Rana yavapaiensis Platz and Frost, 1984
Lowland Leopard Frog
Michael J. Sredl1
1. Historical versus Current Distribution. Historically, lowland leopard frogs (Rana yavapaiensis) were distributed from northwestern Arizona through central and southeastern Arizona, southwestern New Mexico, and northern Sonora, Mexico. Populations also were known from southwestern Arizona and southeastern California along the lower Colorado River and in the Coachella Valley (Platz and Frost, 1984; Platz, 1988; Jennings, 1995a). Identity of leopard frogs in southwestern Utah, southeastern Nevada, and extreme northwestern Arizona has been problematic (Platz, 1984; Jennings, 1988a; Jaeger et al., 2000). This account follows the taxonomy of Jaeger et al. (2000) and considers frogs of the Virgin River downstream into the Black Canyon of the Colorado River below Hoover Dam in Nevada to be relict leopard frogs (Rana onca). Distribution of lowland leopard frogs, like other leopard frogs in the western United States, is fragmented and discontinuous due to the aridity of the region (Mecham, 1968c).
Interpreting historical distribution and abundance data for species of leopard frogs in the western United States is difficult for several reasons: (1) many of them are recently described and similar in appearance (Jennings, 1994); (2) multiple species can inhabit the same locality (Platz and Platz, 1973); and (3) their populations are prone to large fluctuations (Sredl et al., 1997). Historical records for lowland leopard frogs are known from Mohave, Yavapai, Coconino, La Paz, Maricopa, Gila, Pinal, Graham, Greenlee, Yuma, Pima, Santa Cruz, and Cochise counties, Arizona; Catron, Grant, and Hidalgo counties, New Mexico; and San Bernardino, Riverside, and Imperial counties, California (Vitt and Ohmart, 1978; Clarkson and Rorabaugh, 1989; Jennings and Scott, 1991; Jennings and Hayes, 1994b; Sredl et al., 1997). Historical records for lowland leopard frogs also exist from northern Sonora, Mexico, although the range of this species in Mexico is poorly known (Platz, 1988). Elevations of lowland leopard frog localities range from near sea level to 1,817 m (Jennings and Hayes, 1994a; Sredl et al., 1997).
Vitt and Ohmart (1978) surveyed numerous localities along the lower Colorado River and concluded that populations of leopard frogs, which would now be considered lowland leopard frogs, in that area may be extinct. All post-1980 records from the lower Colorado River and in the vicinity of the Salton Sea have turned out to be Rio Grande leopard frogs (Rana berlandieri), which have established themselves in the lower Colorado River and Gila River to Phoenix, Arizona (Platz et al., 1990; Jennings and Hayes, 1994a; Rorabaugh et al., in review). During surveys conducted between 1983 and 1987 of the Arizona and California portions of its range, Clarkson and Rorabaugh (1989) found lowland leopard frogs at only 5 of 10 historical sites and 3 new sites; no extant population was found in California. The most recent California record for lowland leopard frogs was collected in 1965 from an irrigation ditch east of Calexico (Jennings and Hayes, 1994b). Lowland leopard frogs, if they are still present in California, are extremely rare (Jennings and Hayes, 1994a). Sredl et al. (1997) conducted 1,104 surveys within the range of lowland leopard frogs in Arizona and confirmed their presence at 43 of 115 sites that had prior records and 61 new sites; many of the extant populations found were in central Arizona. Jennings (1995a) found lowland leopard frogs at none of six historical sites visited in 1995. A single lowland leopard frog (specimen confirmed by R.D. Jennings) observed in August 2000 in Hidalgo County (Christman and Painter, unpublished data) was the first confirmed observation in New Mexico since 1985 (Jennings, 1995a; R.D. Jennings, personal communication). Additional populations may still occur at or near historical localities in Hidalgo County (Scott, 1992), but their status in New Mexico seems dire (Jennings, 1995a). Little is known of the status of populations in Mexico.
