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Research Topics Wildlife & Fish

Foothill Yellow-legged Frog (Rana boylii)

Ecology

The river-dwelling foothill yellow-legged frog (Rana boylii) is currently a species of special concern in California, and has declined from over 50 percent of its historic range (Davidson et al. 2002, Lind 2005). Research on the ecology of R. boylii has increased our understanding of the habitat requirements (Kupferberg 1996, Yarnell 2005, Lind 2005, Haggarty 2006), development and competition (Kupferberg 1997), basic movement (GANDA 2008, Bourque 2008), phylogeny and genetic structure (Macey et al. 2001, Lind 2005, Dever 2007, Lind et al. 2011), and behavior (Van Wagner 1996, Wheeler and Welsh 2008) of this species.

Genetics

Rana boylii was initially described as a full species by Baird (1854), but endured several name changes before it was commonly recognized as a distinct species in the family Ranidae (Zweifel 1955). Lind et al. (2011) provide a good summary of the phylogenetic and molecular analyses relating to this species. Dever (2007) observed high levels of intra-tributary genetic diversity in R. boylii, and evidence of genetic differentiation among tributaries, in addition to support for reduced gene flow between populations separated by distances greater than 10 km. Lind et al. (2011) analyzed R. boylii mtDNA and observed genetic structuring correlated with hydrologic region and river basin, and strong evidence of among-river basin divergence, indicating genetic variation in this species is highly structured along hydrologic boundaries. Furthermore, Peek (2010) found evidence of greater genetic differentiation in R. boylii populations in regulated rivers (populations separated by reservoir, dam, or mainstem peaking reach) compared with unregulated rivers. Lind et al. (2011) also identified several populations at the extremes of the geographic range that were genetically distinct and warrant conservation attention.

Life History

Adult frogs are found primarily in or near rivers and streams and feed on aquatic and terrestrial insects (Nussbaum et al. 1983, Haggarty 2005). They use low gradient portions of streams for breeding and rearing (Zweifel 1955), but post-metamorphic individuals have been observed in a wide variety of habitats, including those with very steep gradients. Breeding and oviposition occur in the spring and females only deposit a single egg mass per season, consisting of several hundred to over 2,000 eggs (Zweifel 1955, Kupferberg 1996, Lind et al. 1996, Kupferberg et al. 2009c). Breeding occurs in hydraulically stable habitat (generally shallow, low water velocity areas) in rocky substrates, often near cobble or gravel bars with sparse vegetation near tributary confluences (Kupferberg 1996, Lind et al. 1996, Van Wagner 1996, Lind and Yarnell 2008). Initiation of oviposition is generally associated with the descending limb of the hydrograph (receding flow from spring snow melt), increasing day length, and warming of water temperatures, although additional variables may be involved (Zweifel 1955, Lind et al. 1996, Kupferberg 1996, GANDA 2008, Wheeler and Welsh 2008). Larvae emerge from eggs after approximately two weeks, but hatching times may vary depending on water temperatures (Zweifel 1955). Development from hatching through metamorphosis requires approximately three months, depending on water temperature and food availability, and R. boylii do not overwinter as tadpoles (Zweifel 1955). Reproductive maturity may not occur until the frog reaches two to three years in age, and it is unknown whether individuals breed every year (particularly females) (Kupferberg et al. 2009c). Rana boylii use habitat patches for breeding at or near tributary confluences (Kupferberg 1996), and generally seem to prefer heterogeneous habitat areas, such as braided channels or tributary junctures (Kupferberg 1996, Peek 2010).

Habitat

Rana boylii are stream-associated and historically occurred in foothill and mountain streams from northern Baja California to southern Oregon west of the Sierra-Cascade crest, from sea level to approximately 1830 m (6000 ft) elevation (Stebbins 2003). Rana boylii habitat requirements are closely linked to seasonal variation in stream habitats and can be divided into three main categories: breeding and rearing habitat, non-breeding habitat, and overwintering habitat.

Breeding and Rearing Habitat

Breeding and rearing habitat is generally located in gently flowing, low-gradient stream sections, with variable substrate predominated by cobble and boulder (Kupferberg 1996, Van Wagner 1996, Yarnell 2005). Rana boylii breed at locations that provide suitable velocities and depths over a relatively broad range of discharge volumes, including small tributaries and large rivers (Kupferberg 1996, Lind and Yarnell 2008). Egg masses are typically attached to the lee (i.e., flow protected) side of substrate (generally cobble, boulder, or bedrock), near river margins in shallow and relatively slow habitat (see Lind and Yarnell 2008 for range of depths and velocities, Kupferberg 1996). Larvae are found in the same habitat as egg masses, and require protection from scouring flows, particularly immediately after hatching and as larvae near metamorphosis (Kupferberg et al. 2009c)

Breeding and rearing habitat at (a) South Fork  Eel River. Breeding and rearing habitat at (b) Butte Creek.
Breeding and rearing habitat at (a) South Fork Eel River, and (b) Butte Creek (Photos: R.Peek).

