Six‐year demographic study reveals threat of stochastic extinction for remnant populations of a threatened amphibian

Sustained demographic studies are essential for early detection of species decline in time for effective management response. A paucity of such background data hindered the potential for successful conservation during the global amphibian decline and remains problematic today. The current study analysed 6 years of mark‐recapture data to determine the vital demographic rates in three habitat precincts of the threatened frog, Litoria aurea (Hylidae) and to understand the underlying causes of variability in population size. Variability in population size of L. aurea was similar to many pond‐breeding species; however this level of fluctuation is rare among threatened amphibians. Highly variable populations are at greater risk of local extinction and the low level of connectivity between L. aurea populations means they are at a greater risk of further decline due to stochastic extinction events and incapacity to recolonize distant habitat. We recommend that management of this species should encourage recolonization through creation of habitat corridors and reintroduction of L. aurea to areas where stochastic extinction events are suspected.     

Calling phenology and detectability of a threatened amphibian (Litoria olongburensis) in ephemeral wetlands varies along a latitudinal cline: Implications for management

Amphibian reproductive biology and activity are highly sensitive to environmental cues. For amphibian conservation in the face of climate change, a clear priority is to investigate impacts of variable weather on breeding activity and detectability. This study assessed variation in the phenology, intensity and detectability of calling for a threatened temporary wetland breeding species, Litoria olongburensis. Acoustic and visual surveys were conducted monthly from August 2009 to July 2011 over the species latitudinal range in eastern Australia. Calling phenology of L. olongburensis varied spatially and temporally within and among latitudinal clusters. Detectability of frogs also varied among months and transects, and also with the type of survey conducted (visual vs. acoustic). Air temperature was a strong predictor for the onset of the calling season (early spring); however, peaks in calling abundances were primarily driven by monthly accumulated rainfall. The duration of the calling season varied among latitudinal clusters, becoming narrower moving south, reflecting clinal variation in weather patterns. This study presents a framework for amphibian species management using a combination of survey techniques and the climatic conditions influencing detectability. Applied along the latitudinal gradient, it provides data for predicting the likely impacts of climate change on amphibian activity and reproduction.     

Tadpole fingerprinting: Using tail venation patterns to photo-identify tadpole individuals of a threatened frog

Traditional methods for identifying individual amphibians in capture–mark–recapture (CMR) studies have been primarily confined to post-metamorphic stages, using artificial markers that come with a variety of limitations. An alternative that may open CMR studies to earlier life stages involves the use of a species' natural external markers in photo-based identification. In this study, we investigated whether it was possible to distinguish tadpoles of the threatened green and golden bell frog (Litoria aurea) at the individual level based on tail venation patterns. We collected photographs of the tails of captive-raised tadpoles using a smartphone over a 4-week period. This photo-library was used to create an electronic survey where participants were asked to detect matches for query tadpoles from small image pools. We found that most participants agreed on a match for each query, with perfect consensus achieved for most queries (83%). We detected a 14% decline in perfect consensus when participants were asked to match images of tadpoles separated by longer time intervals, suggesting that it is more difficult to visually identify recapture events of L. aurea tadpoles over extended periods due to changes to tail appearance. However, consensus was obtained by participants for all queries, with all matches verified as being correct by the primary researcher. The strength of agreement among participants with no prior experience in matching tadpole tails suggests that there is sufficient inter-individual variation in this feature for individuals to be manually identified. We thus propose that photo-identification is likely to be a valid, non-invasive technique that can be used for short-term studies on tadpole populations that display tail venation. This offers an alternative to artificial markers that may not allow for individual identification, while also opening up tadpole monitoring programmes to citizen scientists who can be recruited online to process image data from home.     