2. Historical versus Current Abundance. Little is known of historical abundance of lowland leopard frogs. Zweifel (1968b) characterized leopard frogs as “abundant” at well-watered sites in valleys of southeastern Arizona. In other parts of southeastern and east-central Arizona, frogs that were likely lowland leopard frogs were abundant and widespread (Wright and Wright, 1949; J.T., Bagnara, personal communication). Like other leopard frogs in the Southwest, these frogs can be abundant where they occur (10–20 frogs jump with each step along the shoreline) or they can be quite scarce (personal observations).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding migrations as have been described for some amphibians have not been noted in lowland leopard frogs. In most populations, breeding usually follows springtime emergence after a period of winter inactivity and continues through summer and into fall. Populations occupying geothermal springs or at low elevations are likely active year-round (R.D. Jennings, unpublished data).
Egg masses have been observed from January through late April and October (Ruibal, 1959; Collins and Lewis, 1979; Frost and Platz, 1983). Reproductive activity may decrease between the time temperatures warm in mid May to prior to the onset of the summer rains in early July (unpublished data).
In populations examined, sex ratios generally do not differ from 1:1 (Sredl et al., 1997). Male lowland leopard frogs attract a potential mate by emitting an airborne call consisting of a series of low pulses lasting 3–8 s (Platz and Frost, 1984). Proximate cues that stimulate mating in lowland leopard frogs are not well studied, although rainfall and water temperature have been mentioned as cues for other leopard frog species in the Southwest.
Ruibal (1959, 1962) studied the physiological ecology of a brackish water population of lowland leopard frogs in southern California. Salinities at this site ranged between 6.0 and 9.0‰. Minimum lethal salinity of eggs was 5‰, while that of adult frogs was 13.0‰ (Ruibal, 1959). Reproduction in a tributary, which was less saline, likely explained persistence of the brackish water frog population (Ruibal, 1959). The upper and lower thermal limit of developing eggs in this population was 29 ˚C and 11 ˚C, respectively (Ruibal, 1962).
ii. Breeding habitat. Lowland leopard frogs inhabit aquatic systems in desert scrub to pinyon-juniper (Platz and Frost, 1984). They are habitat generalists and breed in a variety of natural and manmade aquatic systems. Natural systems include rivers, permanent streams, permanent pools in intermittent streams, beaver ponds, cienegas (= wetlands), and springs; while manmade systems include earthen cattle tanks, livestock drinkers, canals, irrigation sloughs, wells, mine adits, abandoned swimming pools, and ornamental backyard ponds (Platz and Frost, 1984; Scott and Jennings, 1985; Sredl and Saylor, 1998). The preponderance of historical localities are small to medium-sized streams and rivers (R.D. Jennings, 1987; Sredl and Saylor, 1998). In lotic habitats, they are concentrated at springs, near debris piles, at heads of pools, and near deep pools associated with root masses (R.D. Jennings, 1987; unpublished data).
The constant flow and warm water temperature of thermal springs, which permit year-round adult activity and winter breeding, and depauperate fish communities make these sites particularly important breeding habitat for leopard frogs in New Mexico (Scott and Jennings, 1985).
i. Egg deposition sites. Females deposit spherical masses attached to submerged vegetation, bedrock, or gravel. Eggs usually are deposited near the surface of the water (Sartorius and Rosen, 2000).
ii. Clutch size. Has not been studied.
C. Larvae/Metamorphosis. Altig et al. (1998) describe the tadpoles of lowland leopard frogs. In the wild, egg masses have been observed to hatch in 15–18 d (Sartorius and Rosen, 2000). Tadpoles may metamorphose in the same year they were oviposited or overwinter (Collins and Lewis, 1979), and length of larval period may be as short as 3–4 mo or as long as 9 mo (unpublished data). Jennings (1990) found that tadpoles of Chiricahua leopard frogs in warm springs appeared to grow continuously, while growth of those in cold water sites appeared to be arrested during the winter. Lowland leopard frog tadpoles would likely exhibit the same pattern (R. Jennings, personal communication).
