Population Size Influences Amphibian Detection Probability: Implications for Biodiversity Monitoring Programs

Monitoring is an integral part of species conservation. Monitoring programs must take imperfect detection of species into account in order to be reliable. Theory suggests that detection probability may be determined by population size but this relationship has not yet been assessed empirically. Population size is particularly important because it may induce heterogeneity in detection probability and thereby cause bias in estimates of biodiversity. We used a site occupancy model to analyse data from a volunteer-based amphibian monitoring program to assess how well different variables explain variation in detection probability. An index to population size best explained detection probabilities for four out of six species (to avoid circular reasoning, we used the count of individuals at a previous site visit as an index to current population size). The relationship between the population index and detection probability was positive. Commonly used weather variables best explained detection probabilities for two out of six species. Estimates of site occupancy probabilities differed depending on whether the population index was or was not used to model detection probability. The relationship between the population index and detectability has implications for the design of monitoring and species conservation. Most importantly, because many small populations are likely to be overlooked, monitoring programs should be designed in such a way that small populations are not overlooked. The results also imply that methods cannot be standardized in such a way that detection probabilities are constant. As we have shown here, one can easily account for variation in population size in the analysis of data from long-term monitoring programs by using counts of individuals from surveys at the same site in previous years. Accounting for variation in population size is important because it can affect the results of long-term monitoring programs and ultimately the conservation of imperiled species

Apparent survival of the salamander Salamandra salamandra is low because of high migratory activity

BACKGROUND: Understanding the demographic processes underlying population dynamics is a central theme in ecology. Populations decline if losses from the population (i.e., mortality and emigration) exceed gains (i.e., recruitment and immigration). Amphibians are thought to exhibit little movement even though local populations often fluctuate dramatically and are likely to go exinct if there is no rescue effect through immigration from nearby populations. Terrestrial salamanders are generally portrayed as amphibians with low migratory activity. Our study uses demographic analysis as a key to unravel whether emigration or mortality is the main cause of "losses" from the population. In particular, we use the analysis to challenge the common belief that terrestrial salamanders show low migratory activity. RESULTS: The mark-recapture analysis of adult salamanders showed that monthly survival was high (> 90%) without a seasonal pattern. These estimates, however, translate into rather low rates of local annual survival of only ~40% and suggest that emigration was important. The estimated probability of emigration was 49%. CONCLUSION: Our analysis shows that terrestrial salamanders exhibit more migratory activity than commonly thought. This may be due either because the spatial extent of salamander populations is underestimated or because there is a substantial exchange of individuals between populations. Our current results are in line with several other studies that suggest high migratory activity in amphibians. In particular, many amphibian populations may be characterized by high proportions of transients and/or floaters

Large-Scale Statistical Learning for Mass Transport Prediction in Porous Materials Using 90,000 Artificially Generated Microstructures

Effective properties of functional materials crucially depend on their 3D microstructure. In this paper, we investigate quantitative relationships between descriptors of two-phase microstructures, consisting of solid and pores and their mass transport properties. To that end, we generate a vast database comprising 90,000 microstructures drawn from nine different stochastic models, and compute their effective diffusivity and permeability as well as various microstructural descriptors. To the best of our knowledge, this is the largest and most diverse dataset created for studying the influence of 3D microstructure on mass transport. In particular, we establish microstructure-property relationships using analytical prediction formulas, artificial (fully-connected) neural networks, and convolutional neural networks. Again, to the best of our knowledge, this is the first time that these three statistical learning approaches are quantitatively compared on the same dataset. The diversity of the dataset increases the generality of the determined relationships, and its size is vital for robust training of convolutional neural networks. We make the 3D microstructures, their structural descriptors and effective properties, as well as the code used to study the relationships between them available open access

Surveying Europe’s only cave-dwelling chordate species (Proteus anguinus) using environmental DNA

In surveillance of subterranean fauna, especially in the case of rare or elusive aquatic species, traditional techniques used for epigean species are often not feasible. We developed a non-invasive survey method based on environmental DNA (eDNA) to detect the presence of the red-listed cave-dwelling amphibian, Proteus anguinus, in the caves of the Dinaric Karst. We tested the method in fifteen caves in Croatia, from which the species was previously recorded or expected to occur. We successfully confirmed the presence of P. anguinus from ten caves and detected the species for the first time in five others. Using a hierarchical occupancy model we compared the availability and detection probability of eDNA of two water sampling methods, filtration and precipitation. The statistical analysis showed that both availability and detection probability depended on the method and estimates for both probabilities were higher using filter samples than for precipitation samples. Combining reliable field and laboratory methods with robust statistical modeling will give the best estimates of species occurrence

Volunteer Conservation Action Data Reveals Large-Scale and Long-Term Negative Population Trends of a Widespread Amphibian, the Common Toad (Bufo bufo).

