Natural History of
Foothill Yellow-Legged Frogs (Rana boylii)
Ryan Peek | 2023-05-09
Natural History
While this is a single species workshop…
emblematic of the plight of freshwater biota globally
Natural history matters
no accurate observations, no way to know what is happening
Freshwater Biodiversity:
Hotspots of diversity and decline
- We still don’t know much
- Amphibians are declining faster than can be documented
Need for natural history insights & assessment!
Freshwater Patterns: Howard et al. 2015
Significant proportion is vulnerable
Freshwater Patterns: Howard et al. 2015
Status assessed for <50% of taxa
Freshwater Patterns: Howard et al. 2015
A Story of Repeating Life
- In ancient Egypt, frogs represented repeating life
- symbols of fertility and the number 100,000
- displayed with a “Shen” ring (infinity) meant eternal repeating life
Rana boylii
- First described by Baird (1854)
- Later recognized as distinct species by Zweifel in 1955, looked at 565 adults and juveniles.
- Max body size ~73mm (SVL)
- Adults typically >=35mm
Distribution
Extant in for ~5-8 million yrs (Macey et al. 2001)
Obligate river breeder, uses wide range of habitat, disturbance adapted
gone from >50% of historical range
Distribution
- Historical range from Upper San Gabriel River in CA to Willamette Valley, OR
- Two specimens were collected in 1965 in Baja California (Loomis 1965), but never detected after (Welsh 1988, Hollingsworth 2000, Grismer 2002, Stebbins 2003).
Life History
So much to know!
So much we don’t know!
We will give the distilled version
Life History
THE BASICS
- Adults breed in the spring (amplexus)
- Females pick oviposition location
- External fertilization, 1 egg mass per year
- After hatching tadpoles cannot swim ~5 days
- Tadpoles require 2.5 months at 18C or greater
- Metamorphosis in late summer/fall
Species ID: Who’s who?
Species ID: Who’s who?
Other species can appear similar
Other species can appear similar
RABO can have many colors/textures
Different eggs
Different eggs
Extant pops can be evaluated by counting egg mass density
Can be compared through time and space
Good indicator of population size/health
Tadpoles eat, also swim
Lotic tadpoles but better swimmers when small
Experiments showed increasing Gosner stage decreased swim velocity
Adults: Time to Maturity
- Growth curves indicate time to maturity:
- 2 years on the coast
- 3 in Sierras
Adults: Longevity
- Mark/recapture of ~12 yr old in NF Feather by GANDA staff!
- More recent work confirms much longer life-spans possible
Questions?
