Search ARMI Database

Maintenance of genetic diversity at adaptive loci may facilitate invasions by non-native species by allowing populations to adapt to novel environments, despite the loss of diversity at neutral loci that typically occurs during founder events. To evaluate this prediction, we compared genetic diversity at major histocompatibility complex (MHC) and cytochrome b (cytb) loci from 20 populations of the American bullfrog (Rana catesbeiana) across the invasive and native ranges in North America and quantified the presence of the pathogen Batrachochytrium dendrobatidis (Bd). Compared to native populations, invasive populations had significantly higher Bd prevalence and intensity, significantly higher pairwise MHC and cytb FST, and significantly lower cytb diversity, but maintained similar levels of MHC diversity. The two most common MHC alleles (LiCA_B and Rapi_33) were associated with a significant decreased risk of Bd infection, and we detected positive selection acting on four peptide binding residues. Phylogenetic analysis suggested invasive populations likely arose from a single founding population in the American Midwest with a possible subsequent invasion in the northwest. Overall, our study suggests that the maintenance of diversity at adaptive loci may contribute to invasion success and highlights the importance of quantifying diversity at functional loci to assess the evolutionary potential of invasive populations.

Protected areas like national parks are essential elements of conservation because they limit human influence on the landscape, which protects biodiversity and ecosystem function. The role of national parks in conservation, however, often goes far beyond limiting human influence. The U.S. National Park Service and its system of land units contribute substantively to conservation by providing protected lands where researchers can document trends in species distributions and abundances, examine characteristics important for generating these trends, and identify and implement conservation strategies to preserve biodiversity. We reviewed the contribution of U.S. national parks to amphibian research and conservation and highlight important challenges and findings in several key areas. First, U.S. national parks were instrumental in providing strong support that amphibian declines were real and unlikely to be simply a consequence of habitat loss. Second, research in U.S. national parks provided evidence against certain hypothesized causes of decline, like UV-B radiation, and evidence for others, such as introduced species and disease. However, describing declines and identifying causes contributes to conservation only if it leads to management; importantly, U.S. national parks have implemented many conservation strategies and evaluated their effectiveness in recovering robust amphibian populations. Among these, removal of invasive species, especially fishes; conservation translocations; and habitat creation and enhancement stand out as examples of successful conservation strategies with broad applicability. Successful management for amphibians is additionally complicated by competing mandates and stakeholder interests; for example, past emphasis on increasing visitor enjoyment by introducing fish to formerly fishless lakes had devastating consequences for many amphibians. Other potential conflicts with amphibian conservation include increasing development, increased risk of introductions of disease and exotic species with increased visitation, and road mortality. Decision science and leveraging partnerships have proven to be key components of effective conservation under conflicting mandates in national parks. As resource managers grapple with large-scale drivers that are outside local control, public-private partnerships and adaptive strategies are increasing in importance. U.S. national parks have played an important role in many aspects of identifying and ameliorating the amphibian decline crisis and will continue to be essential for the conservation of amphibians in the future.

1. The increasing frequency and severity of drought has the potential to exacerbate existing global amphibian declines. However, interactions between drought and coincident stressors, coupled with high interannual variability in amphibian abundances, can mask the extent and underlying mechanisms of drought-induced declines. The application of dynamic occupancy modeling to longitudinal monitoring data estimates the effect of specific variables on population change, providing key insights into potential management strategies for drought resilience.
2. We synthesized a decade (2009 – 2019) of amphibian survey data from multiple monitoring programs across the California Bay Area and used occupancy modeling to estimate the influence of drought, invasive species, and land use on species’ persistence and colonization probabilities. The geographic and temporal scale of our dataset, consisting of 2574 surveys of seven species in 473 ponds, allowed us to quantify regional trends for an entire community of pond-breeding amphibians.
3. An extreme drought from 2012 – 2015 resulted in losses of breeding sites, with 51% of ponds drying in 2014 compared to <10% in non-drought years. Pond drying reduced persistence rates, and nearly every species exhibited reduced occupancy during the drought, with some species (American bullfrogs and California newts) declining by > 25%. Drought reduced occupancy via additional mechanisms beyond habitat loss; for example, lower spring precipitation (an important cue for breeding) was associated with reduced colonization.
4. During drought, native species’ persistence was higher in permanent relative to temporary ponds, even though these sites were also more likely to contain invasive fish and bullfrogs, which generally reduced native amphibian occupancy. Many of these permanent ponds dried during the worst year of drought, leading to extirpations of invasive species that appeared long-lasting. In contrast, native species rebounded quickly with returning rains and showed evidence of full recovery.
5. Synthesis and applications: Despite experiencing one of most severe droughts in a millennium, native species displayed high resilience. Due to longer recovery times by non-native relative to native species, drought presents a valuable management opportunity to remove invaders from key refugia, and we highlight the value of maintaining hydroperiod diversity to promote the persistence of multiple species.