D. Juvenile Habitat. Some spatial and temporal separation of adult and juvenile lowland leopard frogs may enhance survivorship. Seim and Sredl (1994) studied the association between juvenile and adult stages and pool size and found that juveniles were associated more frequently with small pools and marshy areas while adults were associated more frequently with large pools.
E. Adult Habitat. Although no study examining habitat use by adult lowland frogs has been conducted, lowland leopard frogs are found in a variety of natural and manmade aquatic systems within its range. Duration of water in these habitats ranges from semi-permanent to permanent. In semi-permanent aquatic systems, lowland leopard frogs may survive the loss of surface water by retreating into deep mud cracks, mammal burrows, or rock fissures (Howland et al., 1997).
The role of habitat heterogeneity within the aquatic and terrestrial environment is unknown but likely important. Shallow water with emergent and perimeter vegetation provide basking habitat, and deep water, root masses, undercut banks, and debris piles provide refuge from predators and potential hibernacula (R.D. Jennings, 1987; Platz, 1988; Jennings and Hayes, 1994b; unpublished data).
Sredl et al. (1997) estimated populations at six lowland leopard frog sites in Arizona. These sites ranged in elevation from 658–1,134 m and 30-yr average rainfall of 233–480 mm/yr. Common riparian overstory at these sites consisted of Fremont cottonwoods (Populus fremonti), willows (Salix spp.), seepwillows (Baccharis glutinosa), mesquite (Prosopis spp.), and introduced salt cedars (Tamarix chinensis). Common ground cover in moist areas included yerba-mansa (Anemopsis californica), canyon ragweeds (Ambrosia ambrosioides), and arrow-weeds (Tessaria sericea). Three-square rushes (Scirpus americanus), spike rushes (Eleocharis spp.), and introduced Bermuda grass (Cynodon dactylon) lined the banks or perimeter of ponds and slackwater pools. The largest, deepest pools had stands of narrow-leafed cattails (Typha angustifolia); large ponds in addition to having cattails, had pondweeds (Potomageton spp.).
Severe fragmentation and alteration of aquatic habitats in the southwestern United States has likely constricted wide ranging aquatic species such as the lowland leopard frog into isolated pockets, and maintenance of aquatic corridors may be critical to their future viability (Jennings and Scott, 1991). Sredl and Howland (1995) speculate that distribution of extant leopard frog populations in Arizona may be reflective of habitat fragmentation and extinction without recolonization as well as habitat quality.
Effects of livestock grazing on amphibian populations may be positive or negative (Jennings, 1988b; Rosen and Schwalbe, 1998; Sredl and Saylor, 1998). In the late 1800s and early 1900s, construction of earthen cattle tanks in upland drainages became a common range management practice (U.S. General Accounting Office, 1991), one that continues to this day. Because they were built primarily to water livestock, a positive secondary benefit of these systems is the water and aquatic habitat they provide to many species of wildlife, including amphibians.
Overgrazing negatively impacts amphibian habitat by removing bankside cover, increasing ambient ground and water temperatures, destroying bank structure (e.g., eliminating undercut banks), trampling egg masses, and adding high levels of organic wastes (Jennings, 1988b). Overgrazing in upland habitats also may degrade amphibian habitat by increasing runoff, which can lead to increased sedimentation of pool habitat in the drainages below (Jennings, 1988b; Belsky and Blumenthal, 1997).
Although the relationship between the lowland leopard frog and non-native predators (e.g., American bullfrogs [Rana catesbeiana], crayfish, and predatory fish) has not been studied in detail, there is a negative co-occurrence between them (Rosen et al., 1995; Fernandez and Rosen, 1996). Among other factors, Sredl et al. (1997) attributed the low frequency of native leopard frog populations in mainstem rivers to the presence of large populations of non-native organisms.