Community level impacts of invasive mosquitofish may exacerbate the impact to a threatened amphibian

Invasive fish threaten many native freshwater fauna. However, it can be difficult to determine how invasive fish impact animals with complex life cycles as interaction may be driven by either predation of aquatic larvae or avoidance of fish‐occupied waterbodies by the terrestrial adult stage. Mosquitofish (Gambusia spp.) are highly successful and aggressive invaders that negatively impact numerous aquatic fauna. One species potentially threatened by Gambusia holbrooki is the green and golden bell frog (Litoria aurea). However, G. holbrooki's role in this frog's decline was unclear due to declines driven by the chytrid fungal disease and the continued co‐existence of these fish and frogs in multiple locations. To clarify the extent to which Gambusia is impacting L. aurea, we conducted 3 years of field surveys across a deltaic wetland system in south‐east Australia. We measured the presence and abundance of aquatic taxa including G. holbrooki, and L. aurea frogs and tadpoles, along with habitat parameters at the landscape and microhabitat scale. Generalized linear models were used to explore patterns in the abundance and distributions of L. aurea and G. holbrooki. We found strong negative associations between G. holbrooki and tadpoles of most species, including L. aurea, but no apparent avoidance of G. holbrooki by adult frogs. Native invertebrate predators (Odonata and Coleoptera) were also absent from G. holbrooki‐occupied ponds. Due to the apparent naivety of adult frogs toward G. holbrooki, the separation of G. holbrooki and tadpoles, plus the abundance of alternative predators in G. holbrooki‐free ponds, we conclude that the impact of G. holbrooki on L. aurea recruitment is likely substantial and warrants management action.     

Habitat characteristics predict occupancy patterns of the endangered amphibian Litoria raniformis in flow‐regulated flood plain wetlands

Identification of habitat features that are strongly associated with the occurrence of threatened species is important in terms of predicting impacts of habitat change and identifying key habitats for conservation. In this paper, we apply habitat‐based statistical models to predict occupancy patterns of the endangered southern bell frog (Litoria raniformis) across inland New South Wales (Australia). Litoria raniformis previously occupied a wide range of natural and man‐made waterbodies across a large geographic range, including flood plain wetlands, oxbow lagoons, irrigation canals and rice bays. Alteration of natural flooding regimes has affected a large proportion of habitats within the historical range of Litoria raniformis, but it is not clear how these changes have influenced habitat occupancy patterns. Fifty‐two waterbodies were surveyed for presence/absence of Litoria raniformis in 2001 and 2004. Stepwise logistic regression models were generated to select a subset of variables that best predicted occupancy. Using three predictor variables, vacant and occupied habitats could be predicted with an accuracy of 90% and 70%, respectively. The predictor variables were: the interaction between wetland hydrology and complexity of aquatic vegetation, complexity of fringing vegetation and water temperature. While this study demonstrated that a range of waterbody types were occupied by Litoria raniformis, these habitats shared common hydrological conditions and vegetation characteristics. Altered flooding regimes and reductions in the complexity of aquatic and fringing vegetation are likely to increase the probability of localized extinctions of Litoria raniformis populations.     

Factors influencing persistence of a threatened amphibian in restored wetlands despite severe population decline during climate change driven weather extremes

Biodiversity and Conservation - Biodiversity is in global decline during the Anthropocene. Declines have been caused by multiple factors, such as habitat removal, invasive species, and disease,...     

开封市城市水系微生境特征对两栖动物多样性的影响

两栖类生物生活史独特对环境变化极其敏感,是环境变化的重要指示物种.开封城市水系的建设直接影响两栖类生物栖息地与两栖类生物多样性.本研究通过设置样线,采用目视遇测法对开封市水系中的两栖类生物进行调查,并采集相应的生境因子变量.采用Shannon多样性指数、Pielou均匀度指数、Simpson优势度指数研究了不同生境类型...     

