A Resistant-Kernel Model of Connectivity for Amphibians that Breed in Vernal Pools

Abstract:  Pool-breeding amphibian populations operate at multiple scales, from the individual pool to surrounding upland habitat to clusters of pools. When metapopulation dynamics play a role in long-term viability, conservation efforts limited to the protection of individual pools or even pools with associated upland habitat may be ineffective over the long term if connectivity among pools is not maintained. Connectivity becomes especially important and difficult to assess in regions where suburban sprawl is rapidly increasing land development, road density, and traffic rates. We developed a model of connectivity among vernal pools for the four ambystomatid salamanders that occur in Massachusetts and applied it to the nearly 30,000 potential ephemeral wetlands across the state. The model was based on a modification of the kernel estimator (a density estimator commonly used in home range studies) that takes landscape resistance into account. The model was parameterized with empirical migration distances for spotted salamanders ( Ambystoma maculatum ), dispersal distances for marbled salamanders ( A. opacum ), and expert-derived estimates of landscape resistance. The model ranked vernal pools in Massachusetts by local, neighborhood, and regional connectivity and by an integrated measure of connectivity, both statewide and within ecoregions. The most functionally connected pool complexes occurred in southeastern and northeastern Massachusetts, areas with rapidly increasing suburban development. In a sensitivity analysis estimates of pool connectivity were relatively insensitive to uncertainty in parameter estimates, especially at the local and neighborhood scales. Our connectivity model could be used to prioritize conservation efforts for vernal-pool amphibian populations at broader scales than traditional pool-based approaches.     

中国林蛙Rana chensinensis遗传多样性初步研究

用寡聚核苷酸探针ＬＺＦ－１，对中国林蛙的基因指纹进行了研究，结果表明，中国林蛙３个居群扔Ｈｉｎｆ－１酶切片段的ＤＮＡ指纹图呈现在个体水平，群居水平和物种水平的高度多态性。     

Habitat Suitability Models and the Shortfall in Conservation Planning for African Vertebrates

Abstract:  Ongoing loss of biodiversity requires identifying large-scale conservation priorities, but the detailed information on the distribution of species required for this purpose is often missing. We present a systematic reserve selection for 1223 African mammals and amphibians in which habitat suitability models are used as estimates of the area occupied by species. In the framework of the World Conservation Union (IUCN) Global Amphibian Assessment and IUCN Global Mammal Assessment, we collected the geographic range (extent of occurrence) and habitat preferences for each species. We used the latter to build species-specific habitat suitability models inside geographic ranges, and for 181 species we verified the models by comparing suitability levels to presence-absence data collected in the field. We then used the suitable areas as estimators of the area of occupancy and compared the results of systematic reserve selection based on geographic ranges to those based on estimated areas of occupancy. Our results showed that the reserve system would need a 30-100% expansion to achieve minimal conservation targets, concentrated in the tropics, where species richness reaches a maximum. Comparative analyses revealed that using geographic ranges, which overestimate the area occupied by species, underestimates the total amount of area that needs to be conserved. The area selected for conservation doubled when we used the estimated area of occupancy in place of the geographic ranges. This happened because the suitable areas potentially occupied by each species overlapped less than their geographic ranges. As a result, any given protected area contained fewer species than predicted by the analysis of ranges. Because species are more specialized than our estimates of distribution based on extent of occurrence suggest, we propose that this is a general effect in systematic conservation planning.     

Safeguarding Wetlands and Their Connections within Wetlandscapes to Improve Conservation Outcomes for Threatened Amphibian Species

Wetlands should not be considered as independent objects but as dynamically connected objects, collectively known as wetlandscapes. We developed a framework that analyzes the influences of wetland suitability and connectivity on amphibian distributions. We defined two indices: a Wetland Suitability Index describing wetland quality and a Movement Permeability Index characterizing wetland connectivity for amphibian population dynamics. These indices were calculated from raster datasets and time‐varying inundation estimates. The indices were used to define a wetlandscape and an amphibian model was used to simulate population dynamics within the wetlandscape. The framework was applied to the Nose Creek watershed, a highly modified wetlandscape in Alberta, Canada. Two amphibian species were selected with different habitat preferences: the Northern Leopard Frog that prefers wet habitats and has high mobility over land, and the Great Plains Toad that prefers terrestrial habitats and has low mobility over land. We found each amphibian species had a “preferred” wetlandscape, reflecting their life cycle traits and migration strategies which in turn were dependent on the hydrological and ecological connections within the wetlandscape. This study highlights the importance of investigating both individual wetlands and the wetlandscape and considering both wetland habitat quality and connectivity as non‐substitutable properties that act jointly, but differently, on population dynamics.     