F. Home Range Size. No study of home range has been completed. Sredl (1996) used repeated captures of lowland leopard frogs from a site that had been divided into 50 m sections. Of all captures, 46% were from the same section of initial capture, and 86% of all captures were within two sections of initial capture.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Little is known of seasonal migrations. In one case, following drying of a pond, 154 frogs moved about 250 m upstream to a pond that did not dry, while 4 frogs moved 900 m downstream (Sredl, 1996).
J. Torpor (Hibernation). Although metamorphosed lowland leopard frogs generally are inactive between November and February, a detailed study of wintertime activity and habitat use has not been done.
K. Interspecific Associations/Exclusions. Throughout its range, lowland leopard frogs have been observed to occur with tiger salamanders (Ambystoma tigrinum), Sonoran Desert toads (Bufo alvarius), Great Plains toads (B. cognatus), Arizona toads (B. microscaphus), red-spotted toads (B. punctatus), Woodhouse’s toads (B. woodhousii), canyon treefrogs (Hyla arenicolor), Pacific treefrogs (Pseudacris regilla), Chiricahua leopard frogs (Rana chiricahuensis), Tarahumara frogs (R. tarahumarae), and western narrow-mouthed toads (Gastrophryne olivacea; Campbell, 1934; Ruibal, 1959; Platz and Frost, 1984; R.D. Jennings, 1987; Hale and Jarchow, 1988; Clarkson and Rorabaugh, 1989; unpublished data).
Lowland leopard frogs can be sympatric with another member of the Rana pipiens complex, Chiricahua leopard frogs; but where sympatry occurs, F1 hybrids are rare and presumed backcross individuals were not detected (Platz and Frost, 1984).
Rosen et al. (1995) noted a strong negative co-occurrence between lowland leopard frogs and introduced American bullfrogs. Jennings and Scott (1991) questioned the importance of the role that American bullfrogs have played in declines of native amphibians in the southwestern United States, arguing that many populations in New Mexico that declined were impacted by factors other than American bullfrogs.
L. Age/Size at Reproductive Maturity. Size at metamorphosis for lowland leopard frogs ranges from 25–29 mm SUL (Platz, 1988). The smallest males to exhibit secondary sexual characteristics from study sites in Graham and Yavapai counties, Arizona, were 53.5 mm and 56.2 mm SUL, respectively (Sredl, unpublished data). Size at which females reach sexual maturity is not known. Females have a mean asymptotic SUL of 76.4 mm, while that of males is 63.1 mm (Sredl et al., 1997).
M. Longevity. Preliminarily, skeletochronology of lowland leopard frogs indicates that they can live as long as 3 yr (M.J.S. and P. Fernandez, unpublished data). Estimates of survivorship of the adult and juvenile “age classes” appear to follow a seasonal pattern (Sredl et al., 1997)—high in the spring and summer and lower in the fall and winter. Within any given year, survivorships were always lowest in the winter. In 3 of 4 yr for which there were estimates for all four intervals, wintertime survivorship was by far the lowest; this pattern held for both adults and juveniles.
N. Feeding Behavior. No comprehensive studies of the feeding behavior or diet of lowland leopard frog larvae or adults have been conducted. Larval lowland leopard frogs are herbivorous. The diet of lowland leopard frog adults likely contains a wide variety of insects and other arthropods (Degenhardt et al., 1996). Stomach analyses of other members of the leopard frog complex from the western United States show a wide variety of prey items, including many types of aquatic and terrestrial invertebrates (e.g., snails, spiders, and insects) and vertebrates (e.g., fish, other anurans [including conspecifics], and small birds; Stebbins, 1951).
