- Amy Lind - Tahoe and Plumas National Forests. Note: this person is no longer a Forest Service Research & Development employee.
The California Energy Commission, Energy-Related Environmental Research Program contributed funding for the development of this topic area.
Foothill Yellow-legged Frog (Rana boylii)
River regulation can vary seasonally and regionally based on flow management and operation type. Various factors may impact R. boylii at multiple scales, depending on the life stages involved. For example, flow fluctuations can directly reduce R. boylii fecundity by scouring or desiccating egg masses, reducing reproductive viability for a given year. Changes in flow regime may also have long-term impacts, including vegetation encroachment, altered channel morphology, and reduced breeding habitat (Table 1). Thus, the effects of river regulation on R. boylii can occur at both short-term and long-term scales, and effective management requires careful consideration of both (Table 1).
Table 1. Overview of River Regulation Impacts to Rana boylii (adapted from Kupferberg et al. 2009b).
[E-Egg mass; T-Tadpole; Y-Young of year; J-Juvenile; A-Adult]
|River Regulation Factors||Short-term impacts||Long-term impacts|
||- (E) scour and/or desiccation of egg masses1,2 / tadpoles3
- (T/Y/J, A) export spring and summer algal productivity4,5, reduced resources for tadpoles, reduced insect abundance5, food web repercussions
- (E/T)changes to margin water temperature, depth, and velocity,
- (E/T)scouring/desiccation of eggs/tadpoles, depending on ramping rate, magnitude of change, channel shape
|-(J/A) discharge decoupled from environmental cues (e.g. rainfall, air temperature) triggering inappropriate behavioral responses by adults, juveniles, delayed onset of breeding1,6
- (A) smaller population sizes1,2
Reduced winter/spring flows
|- (E/A) absence of scouring/depositional flows that prevent riparian encroachment
- E/A) reduced breeding habitat, greater distances between breeding sites3
|- (E/T/A) vegetation encroachment, altered channel morphology, reduced breeding habitat
- (All/J/A) population loss/fragmentation3, reduced gene flow, altered metapopulation dynamics
|Altered summer baseflows||- (E/T) lower water temperatures
- (All) change in available habitat (channel shape)
|- (E/T/Y/J) promotes habitats that support non-native predatory fish, amphibians, and invertebrates, increased predation on eggs, tadpoles|
|Movement of water among river basins||- (All) potential for increased disease and parasite transmission||Unknown|
Seasonal River Regulation Effects
River regulation effects R. boylii differently depending on the type of flow regulation, the season, and life stage. Generally, differences between a natural flow regime and a regulated flow regime can be visualized using a hydrograph that shows the change in river flow over time. Although hydrographs can vary within watersheds or regions, general patterns exist for Mediterranean driven climates such as California, and regulated hydrographs tend to diverge from these natural patterns. The following table illustrates these differences between flow regimes, and the life stage effects associated with altered flow regimes.
Table 2. Differences between natural and altered flow regimes and regulated life stage effects on R. boylii.
|Natural Flow Regime||Flows fluctuate with storm and snow-melt events in early spring and then begin gradual recession into summer.||Flow recession continues with relatively low and stable flows by mid-summer.||Flows begin to rise, some fluctuations with early storm events||Flows fluctuate with storm and run-off events|
|Altered (Regulated) Regimes||Aseasonal pulsed flows and other rapid flow fluctuations||Aseasonal pulsed flows and other rapid flow fluctuations; higher than natural base flows||Aseasonal flow changes due to maintenance outages||Reduction in winter flooding - lack of channel shaping flows|
|LIFE STAGE||REGULATED FLOW REGIME EFFECTS|
Vegetation encroachment, altered channel morphology, reduced oviposition habitat
|Tadpole||Stranding/Scouring; export of spring and summer algal productivity, reduced insect abundance/food web repercussions; colder water temperatures; Promotes habitats that support non-native invasive fish, amphibians, and invertebrates with increased predation on eggs, tadpoles||Stranding/Scouring; Changes in algal food base|
|Young Of Year||Limited mobility during metamorphosis -Discharge decoupled from environmental cues (e.g. rainfall, air temperature) triggering inappropriate behavioral responses||Unknown|
|Juvenile||Exports spring and summer algal productivity, leads to reduced insect abundance, food web repercussions||Discharge decoupled from environmental cues (e.g. rainfall, air temperature) triggering inappropriate behavioral responses by juveniles,||Unknown||Unknown|
|Adult||Reduced breeding habitat and greater distances between breeding sites, reduced insect abundance, food web repercussions; delayed onset of breeding because of aseasonal flows, population loss/fragmentation, reduced gene flow, altered metapopulation dynamics, smaller population sizes||Discharge decoupled from environmental cues (e.g. rainfall, air temperature) triggering inappropriate behavioral responses||Unknown||Unknown|
Stage change at egg mass location in regulated river (upper and lower images taken approximately 6 hours apart), Photo R. Peek