Introduced species often disrupt established food webs, but some native predators can come to rely on introduced prey. Understanding the net effects of the non-natives on imperiled predators is crucial for planning conservation measures. The invasive American bullfrog (Lithobates catesbeianus) can be prey, predator, and competitor for the critically endangered San Francisco garter snake (Thamnophis sirtalis tetrataenia). We examined the seasonal prey use of a San Francisco garter snake population that co-occurs with American bullfrogs to examine intraguild predation between these species. Juvenile and adult snakes mainly consumed native anurans instead of American bullfrogs, and this diet pattern peaked in spring, a critical foraging period for the snakes. In spring, large adult American bullfrogs also foraged heavily on native anurans and displayed a high degree of diet overlap with San Francisco garter snakes. Invasive American bullfrogs are detrimental to San Francisco garter snakes mainly through seasonal competition rather than reciprocal predation. Removal of invasive species provided further evidence that eliminating American bullfrogs can benefit San Francisco garter snakes by reducing predation pressure on their shared amphibian prey. Better understanding the interactions of invasive species with native species of conservation concern informs management practices and improves conservation outcomes.

Background. The southern California biodiversity hotspot has had a complex geological history, with both plate tectonic forces and sea level changes repeatedly reconfiguring the region, and likely driving both lineage splittings and extinctions. Here we investigate patterns of genetic divergence in two species of slender salamanders (Plethodontidae: Batrachoseps) in this region. The complex geological history in combination with several organismal traits led us to predict that these species harbor multiple ancient mitochondrial lineages endemic to southern California. These species belong to a clade characterized by fine-scale mitochondrial structure, which has been shown to track ancient splits. Both focal species, Batrachoseps major and B. nigriventris, are relatively widely distributed in southern California, and estimated to have persisted there across millions of years. Recently several extralimital populations of Batrachoseps were found in the San Joaquin Valley of California, a former desert area that has been extensively modified for agriculture. The origins of these populations are unknown, but based on morphology, they are hypothesized to result from human-mediated introductions of B. major.
Methods. We sequenced the mitochondrial gene cytochrome b from a geographically comprehensive sampling of the mitochondrial lineages of B. major and B. nigriventris that are endemic to southern California. We used phylogenetic analyses to characterize phylogeographic structure and identify mitochondrial contact zones. We also included the San Joaquin Valley samples to test whether they resulted from introductions. We used a bootstrap resampling approach to compare the strength of isolation-by-distance in both Batrachoseps species and four other salamander species with which they co-occur in southern California.
Results. The northern lineage of B. major harbors at least eight deeply differentiated, geographically cohesive mitochondrial subclades. We identify geographic contact between many of these mtDNA lineages and some biogeographic features that are concordant with lineage boundaries. Batrachoseps nigriventris also has multiple deeply differentiated clades within the region. Comparative analyses highlight the smaller spatial scales over which mitochondrial divergence accumulates in Batrachoseps relative to most other salamander species in southern California. The extralimital populations of Batrachoseps from the San Joaquin Valley are assigned to B. major based on their mitochondrial haplotypes and are shown to result from at least two independent introductions from different source populations. We also suggest that B. major on Catalina Island, where it is considered native, may be the result of an introduction. Some of the same traits that facilitate the build-up of deep phylogeographic structure in Batrachoseps likely also contribute to its propensity for introductions, and we anticipate that additional introduced populations will be discovered.