Evaluating monitoring methods to guide adaptive management of a threatened amphibian (Litoria aurea)

Prompt detection of declines in abundance or distribution of populations is critical when managing threatened species that have high population turnover. Population monitoring programs provide the tools necessary to identify and detect decreases in abundance that will threaten the persistence of key populations and should occur in an adaptive management framework which designs monitoring to maximize detection and minimize effort. We monitored a population of Litoria aurea at Sydney Olympic Park over 5 years using mark–recapture, capture encounter, noncapture encounter, auditory, tadpole trapping, and dip‐net surveys. The methods differed in the cost, time, and ability to detect changes in the population. Only capture encounter surveys were able to simultaneously detect a decline in the occupancy, relative abundance, and recruitment of frogs during the surveys. The relative abundance of L. aurea during encounter surveys correlated with the population size obtained from mark–recapture surveys, and the methods were therefore useful for detecting a change in the population. Tadpole trapping and auditory surveys did not predict overall abundance and were therefore not useful in detecting declines. Monitoring regimes should determine optimal survey times to identify periods where populations have the highest detectability. Once this has been achieved, capture encounter surveys provide a cost‐effective method of effectively monitoring trends in occupancy, changes in relative abundance, and detecting recruitment in populations.     

Experimental slab salvage and reinstatement after pipeline construction in a threatened grassland community

The protection and management of grasslands is a priority to conserve biodiversity, particularly in fragmented landscapes subject to human‐induced disturbance. We examined the success of salvage and reinstatement of multiple 90 m² slabs of modified temperate grassland in a pipeline construction corridor in south‐eastern Australia and compared it with a reinstated topsoil treatment (i.e. standard pipeline reinstatement practice) and an undisturbed control. Thirty‐six plots (each 9 × 10 m) representing the three treatments were monitored across six locations, pre‐ and postconstruction every 3 months for 2 years. We sampled 18 vegetation/habitat variables to examine the effect of treatments over time. Introduced grass cover was consistently higher than native grasses for both treatments, and the cover of introduced grasses increased over time in both treatments. Conversely, control plots had considerably higher native grass cover than the slab and reinstated topsoil treatments. Native species richness was not negatively affected by the slab reinstatement process. Our results suggest that in this instance, slab replacement was an ineffective way to reinstate native grasslands, as it appeared to confer minimal benefit when compared to the standard practice of reinstating topsoil. This was most likely due to the high degree of disturbance to slabs during the reinstatement process.     

人工湿地及其在我国小城市污水处理中的应用

小城市污水处理是我国面临的急待解决的环境问题,通过分析我国小城市污水的水质特点和处理技术要求,得出人工湿地处理技术具有投资低、出水水质好、耗能低、抗冲击力强、操作简单和运行费用低等优点,在解决我国小城市污水处理方面具有广阔的应用前景,应加强该方面的研究。     

The performance of a multi-stage system of constructed wetlands for urban wastewater treatment in a semiarid region of SE Spain

This paper describes the results obtained in an experimental multi-stage system of created wetlands in Mojacar, in semiarid SE Spain, operating from June to October 1997. We compare the removal efficiency of four different series of treatments each consisting of three stages, using different flow rates of sewage, flow regimes, types of substrate and influents. Pretreated water from an anaerobic stabilization pond and treated water from the last pond of a lagoon system were used, the latter to test the system's suitability as a complementary system for removing nitrogen and phosphorus. In spite of the initial high wastewater concentrations, the effluent conforms to the strictest European norms (directive 91/271) for primary and secondary retention. A net treatment area of 2.3 m²/PE showed a high performance for SS (90–96%), COD (87%) and BOD₅ removal (90%) during the early stages of operation; however, nutrient removal was lower than was expected as compared with other studies. The addition of iron to the substrate improved phosphorus retention significantly (from 55 to 66%). The decrease of the net treatment area to 1.2 m²/PE did not significantly affect the wetland performance, with the exception of COD removal (78%). Series fed with treated water from the lagoon system (1.6 m²/PE) noticeably improved the quality of the effluent (average values of 7 mg/l total-N and 3 mg/l total-P).     

