FrogLog 103 PDF here - Amphibian Specialist Group

Effects of flow regimes altered
by dams on survival population
declines, and range-wide losses of
California river-breeding frogs
By Sarah J. Kupferberg, Wendy J. Palen, Amy J.
Lind, Steve Bobzien, Alessandro Catenazzi, Joe
Drennan & Mary E. Power
Widespread alteration of natural
hydrologic patterns by large dams
combined with peak demands for power
and water delivery during summer months
have resulted in frequent aseasonal flow
pulses in rivers of western North America.
Native species in these ecosystems have
evolved with predictable annual flooddrought
cycles; thus, individuals and
populations are vulnerable to disruption
of the seasonal synchrony between stable
low-flow conditions and reproduction. We
evaluated whether altered flow regimes
affected two native frogs in California and
Oregon (U.S.A.) at four spatial and temporal
extents. At the two largest geographic and
time scales we examined changes in species
distribution over approximately 50 years
and compared current population density
between 11 regulated and 16 unregulated
rivers. At two finer scales, we assessed
temporal trends in abundance among
populations occupying rivers with different
hydrologic histories, and related withinyear
patterns of early life stage survival to
seasonal hydrology. The Foothill yellow
legged frog (Rana boylii) breeds only in
flowing water and is more likely to be absent
downstream of large dams than in freeflowing
rivers. Breeding populations are
on average five times smaller in regulated
rivers than in unregulated rivers. Time
series data (range = 8 − 19 years) from five
populations of yellow legged frogs and two
populations of California red-legged frogs
(R. draytonii) across a gradient of natural
to highly artificial timing and magnitude
of flooding indicate that a key flow-regime
attribute is variability of flows in spring and
summer. Extreme flow fluctuations due to
pulsed releases from dams, rapid cessation
of spills and natural storm events were
strongly correlated with high mortality
of embryos and tadpoles by scouring
and stranding. Subsequent decreases in
densities of adult females followed after a
lag corresponding to the time for affected
cohorts to reach reproductive maturity. To
balance the increasing demands for water
and hydroelectric power with conservation
of these frogs and other species with similar
phenology, dam operations that better
mimic natural flow timing are needed.
S. J., Kupferberg, et al., Cons. Bio. 26, 513
(2012).
Frog population viability under
present and future climate
conditions: a Bayesian state-space
approach
By Rebecca McCaffery, Antti Solonen &
Elizabeth Crone
World-wide extinctions of amphibians
are at the forefront of the
biodiversity crisis, with climate change
figuring prominently as a potential driver
of continued amphibian decline. As in other
taxa, changes in both the mean and variability
of climate conditions may affect amphibian
populations in complex, unpredictable
ways. In western North America, climate
The Columbia spotted frog (Rana luteiventris) is a pondbreeding
amphibian found at a range of elevations in
western North America. In a high elevation population
of this species in Montana, USA, we found that future
decreases in snowpack are forecast to increase
population viability. Photo: Rebecca McCaffery.
Locations (a) of focal watersheds in California (Alameda Creek, north fork [NF] of the Feather River, south fork
[SF] of the Eel River) and average clutch densities (circles) where breeding censuses of Foothill yellow-legged frog
(Rana boylii) (b) have been conducted in regulated and unregulated rivers. Clutches (c) are attached to rocks, and
remain visible if stranded (d) or until hatching (e). Photo: A. Catenazzi & J. Drennan.
models predict a reduced duration and
extent of mountain snowpack and increased
variability in precipitation, which may have
consequences for amphibians inhabiting
montane ecosystems. We used Bayesian
capture–recapture methods to estimate
survival and transition probabilities
in a high-elevation population of the
Columbia spotted frog (Rana luteiventris)
over 10 years and related these rates to
interannual variation in peak snowpack.
Then, we forecasted frog population
growth and viability under a range of
scenarios with varying levels of change in
mean and variance in snowpack. Over a
range of future scenarios, changes in mean
snowpack had a greater effect on viability
than changes in the variance of snowpack,
with forecasts largely predicting an increase
in population viability. Population models
based on snowpack during our study period
predicted a declining population. Although
mean conditions were more important for
viability than variance, for a given mean
snowpack depth, increases in variability
could change a population from increasing
to decreasing. Therefore, the influence of
changing climate variability on populations
should be accounted for in predictive
models. The Bayesian modelling framework
FrogLog 20 (4) | Issue number 103 (July 2012) | 43