O. Predators. Detailed studies of predators of lowland leopard frogs have not been done. Tadpoles are likely preyed upon by insects, including belostomatids, notonectids, dytiscids, and anisopterans, and vertebrates, including native and non-native fish, tiger salamanders, garter snakes (Thamnophis sp.), mud turtles (Kinosternon sonoriense), great blue herons (Ardea herodias), and other birds. Potential predators of juvenile and adult frogs likely include native and non-native fish, American bullfrogs, mud turtles, garter snakes, great blue herons, black hawks (Buteogallus anthracinus), and mammals including rats, coyotes, gray foxes, raccoons, ringtail cats, coatis, black bears, badgers, skunks, bobcats, and mountain lions. Cannibalism, primarily large adults eating juvenile frogs or large larvae, is likely but has not been studied. Jones (1990) studied the diet of black-necked garter snakes (Thamnophis cyrtopsis) in two desert streams in Arizona and found adult and larval lowland leopard frogs to be the most frequently consumed prey of adult and subadult snakes.
P. Anti-Predator Mechanisms. Adult lowland leopard frogs are cryptically colored and will sometimes remain motionless to escape detection. Other times, they rely on saltation, escaping to deep water or shoreline cover (personal observations). Jennings and Hayes (1994a) showed a picture taken by R. Ruibal of a lowland leopard frog in a defensive posture. Although others have noted this posture, its specific purpose and effectiveness have not been investigated.
Q. Diseases. In 1998, chytrid fungus was implicated in declines of amphibians in Australia and Panama (Berger et al., 1998). That same year, it was first identified in Arizona (Milius, 1998). Presently, one salamander (Sonoran tiger salamander [Ambystoma tigrinum stebbinsi]), seven species of ranid frogs (Rio Grande leopard frogs, plains leopard frogs [R. blairi], American bullfrogs, Chiricahua leopard frogs [R. chiricahuensis], Ramsey Canyon leopard frogs [R. subaquavocalis], Tarahumara frogs, and lowland leopard frogs), and one treefrog, canyon treefrogs, have been affected by this fungus in Arizona (Sredl et al., 2000; Collins, unpublished data). All outbreaks have been cool-season phenomena, and the pathogen appears widely distributed throughout central and southeastern Arizona (Sredl et al., 2000).
R. Parasites. Goldberg et al. (1998b) examined parasites of lowland and Chiricahua leopard frogs and American bullfrogs collected in Arizona and found that none of the helminths identified from the two native species were found in the American bullfrog.
4. Conservation. Lowland leopard frog populations appear vulnerable to large-scale mortality, on a frequent basis, at the hands of a variety of causative factors. In 1991, Sredl et al. (1997) used mark-recapture to study six populations of lowland leopard frogs. In only 2 yr, each of six study sites showed substantial mortality events, sometimes followed by recovery (Sredl et al., 1997). At the site with the largest population, high rainfall and subsequent flooding during the winter of 1993 caused approximately 90% mortality. By the end of 1993, however, the population was nearly back to pre-flood size, although age structure had shifted toward younger age classes. In the second largest population, an outbreak of chytridiomycosis, which was retrospectively diagnosed, caused 50–80% mortality of metamorphosed frogs in late 1992 and early 1993. Adult frogs were affected to a lesser degree than juveniles. Reduction in total habitat area due to siltation of several important pools preceded and may have exacerbated the die-off. Population recovery from the epidemic has been modest and siltation continues to degrade the remaining habitat (unpublished data). Chytridiomycosis affected another population. In 1992–'93 at two other small populations, declines also took place, and these populations were apparently extirpated. A fourth small population was apparently extirpated in 1992, but recolonized in 1994. It is likely that similar changes in abundance occurred in lowland leopard frog populations historically, although the role chytridiomycosis played is unknown at this time.
Because of suspected declines and extirpation of historical localities, lowland leopard frogs were added to the list of Category 2 candidate species (U.S.F.W.S., 1991). Later, the U.S. Fish and Wildlife Service discontinued the designation of multiple categories of candidates, and only those taxa meeting the definition of the former Category 1 candidate were considered candidates. At this time, lowland leopard frogs were dropped from consideration as a candidate species for Federal listing (U.S.F.W.S., 1996).
1Michael J. Sredl
Arizona Game and Fish Department
2221 West Greenway Road
Phoenix, Arizona 85023-4399
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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