不同形状城市湿地对周边环境温湿度的影响

2015年春、夏、秋季选择大庆市区5种不同形状特征的城市湿地及周边环境作为研究对象,利用小尺度定量测定的方法,分析城市湿地形状特征对周边环境温、湿效益的影响.结果表明: 不同形状特征的城市湿地均具有增湿降温效应.其中,夏季的增湿降温效应最强,春季其次,秋节最差.形状特征对湿地的降温增湿能力具有显著影响,不规则形状湿地>规则形状湿地(近圆形湿地、近矩形湿地)>长条形状湿地;增湿降温日变化受环境温度影响较大,即早晚弱、中午强,春、秋季增湿降温幅度最大的时段为12:00—14:00,夏季增湿降温幅度最大的时段为14:00—16:00.     

Cross‐scale effects of structural and functional connectivity in pond networks on amphibian distribution in agricultural landscapes

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Population density,microhabitat use,and size characteristics of Pseudothelphusa dugesi,a threatened species of freshwater crab from Mexico (Brachyura: Pseudothelphusidae)

The brachyuran crab Pseudothelphusa dugesi, or cangrejito barranqueño, is an endangered species endemic to Cuernavaca, Morelos, in central Mexico. Individuals of P. dugesi inhabit freshwater springs, which are affected by human actions through wastewater drainage, eutrophication, exploitation, and invasive predators such as rainbow trout (Oncorhynchus mykiss). In this study, we evaluated the population density, microhabitat use, and size characteristics of P. dugesi. Sampling was conducted in May, July, and December of 2018 and March of 2019, during the dry and rainy seasons in a natural protected area, the Barranca de Chapultepec. Population density was 0.082 crabs/m², female density was 0.052 crabs/m², and male density was 0.112 crabs/m²; ovigerous females were not observed. Males were more abundant than females; the female: male ratio was 1:2.14. Males and females had similar carapace widths and lengths, left and right chelae lengths, and mass. Individuals of P. dugesi were found mostly under or between rocks and under leaf litter. Individuals were more active at night. An understanding of the biology and population characteristics of P. dugesi will help conservationists to develop protective measures and a conservation strategy for this endangered Mexican freshwater crab species.     

红树林湿地在海岸生态系统维护中的功能*

综述了红树林湿地在海岸生态系统中所具有的维护生物多样性、防风消浪、促淤护岸、防灾减灾、净化海水、调节大气和美化海岸带景观等方面的功能。探讨了广东及华南沿海红树林的分布状况和存在问题,指出了华南沿海现存的红树林湿地正在遭受严重的威胁和破坏。华南沿海现存红树林湿地面积仅有1.5×10⁵hm²,比历史最大面积减少了70%;广东省的红树林湿地由10年前的1.47×10⁴hm²减少到现在的9100hm²,减少了38%。提出了建立和完善红树林自然保护网络系统、积极实施红树林湿地生态修复工程、注重红树林的引种和种苗培育技术研究、充分评估红树林湿地的巨大生态效价等对策与建议。     

Highlighting the effects of land-use change on a threatened amphibian in a human-dominated landscape

In Western Europe, habitat loss and landscape fragmentation has led to significant population decline in various animal groups, including amphibians. The extinction of the last natural populations of the yellow-bellied toad in Belgium, Luxembourg and several regions of southern and western France suggests a widespread decline. By using site-occupancy models and adding covariates corresponding to the human-influenced features of the landscape, we tried to identify the relative effects of different land-use types on the species’ distribution pattern in a man-made environment (the Alsatian Rhine floodplain in France). We recorded presence–absence data in 150 forest sample plots (300 × 300 m) and then modeled species distribution while taking into account detection errors in the field. Land-use was recorded on two spatial scales: within the forest sample plots and in a 1500 m radius buffer area around the forest plots. In the forest plots, toad occurrence was negatively correlated with loss of forest cover to agricultural land. In contrast, occurrence is positively correlated with the density of human-made rutted dirt paths and tracks, which provide semi-natural breeding sites. In the 1500 m radius buffer zones around forest plots, toad occurrence was negatively correlated with the density of urbanization and road networks. These results can be used to plan conservation strategies for amphibians in human-dominated landscapes.