A note on the geographic distribution of the Cuban Treefrog (Osteopilus septentrionalis), describing new parish records in East Baton Rouge Parish and Lafayette Parish.

The western pond turtle (WPT), recently separated into two paripatrically distributed species (Emys pallida and Emys marmorata), is experiencing significant reductions in its range and population size. In addition to habitat loss, two potential causes of decline are female-biased road mortality and high juvenile mortality from non-native predatory bullfrogs (Rana catesbeiana). However, quantitative analyses of these threats have never been conducted for either species of WPT. We used a combination of historical museum samples and published and unpublished field studies shared with us through personal communications with WPT field researchers (B Shaffer, P Scott, R Fisher, C Brown, R Dagit, L Patterson, T Engstrom, 2019, personal communications) to quantify the effect of roads and bullfrogs on WPT populations along the west coast of the United States. Both species of WPT shift toward increasingly male biased museum collections over the last century, a trend consistent with increasing, female-biased road mortality. Recent WPT population studies revealed that road density and proximity were significantly associated with increasingly male-biased sex ratios, further suggesting female-biased road mortality. The mean body size of museum collections of E. marmorata, but not E. pallida, has increased over the last 100 years, consistent with reduced recruitment and aging populations that could be driven by invasive predators. Contemporary WPT population sites that co-occur with bullfrogs had significantly greater average body sizes than population sites without bullfrogs, suggesting strong bullfrog predation on small WPT hatchlings and juveniles. Overall, our findings indicate that both species of WPT face demographic challenges which would have been difficult to document without the use of both historical data from natural history collections and contemporary demographic field data. Although correlational, our analyses suggest that female-biased road mortality and predation on small turtles by non-native bullfrogs are occurring, and that conservation strategies reducing both may be important for WPT recovery.

A note on the geographic distribution of the Cuban Treefrog (Osteopilus septentrionalis), describing new parish records in St. Tammany Parish and Orleans Parish.

A note on the geographic distribution of the Cuban Treefrog (Osteopilus septentrionalis), describing a new parish record and probable establishment in St. Charles Parish.

We used five years of capture mark-recapture data to estimate annual apparent survival of post-metamorphic bullfrogs in a population on the Buenos Aires National Wildlife Refuge in their invaded range in Arizona, U.S.A.

Conservation of at-risk species is aided by reliable forecasts of the consequences of environmental change and management actions on population viability. Forecasts from conventional population viability analysis (PVA) are made using a two-step procedure in which parameters are estimated, or elicited from expert opinion, and then plugged into a stochastic population model without accounting for parameter uncertainty. Recently-developed statistical PVAs differ because forecasts are made conditional on models that are fitted to empirical data. The statistical forecasting approach allows for uncertainty about parameters, but it has rarely been applied in metapopulation contexts where spatially-explicit inference is needed about colonization and extinction dynamics and other forms of stochasticity that influence metapopulation viability. We conducted a statistical metapopulation viability analysis (MPVA) using 11 years of data on the federally-threatened Chiricahua leopard frog to forecast responses to landscape heterogeneity, drought, environmental stochasticity, and management. We evaluated several future environmental scenarios and pond restoration options designed to reduce extinction risk. Forecasts over a 50-yr time horizon indicated that metapopulation extinction risk was <8% for all scenarios, but uncertainty was high. Without pond restoration, extinction risk is forecasted to be 5.6% (95% CI: 0?60%) by year 2060. Restoring six ponds by increasing hydroperiod reduced extinction risk to 1.0% (0 ? 11%) in year 2060. We found little evidence that drought influences metapopulation viability when managers have the ability to maintain ponds that hold water throughout the year and are free of invasive species. Our study illustrates the utility of the spatially explicit statistical forecasting approach to MPVA in conservation planning efforts.

Invasive species are a major threat to the persistence of native species, particularly in systems where ephemeral aquatic habitats have been converted to or replaced by permanent water and predators such as fish have been introduced. Within the Altar Valley, Arizona, USA, the invasive American bullfrog (Lithobates [=Rana] catesbeianus) has been successfully eradicated to help recover Chiricahua leopard frogs (Lithobates chiricahuensis). However, other non-native predators including sunfish (Lepomis spp) are present in some permanent water bodies. During four consecutive years (2014-2017) we detected both the federally-threatened Chiricahua leopard frog and sunfish at one permanent water body in the Altar Valley. This suggests that despite the potential negative effect of predatory fish on amphibians, there may be conditions where the Chiricahua leopard frog may be able to co-occur with this non-native predator. A better understanding of rare situations of co-occurrence with non-native predators may contribute to our understanding of why co-occurrence happens in some but not all systems and whether conservation strategies can be developed in situations where complete eradication of non-native predators is infeasible.

