6 adult and > 200 juvenile spotted frogs were captured in the slack water and oxbows above the dam, and beaver had created several more dams upstream (J.C. Munger, personal communication).
Acknowledgments. We thank Elizabeth Ammon, David Bos, Evelyn Bull, Tim Carrigan, Janice Engle, Kent Hatch, Marc Hayes, Peter Hovingh, Jim Munger, Deb Patla, Chuck Peterson, David Ross, and Jack Sites for their contributions to this account and their ongoing dedication to the conservation of the Columbia spotted frog. Support for DSP was provided by USGS Amphibian Research and Monitoring Initiative during this project.
1Jamie K. Reaser
Ecos Systems Institute
6210 Julian Street
Springfield, Virginia 22150
2David S. Pilliod
Department Biological Sciences
Idaho State University
Pocatello, Idaho 83209
Aldo Leopold Wilderness Research Institute
USDA Forest Service
P.O. Box 8089
Missoula, Montana 59807
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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