Cost‐effective conservation of an endangered frog under uncertainty

How should managers choose among conservation options when resources are scarce and there is uncertainty regarding the effectiveness of actions? Well‐developed tools exist for prioritizing areas for one‐time and binary actions (e.g., protect vs. not protect), but methods for prioritizing incremental or ongoing actions (such as habitat creation and maintenance) remain uncommon. We devised an approach that combines metapopulation viability and cost‐effectiveness analyses to select among alternative conservation actions while accounting for uncertainty. In our study, cost‐effectiveness is the ratio between the benefit of an action and its economic cost, where benefit is the change in metapopulation viability. We applied the approach to the case of the endangered growling grass frog (Litoria raniformis), which is threatened by urban development. We extended a Bayesian model to predict metapopulation viability under 9 urbanization and management scenarios and incorporated the full probability distribution of possible outcomes for each scenario into the cost‐effectiveness analysis. This allowed us to discern between cost‐effective alternatives that were robust to uncertainty and those with a relatively high risk of failure. We found a relatively high risk of extinction following urbanization if the only action was reservation of core habitat; habitat creation actions performed better than enhancement actions; and cost‐effectiveness ranking changed depending on the consideration of uncertainty. Our results suggest that creation and maintenance of wetlands dedicated to L. raniformis is the only cost‐effective action likely to result in a sufficiently low risk of extinction. To our knowledge we are the first study to use Bayesian metapopulation viability analysis to explicitly incorporate parametric and demographic uncertainty into a cost‐effective evaluation of conservation actions. The approach offers guidance to decision makers aiming to achieve cost‐effective conservation under uncertainty.     

Assessing Changes in Amphibian Population Dynamics Following Experimental Manipulations of Introduced Fish

Abstract: Sport‐fish introductions are now recognized as an important cause of amphibian decline, but few researchers have quantified the demographic responses of amphibians to current options in fisheries management designed to minimize effects on sensitive amphibians. Demographic analyses with mark–recapture data allow researchers to assess the relative importance of survival, local recruitment, and migration to changes in population densities. I conducted a 4‐year, replicated whole‐lake experiment in the Klamath Mountains of northern California (U.S.A.) to quantify changes in population density, survival, population growth rate, and recruitment of the Cascades frog (Rana cascadae) in response to manipulations of non‐native fish populations. I compared responses of the frogs in lakes where fish were removed, in lakes in their naturally fish‐free state, and in lakes where fish remained that were either stocked annually or no longer being stocked. Within 3 years of fish removals from 3 lakes, frog densities increased by a factor of 13.6. The survival of young adult frogs increased from 59% to 94%, and realized population growth and recruitment rates at the fish‐removal lakes were more than twice as high as the rates for fish‐free reference lakes and lakes that contained fish. Population growth in the fish‐removal lakes was likely due to better on‐site recruitment of frogs to later life stages rather than increased immigration. The effects on R. cascadae of suspending stocking were ambiguous and suggested no direct benefit to amphibians. With amphibians declining worldwide, these results show that active restoration can slow or reverse the decline of species affected by fish stocking within a short time frame.     

Calculating Biologically Accurate Mitigation Credits: Insights from the California Tiger Salamander

Abstract:  Current conservation mitigation plans often fail to ensure full in-kind habitat replacement for endangered species, which suggests the need for improved methods for calculating mitigation credits. A simple, yet biologically meaningful method for calculating mitigation credits would be to let the number of mitigation credits assigned to a parcel of land scale with the reproductive value of the individuals occupying that parcel. This can be accomplished by dividing the population into 2 or more subdivisions with different reproductive values, calculating the densities of these subdivisions as a function of one or more habitat parameters, and then forming a weighted sum of these densities such that each density distribution is weighted by the reproductive value of its respective subdivision of the population. This weighted sum is the density distribution of reproductive value, and by integrating it over a particular parcel, one can determine the mitigation value of that parcel. We carried out this procedure for a population of California tiger salamanders ( Ambystoma californiense ), with distance from breeding site as our habitat parameter and the 3 visually identifiable age classes (adults, juveniles, and metamorphs) as our population subdivisions. This led to a density distribution of reproductive value that decreased exponentially with increasing distance from a breeding site. Mitigation strategies derived from this function will be more likely to ensure the persistence of California tiger salamander populations than current approaches, which assign all land within 1.6 km of a breeding site the same mitigation value. Use of the density distribution of reproductive value as a basis for mitigation plans is a procedure that can be applied to all endangered species, and it should improve the quality of mitigation decisions.     