The introductions of non-native predators often reduce biodiversity and affect natural predator-prey relationships. However, non-native predators may increase the abundance of potential disease vectors (e.g. mosquitoes) indirectly through competition or predation cascades. The Santa Monica
Mountains, situated in a global biodiversity hotspot, is an area of conservation concern due to climate change, urbanization, and the introduction of non-native species. We examined the effect that non-native crayfish (Procambarus clarkii) have on an existing native predator, dragonfly nymphs (Aeshna sp.) and their mosquito larvae (Anopheles sp.) prey. We used laboratory experiments to compare the predation efficiency of both predators, separately and together, and field data on counts of dragonfly nymphs and mosquito larvae sampled from 13 local streams. We predicted a lower predation efficiency of crayfish compared to native dragonfly nymphs as well as a reduced efficiency of dragonfly nymphs in the presence of crayfish. Dragonfly nymphs were an order of magnitude more efficient mosquito predators compared to crayfish and dragonfly
nymphs suffered reduced efficiency in the presence of crayfish. Analyses of field count data showed that populations of dragonfly nymphs and mosquito larvae were strongly correlated with crayfish presence in streams, such that sites with crayfish tended to have fewer dragonfly
nymphs and more mosquito larvae. Under natural conditions, it is likely that crayfish reduce the abundance of dragonfly nymphs and their predation efficiency, and thereby, directly and indirectly, lead to higher mosquito populations and a loss of ecosystem services related to disease vector control.

The Cuban treefrog, Osteopilus septentrionalis, is native to Cuba, the Bahamas, and the Cayman Islands, and is invasive in areas where it has been introduced and established in the Caribbean as well as Hawaii and Florida. Despite repeated occurrences in several states over many years, it was not believed that Cuban treefrogs had successfully established outside of Florida in the mainland United States. From mid-September to mid-November 2017, we captured and removed 367 Cuban treefrogs in just four surveys in New Orleans, Louisiana. The impacts of this population on native treefrogs in this area is unknown but possibly severe as indicated by the paucity of observations of native treefrogs during our surveys. Eradication of this seemingly established population is improbable, but continued surveys will facilitate learning about the ecology and genetics of this novel population.

Chytridiomycosis is caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) and is regarded as one of the most significant threats to global amphibian populations. In M?xico, Bd was first reported in 2003 and has now been documented in 13 states. We visited 33 localities and swabbed 199 wild-caught anurans from seven species (five native, two exotic) across the Mediterranean region of the state of Baja California. Using quantitative PCR, Bd was detected in 94 individuals (47.2% of samples) at 25 of the 33 survey localities for five native and one exotic frog species. Only the non-native Xenopus laevis tested negative for Bd. We found significant differences between mean Bd loads of different species, and that remoteness and distance to agricultural land were the best positive predictors of Bd prevalence. These are the first Bd-positive results for the state of Baja California and its presence should be regarded as an additional conservation threat to the region?s native frog species.

In North America, ranid frogs (Ranidae) have experienced larger declines than any other amphibian family, particularly species native to the southwestern USA and adjacent Mexico; however, our knowledge of their conservation status and threats is limited in Mexico. We assessed the status of the federally-threatened (USA) Chiricahua Leopard Frog (Lithobates chiricahuensis) in Sonora, Mexico, based on a search of museum specimens, published records, unpublished accounts, and surveys of 84 sites within the geographical and elevational range of the species from 2000-2016. We also provide information on occurrence of three other native ranid frog species encountered opportunistically during our surveys. The Chiricahua Leopard Frog is known in Sonora from only 20 historical (pre-2000) localities. Searches of three historical sites from 2000-2016 did not reveal any Chiricahua Leopard Frogs; however, we found it at three previously undocumented sites in 2016, all near Cananea. To our knowledge, these records are the first observations of Chiricahua Leopard Frogs in Sonora since 1998. Differences in conservation status between the USA and Sonora are likely due to differing magnitude and distribution of threats and a comparatively aggressive recovery program in the USA. For example, key non-native predators important in the decline of the Chiricahua Leopard Frog are much less widespread in Sonora compared to the USA Southwest, but there are fewer protections and recovery actions for the frog in Sonora than in the USA. Additional surveys for the Chiricahua Leopard Frog and other amphibians in Sonora should be a priority to fully assess threats and conservation status.

