Landscape features such as mountains, rivers, and ecological gradients may strongly affect patterns of dispersal and gene flow among populations and thereby shape population dynamics and evolutionary trajectories. The landscape may have a particularly strong effect on patterns of dispersal and gene flow in amphibians because amphibians are thought to have poor dispersal abilities. We examined genetic variation at six microsatellite loci in Columbia spotted frogs (Rana luteiventris) from 28 breeding ponds in western Montana and Idaho, USA, in order to investigate the effects of landscape structure on patterns of gene flow. We were particularly interested in addressing three questions: (i) do ridges act as barriers to gene flow? (ii) is gene flow restricted between low and high elevation ponds? (iii) does a pond equal a 'randomly mating population' (a deme)? We found that mountain ridges and elevational differences were associated with increased genetic differentiation among sites, suggesting that gene flow is restricted by ridges and elevation in this species. We also found that populations of Columbia spotted frogs generally include more than a single pond except for very isolated ponds. There was also evidence for surprisingly high levels of gene flow among low elevation sites separated by large distances. Moreover, genetic variation within populations was strongly negatively correlated with elevation, suggesting effective population sizes are much smaller at high elevation than at low elevation. Our results show that landscape features have a profound effect on patterns of genetic variation in Columbia spotted frogs.

Inventory, monitoring, and experimental studies have been the primary approaches for documenting and understanding the problem of amphibian declines. However, little attention has been given to placing human-caused perturbations affecting one or more life-history stages in the context of the overall population dynamics of particular species. We used two types of ecological sensitivity analysis to determine which vital rates have the strongest influence on the population dynamics of western toads ( Bufo boreas ), red-legged frogs ( Rana aurora ), and common frogs ( Rana temporaria ), pond-breeding amphibians that have declined in all or portions of their ranges. Our results suggest that post-metamorphic vital rates and highly variable vital rates both have a strong influence on the population dynamics of these species and therefore deserve more research and management attention. Ecological sensitivity analysis should be more widely applied to the issue of amphibian declines in order to identify the most plausible mechanisms of decline and prioritize which lifehistory stages should be the focus of research and management efforts. Future experimental studies of perturbations in one or more life-history stage should attempt to link the magnitude of the perturbation measured with the overall population-level consequences. Finally, current research, inventory, and monitoring efforts should be supplemented with demographic studies so that quantitative analyses can be applied to a wider range of species and life-history groups.

Many proximate causes of global amphibian declines have been well documented, but the role that climate change has played and will play in this crisis remains ambiguous for many species. Breeding phenology and disease outbreaks have been associated with warming temperatures, but, to date, few studies have evaluated effects of climate change on individual vital rates and subsequent population dynamics of amphibians. We evaluated relationships among local climate variables, annual survival and fecundity, and population growth rates from a 9-year demographic study of Columbia spotted frogs (Rana luteiventris) in the Bitterroot Mountains of Montana. We documented an increase in survival and breeding probability as severity of winter decreased. Therefore, a warming climate with less severe winters is likely to promote population viability in this montane frog population. More generally, amphibians and other ectotherms inhabiting alpine or boreal habitats at or near their thermal ecological limits may benefit from the milder winters provided by a warming climate as long as suitable habitats remain intact. A more thorough understanding of how climate change is expected to benefit or harm amphibian populations at different latitudes and elevations is essential for determining the best strategies to conserve viable populations and allow for gene flow and shifts in geographic range.amphibian | climate change | demography | Rana luteiventris | snowpack A mphibian populations are declining around the globe at an alarming rate (1-3), and climate change now figures prominently as a potential interactive driver of some of these declines (4-6). A shift to earlier breeding phenology has been documented in a number of species (7-11), but this shift is not universal across species and has not been tied to population-level consequences. Other work has associated climatic conditions with disease-related declines in the Neotropics (4, 5), yet no mechanisms have been definitively linked to these correlations (12, 13). Reading et al. (14) showed a decrease in adult female body condition and survival in a population of common toads (Bufo bufo) that corresponded with an increase in average annual temperatures. However, these demographic changes were not explicitly linked to changes in population size over time. Kiesecker et al. (15) showed that disease, UV-B, and climate change could interact to increase embryo mortality in western toad (Bufo boreas) populations, yet these populations have not declined. This increased premetamorphic mortality may not be sufficient to cause otherwise increasing populations to decline in the long term. Alternatively, it may be that conditions in short-term or laboratory-based studies are not always representative of long-term patterns in natural populations. To determine mechanisms of population change, we first need to know which vital rates are affected by changes in climate, and then how these changes affect population dynamics.The effects of climate change on growth and survival are particularly relev...

The bull trout Salvelinus confluentus is listed as a federally threatened species in the Columbia and Klamath river drainages. A priori establishment of levels of decline or increase in bull trout redd numbers that will be considered biologically significant and levels of statistical significance that will be used to identify changes in redd numbers is essential to the success of future recovery plans. A prospective statistical power analysis indicates that with standard significance levels and two-tailed testing procedures the yearly variation in redd numbers typifying many stocks of bull trout in Montana limits the power of detecting less than 50% of changes in population size per generation to less than 0.8 during the first 15 years of a monitoring program. The limitations of monitoring bull trout stocks with redd counts, coupled with the critical nature of identifying future population changes, justifies the need to (1) identify and reduce the level of measurement error involved in redd counts, (2) use levels of statistical significance that adequately balance the risks of committing type I and type II errors, (3) use one-tailed testing procedures for identifying population declines during the initial and other critical years of a monitoring program, and (4) explore the use of other methods of monitoring.

Aim  The introduction of non‐native species into aquatic environments has been linked with local extinctions and altered distributions of native species. We investigated the effect of non‐native salmonids on the occupancy of two native amphibians, the long‐toed salamander (Ambystoma macrodactylum) and Columbia spotted frog (Rana luteiventris), across three spatial scales: water bodies, small catchments and large catchments.Location  Mountain lakes at ≥ 1500 m elevation were surveyed across the northern Rocky Mountains, USA.Methods  We surveyed 2267 water bodies for amphibian occupancy (based on evidence of reproduction) and fish presence between 1986 and 2002 and modelled the probability of amphibian occupancy at each spatial scale in relation to habitat availability and quality and fish presence.Results  After accounting for habitat features, we estimated that A. macrodactylum was 2.3 times more likely to breed in fishless water bodies than in water bodies with fish. Ambystoma macrodactylum also was more likely to occupy small catchments where none of the water bodies contained fish than in catchments where at least one water body contained fish. However, the probability of salamander occupancy in small catchments was also influenced by habitat availability (i.e. the number of water bodies within a catchment) and suitability of remaining fishless water bodies. We found no relationship between fish presence and salamander occupancy at the large‐catchment scale, probably because of increased habitat availability. In contrast to A. macrodactylum, we found no relationship between fish presence and R. luteiventris occupancy at any scale.Main conclusions  Our results suggest that the negative effects of non‐native salmonids can extend beyond the boundaries of individual water bodies and increase A. macrodactylum extinction risk at landscape scales. We suspect that niche overlap between non‐native fish and A. macrodactylum at higher elevations in the northern Rocky Mountains may lead to extinction in catchments with limited suitable habitat.