Identifying Habitat Variables Important to the Rare Columbia Spotted Frog in Utah (U.S.A.): an Information-Theoretic Approach

Abstract:  We identified habitat associations of the rare Columbia spotted frog (  Rana luteiventris ). We used an information-theoretic approach that encouraged careful consideration of previous studies, demanded a priori formulation of hypotheses and models, and provided interpretable results while avoiding some criticisms of traditional statistical analyses. We formulated hypotheses about habitat associations based on conductivity, emergent vegetation, littoral zone depth, pond hydrology, and water temperature. We modeled hypothesized associations with logistic regression and used Akaike's information criterion to quantify evidence for models, weigh the relative importance of each habitat variable, and select predictive models. Although variable, results suggested that spotted frogs are more likely to occur in ponds that do not shrink in size seasonally, maintain relatively constant seasonal water temperature, and have high emergent vegetation cover. Associations we identified will assist actions in Utah that may be critical to local persistence of spotted frogs. Moreover, this approach for identifying associations has great potential for other rare species.     

Chytridiomycosis and Seasonal Mortality of Tropical Stream‐Associated Frogs 15 Years after Introduction of Batrachochytrium dendrobatidis

Assessing the effects of diseases on wildlife populations can be difficult in the absence of observed mortalities, but it is crucial for threat assessment and conservation. We performed an intensive capture‐mark‐recapture study across seasons and years to investigate the effect of chytridiomycosis on demographics in 2 populations of the threatened common mist frog (Litoria rheocola) in the lowland wet tropics of Queensland, Australia. Infection prevalence was the best predictor for apparent survival probability in adult males and varied widely with season (0–65%). Infection prevalence was highest in winter months when monthly survival probabilities were low (approximately 70%). Populations at both sites exhibited very low annual survival probabilities (12–15%) but high recruitment (71–91%), which resulted in population growth rates that fluctuated seasonally. Our results suggest that even in the absence of observed mortalities and continued declines, and despite host–pathogen co‐existence for multiple host generations over almost 2 decades, chytridiomycosis continues to have substantial seasonally fluctuating population‐level effects on amphibian survival, which necessitates increased recruitment for population persistence. Similarly infected populations may thus be under continued threat from chytridiomycosis which may render them vulnerable to other threatening processes, particularly those affecting recruitment success. Quitridiomicosis y Mortalidad Estacional de Ranas Asociadas a Arroyos Tropicales Quince Años Después de la Introducción de Batrachochytrium dendrobatidisvsp     

上海郊区三类典型生境的两栖类分布特征

上海郊区农田,林地,湿地(池塘)三类典型生境是两栖类最主要的栖息地,生境的差异以及两栖类生态特征的不同造成了两栖类在分布上的差异。2014年和2016年5~8月对上海郊区三类典型生境的30个研究样点两栖类生物多样性进行调查,并运用单因素方差分析对三类生境的两栖类群落结构进行比较,通过层次聚类法分析不同生境的两栖类组成相似性。结果显示:(1)两年间共记录到上海郊区两栖类动物1目4科4属5种5 397只,其中泽陆蛙(Fejervarya multistriata),金线侧褶蛙(Pelophylax plancyi)为优势种。黑斑侧褶蛙(Pelophylax nigromaculata),中华蟾蜍(Bufo gargarizans),饰纹姬蛙(Microhyla fissipes)为常见种。这5种两栖类都为广型分布种。(2)三类生境的两栖类物种丰富度无显著性差异,而两栖类多度差异显著。(3)泽陆蛙,饰纹姬蛙的种群密度在三类生境中差异显著,且在农田生境中最高。黑斑侧褶蛙,金线侧褶蛙的种群密度在三类生境中差异显著且在池塘生境中最高。中华蟾蜍在三类生境中的种群密度无显著性差异。(4)聚类结果为30个研究样点中林地生境与池塘生境被聚为一类,农田生境被单独聚为一类。建议通过对不同生境的保护与恢复达到对上海郊区两栖类生物多样性保护的目的。