Understanding the additive or interactive threats of habitat transformation and invasive species is critical for conservation, especially where climate change is expected to increase the severity or frequency of drought. In the arid southwestern USA, this combination of stressors has caused widespread declines of native aquatic and semi-aquatic species. Achieving resilience to drought and other effects of climate change may depend upon continued management, so understanding the combined effects of stressors is important. We used Bayesian hierarchical models fitted with 10-yrs of pond-based monitoring surveys for the federally-endangered Sonoran Tiger Salamander (Ambystoma mavortium stebbinsi) and invasive predators (fishes and American Bullfrogs, Lithobates catesbeianus) that threaten native species. We estimated trends in occupancy of salamanders and invasive predators while accounting for hydrological dynamics of ponds, then used a two-species interaction model to directly estimate how invasive predators affected salamander occupancy. We also tested a conceptual model that predicted that drought, by limiting the distribution of invasive predators, could ultimately benefit native species. Even though occupancy of invasive predators was stationary and their presence in a pond reduced the probability of salamander presence by 23%, occupancy of Sonoran Tiger Salamanders increased, annually, by 2.2%. Occupancy of salamanders and invasive predators both declined dramatically following the 5th consecutive year of drought. Salamander occupancy recovered quickly after return to non-drought conditions, while occupancy of invasive predators remained suppressed. Models that incorporated three time-lagged periods (1 to 4 yrs) of local moisture conditions confirmed that salamanders and invasive predators responded differently to drought, reflecting how life-history strategies shape responses to disturbances. The positive 10-yr trend in salamander occupancy and their rapid recovery after drought provided partial support for the hypothesis of drought-mediated coexistence with invasive predators. These results also suggest management opportunities for conservation of the Sonoran Tiger Salamander and other imperiled organisms in human-transformed landscapes.

California Red-legged Frogs (Rana draytonii) are typically regarded as inhabitants of permanent ponds, marshes, and slow-moving streams, but their ecology in other habitats, such as drainages among coastal dunes, remains obscure. Because coastal dune ecosystems have been degraded by development, off-highway vehicle use, stabilization, and invasive species, these unique ecosystems are the focus of restoration efforts. To better understand the ecology of California Red-legged Frogs in coastal dune ecosystems and to avoid and minimize potential negative effects of dune restoration activities on these rare frogs, we studied their spatial ecology, habitat selection, and survival in coastal dune drainages at Point Reyes National Seashore, California, USA. All 22 radio-marked frogs remained in their home drainages throughout the spring and summer of 2015 and, with some notable exceptions, most remained close to water. Local convex hull home ranges of four out of five California Red-legged Frogs with > 20 observations in dunes were < 1,600 m2. At the population level, frogs were 1.7 (1.2-4.4) times more likely to select sites 1 m closer to water, and were 83 (2.0-17,000) times more likely to select sites with 10% greater percent cover of logs that served as refuges from environmental extremes and predators. On average, California Red-legged Frogs avoided the invasive plants Iceplant (Carpobrotus edulis) and European Beachgrass (Ammophila arenaria). Frogs were https://0.68 (0.32-0.89) and https://0.55 (0.24-0.75) times as likely to select areas that had 10% greater cover of these plants, respectively. Assuming constant risk of mortality, California Red-legged Frogs had an annual survival rate of https://0.70 (range, 0.27-0.96) in coastal dune drainages. This relatively high survival rate suggests that coastal dune drainages provide a locally important habitat for California Red-legged Frogs. Restoration practices that maintain wetted drainages with logjams are likely to benefit California Red-legged Frogs.