Non-breeding Habitat
Post-metamorphic R. boylii remain in terrestrial riparian and riverine habitat adjacent to the wetted channel during the non-breeding season (Bourque 2008, Kupferberg 1996, Lind et al. 1996, Moyle 1973, Van Wagner 1996, Zweifel 1955). Rana boylii have been documented in a wide range of habitats, but all generally occur within a short distance of flowing water (see Bourque 2008) although differences appear to vary both regionally and seasonally (Bourque 2008, Haggarty 2005, Van Wagner 1996, Yarnell 2000, Yarnell 2005).

Overwintering Habitat
Very little data are available relating to overwintering habitat. Van Wagner (1996) observed R. boylii both in the water and along the stream-edge habitat beneath rocks, leaf litter, and Carex sp, and found frogs appeared to be active whenever ambient conditions were favorable. Habitat use in large rivers may vary compared to Van Wagner’s observations, and R. boylii may move into smaller lateral tributaries to avoid risk of scouring (Kupferberg 1996), or move into adjacent terrestrial habitat to avoid winter flood events altogether.


Ecological Details:

(Adapted from Table 1.2 in Ecological relationships of the foothill yellow-legged frog (Rana boylii) [from Lind 2005])

Other Threats & Risks
General Amphibian Decline

Amphibian populations continue to decline on local and global scales (Davidson et al. 2002, Lannoo 2005, Pounds et al. 2006, Hamer and McDonnell 2008, Wake and Vredenburg 2008), and the underlying reasons behind these declines often remain unknown (Moyle and Randall 1998, Beebee and Griffiths 2005, Brito 2008). Human activities have been directly linked to all of the key factors in this recent era of amphibian decline, including climate change, invasive species introductions, habitat fragmentation, and habitat destruction (Karr and Chu 2000, Beebee and Griffiths 2005). Therefore, current amphibian declines may not only represent a severe change in the balance of global biodiversity, but also indicate significant and widespread ecological degradation. This degradation may have ramifications not only for amphibians, but all species that rely on the benefits that "ecosystem services" (Daily 1997) provide, such as drinking water, food supply, purification of human and industrial wastes, and habitat for plant and animal life (Wilson and Carpenter 1999).

Citations
Beebee, T.J.C. and R. A. Griffiths. 2005. The amphibian decline crisis: A watershed for conservation biology? Biological Conservation. Vol. 125, pp. 271–285.

Brito, D. 2008. Amphibian conservation: Are we on the right track? Biological Conservation. Vol. 141 (11), pp. 2912–2917.
Daily, G. 1997. Nature’s services. Island Press, Washington D.C., USA.

Hamer, A. and M. McDonnell. 2008. Amphibian ecology and conservation in the urbanising world: A review. Biological Conservation. Vol. 141 (10), pp. 2432–2449.

Karr J.R. and E.W. Chu. 2000. Sustaining living rivers. Hydrobiologia. Vol. 422/423, pp. 1–14.

Lannoo, D. (ed). 2005. Amphibian Declines. Conservation Status of United States Species. Regents of the University of California, University of California Press.

Moyle, P. B. and P. J. Randall. 1998. Evaluating the biotic integrity of watersheds in the Sierra Nevada, California. Conservation Biology. Vol. 12 (6), pp. 1318–1326.

Pounds, J.A., Bustamante, M.R., Coloma, L.A., Consuegra, J.A., Fogden, M.P.L., Foster, P.N., La Marca, E., Masters, K.L., Merino-Viteri, A., Puschendorf, R., Ron, S.R., Sanchez-Azofeifa, G.A., Still, C.J., Young, B.E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature. Vol. 439 (7073), pp. 161–167.

Wake, D. and V. Vredenburg. 2008. Are we in the midst of the sixth mass extinction? A view from the world of amphibians. PNAS. Vol. 105 (1), pp. 11466–11473.

Wilson, M. and S. Carpenter. 2008. Economic valuation of freshwater ecosystem services in the United States: 1971–1997. Ecological Applications. Vol. 9 (3), pp. 772–783.

Other Risks for Foothill Yellow-Legged Frogs
SuctionDredge_NFMFA
Suction-dredge mining, North Fork Middle Fork American River (Photo: R. Peek)

Rana boylii face a range of risks which adversely affect conservation of populations and their habitat. Major limiting factors include: land use change, shifts in precipitation and climate (Lind 2005, Kupferberg et al. 2009b), parasites and disease (Kupferberg et al. 2009a), toxins /pesticides (Davidson et al. 2002, Davidson et al. 2007, Hothem et al. 2009, Sparling and Fellers 2008), invasive species (Moyle 1973, Kupferberg 1997), and habitat alteration (including fire/fuel management, habitat fragmentation, and mining).

These factors may act synergistically. Recent research has identified synergistic sub-lethal affects of pesticides in relation to the Batrachytrium dendrobatidis (Bd) infection fungus (Davidson et al. 2007), and Kupferberg et al. (2009a) found evidence between unusually warm summer water temperatures and outbreaks of the parasitic non-native copepod Lernaea cyprinacea, and malformations in R. boylii tadpoles and young of the year. Habitat alteration unrelated to flow regulation in the current range of R. boylii continues in the form of urbanization, land use change, and suction-dredge mining.

Last Modified: Mar 28, 2013 03:37:27 PM