Rare and threatened species are the most frequent focus of conservation science and action. With the ongoing shift from single-species conservation towards the preservation of ecosystem services, there is a greater need to understand abundance trends of common species because declines in common species can disproportionately impact ecosystems function. We used volunteer-collected data in two European countries, the United Kingdom (UK) and Switzerland, since the 1970s to assess national and regional trends for one of Europe's most abundant amphibian species, the common toad (Bufo bufo). Millions of toads were moved by volunteers across roads during this period in an effort to protect them from road traffic. For Switzerland, we additionally estimated trends for the common frog (Rana temporaria), a similarly widespread and common amphibian species. We used state-space models to account for variability in detection and effort and included only populations with at least 5 years of data; 153 populations for the UK and 141 for Switzerland. Common toads declined continuously in each decade in both countries since the 1980s. Given the declines, this common species almost qualifies for International Union for the Conservation of Nature (IUCN) red-listing over this period despite volunteer conservation efforts. Reasons for the declines and wider impacts remain unknown. By contrast, common frog populations were stable or increasing in Switzerland, although there was evidence of declines after 2003. "Toads on Roads" schemes are vital citizen conservation action projects, and the data from such projects can be used for large scale trend estimations of widespread amphibians. We highlight the need for increased research into the status of common amphibian species in addition to conservation efforts focusing on rare and threatened species

Where Land and Water Meet: Making Amphibian Breeding Sites Attractive for Amphibians

The protection of wetlands is a cornerstone in the conservation of pond-breeding amphibians. Because protected wetlands are rarely natural areas, but are often man-made, at least in Europe, it is important that they are well managed to fulfill their intended function. Appropriate management requires knowledge of the ecology of the species, particularly habitat requirements. Here, we combine species monitoring data and habitat mapping data in an analysis where our goal was to describe the factors that determine the occupancy of amphibian species in federally protected amphibian breeding sites. As expected, every species had its own habitat requirements, often a combination of both a terrestrial and aquatic habitat (i.e., landscape complementation). In most species, occupancy was strongly positively affected with the amount of aquatic habitat, but predicted occupancy probabilities were low because the amount of aquatic habitat was low in most sites. The area or proportion of ruderal vegetation also had positive effects on multiple species, while other types of terrestrial habitat (e.g., meadows) led to low occupancy probabilities. The total area of the protected breeding sites was never included in a final model and connectivity was important only for one species (Triturus cristatus). The latter finding implies that the quality of the landscape between breeding sizes is more important than distance per se, while the former implies that the area of some specific habitats within breeding sites is crucial for high occupancies. Thus, increasing the amount of aquatic habitats and likewise terrestrial habitats within protected areas would make them more likely to achieve their conservation objectives. Our study is an example of how the joint analysis of monitoring data and habitat data (based on mapping in the field) can lead to evidence-based suggestions on how to improve conservation practice

Amphibians and plant-protection products: what research and action is needed?

Background: The majority of Swiss amphibians are threatened. There is a range of factors which have been discussed as possible causes for their decline, including plant protection products (PPPs). Results: The influence of PPPs on amphibian populations has not yet been studied to any great extent, neither for active ingredients nor for the wetting agents, breakdown products or tank mixtures. A further topic of discussion was how to better protect amphibians by reducing their exposure to PPPs in agricultural fields. Conclusion: Experts at a workshop concluded that further research is needed

Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians

Success stories are rare in conservation science, hindered also by the research-implementation gap, where scientific insights rarely inform practice and practical implementation is rarely evaluated scientifically. Amphibian population declines, driven by multiple stressors, are emblematic of the freshwater biodiversity crisis. Habitat creation is a straightforward conservation action that has been shown to locally benefit amphibians, as well as other taxa, but does it benefit entire amphibian communities at large spatial scales? Here, we evaluate a landscape-scale pond-construction program by fitting dynamic occupancy models to 20 y of monitoring data for 12 pond-breeding amphibian species in the Swiss state Aargau, a densely populated area of the Swiss lowlands with intensive land use. After decades of population declines, the number of occupied ponds increased statewide for 10 out of 12 species, while one species remained stable and one species further declined between 1999 and 2019. Despite regional differences, in 77% of all 43 regional metapopulations, the colonization and subsequent occupation of new ponds stabilized (14%) or increased (63%) metapopulation size. Likely mechanisms include increased habitat availability, restoration of habitat dynamics, and increased connectivity between ponds. Colonization probabilities reflected species-specific preferences for characteristics of ponds and their surroundings, which provides evidence-based information for future pond construction targeting specific species. The relatively simple but landscape-scale and persistent conservation action of constructing hundreds of new ponds halted declines and stabilized or increased the state-wide population size of all but one species, despite ongoing pressures from other stressors in a human-dominated landscape