Bell Frog Research Articles

Identifying a limiting factor in the population dynamics of a threatened amphibian: The influence of extended female maturation on operational sex ratio

AbstractUnderstanding amphibian population dynamics is integral to mitigating severe declines that are occurring due to threats such as habitat removal and chytrid‐induced disease. Few studies have focused on sex‐specific population dynamics, despite the potential for these processes to alter colonisation and population turn‐over in newly created habitats. Here, we investigate sex‐specific population dynamics in the threatened green and golden bell frog (Litoria aurea) using intensive capture‐recapture methods in a newly created wetland complex and control sites. As hypothesised, females took longer to reach maturity compared to males. The length of female maturation was 3.9 times greater than that of males (428.68 days ± 107.6 SD and 110.16 days ± 20.59 SD, respectively). This resulted in a one‐year delay in female population size increase compared to the male population. The operational sex ratio (OSR) in the second year of monitoring in the created wetlands had the most disproportionate male bias out of any year and any site (12/1 male/female, male proportion = 0.92 ± 0.89–0.94 95% CI). In the third year, the OSR had become less male biased (2.6/1, male proportion = 0.72 ± 65–0.78 95% CI), likely attributed to the maturing of the females produced in the first year breeding events. We did not find any evidence that survival or detection probability influenced the observed OSRs in the created wetlands. Based on survival rates of each sex, we estimate that males are 77 times more likely to reach sexual maturity compared to females. We postulate that the combination of chytrid‐induced disease and sex‐biased maturation rates may be a driver of declines, especially in populations with limited recruitment. We encourage future research into investigating sex‐specific population dynamics of amphibians, especially relating to reintroduction ecology and disease.

Standing out in a crowd: Intraspecific variability in dorsal patterning allows for photo‐identification of a threatened anuran

AbstractIndividuals within amphibian populations are commonly identified using artificial marking techniques, such as toe clipping and microchipping. However, many species in this group may be strong candidates for visual identification from photographs given intraspecific variability in skin features. We investigated the potential for dorsal skin patterns to be used as natural markers for the photo‐identification of both juveniles and adults of the green and golden bell frog (Litoria aurea). This is a threatened species that has come under intense population monitoring using capture‐mark‐recapture procedures primarily involving the use of artificial markers, with no apparent investigation of the potential for natural markers to be used instead. We collected photographs of marked individuals to determine the level of intraspecific variability in dorsal patterning within a population. This photo‐database was subsequently used to create an online survey in which participants were asked to match separate images of query frogs from small image pools by comparing dorsal patterns. Photographs were taken on a smartphone device under field conditions to test whether this technique could be applied to the study of wild populations with little cost or expertise required. We showed that dorsal patterns are clear and distinct among L. aurea individuals and easily visualised from field‐acquired images to detect recapture events by eye with a low error rate. While an overwhelming majority of adults possessed dorsal patterning that can be easily distinguished by eye, juveniles often showed a complete absence of patterning, suggesting that photo‐identification may be more effective for adult stages. Nevertheless, we highlight the feasibility of collecting visual information on the natural markings of a threatened anuran, providing evidence that it may be used as a supplementary form of identification alongside more traditional techniques, highlighting a potential direction for the future monitoring of this species.

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The Bulletin of the Ecological Society of AmericaVolume 102, Issue 3 e01915 CoverFree Access Cover First published: 01 July 2021 https://doi.org/10.1002/bes2.1915AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract COVER PHOTO: An endangered green and golden bell frog (Litoria aurea), which was one of eleven frog species detected on Kooragang Island, Australia, during the recent study by Hamer et al. published in Ecological Applications (https://doi.org/10.1002/eap.2293). This species occupies a mosaic of wetland types on Kooragang Island. This individual was captured in an artificial waterbody in the industrial area of the island. Photo credit: Michael Mahony. Volume102, Issue3July 2021e01915 RelatedInformation

Rapid population increase of the threatened Australian amphibian Litoria aurea in response to wetlands constructed as a refuge from chytrid-induced disease and introduced fish

Amphibians have declined due to multiple impacts including invasive fish and the disease chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). Wetland restoration can be used to increase amphibian populations. However the design of created wetlands must account for threats such as Bd and introduced fish. There have been no attempts on a landscape level to manage these threats with habitat design. Here we monitored the green and golden bell frog (Litoria aurea) in 2.6 ha of constructed wetlands designed to enhance breeding and increase survival through passive mitigation of Bd and exotic fish. We compared the fecundity, adult population sizes, introduced fish occupancy, Bd prevalence and survival rates of frogs in created wetlands (CW) to three control sites to determine if and why the habitat design was successful. Monitoring involved weekly capture-recapture during the austral spring and summer for three L. aurea breeding seasons. We hypothesised that (1) if the CWs were successful in passively limiting fish colonisation, a larger number of breeding events would be detected compared to control sites which are known to be widely colonised by introduced fish. (2) If the wetlands were successful in passively mitigating Bd, then we would observe an equal or greater survival rate and equal to or lower Bd prevalence compared to control wetlands. We observed a 3.3-fold increase in adult population size in CW from season 1 to 2, and the population increased further in season 3.We found strong support for hypothesis (1) and weak support for (2). Based on these results, we conclude that this design was beneficial shortly after their formation primarily due to fish exclusion, but further study is required to determine if these benefits extend long-term. Future amphibian restoration studies are needed to improve the design of wetlands to enhance suppression of Bd.

Predator-free short-hydroperiod wetlands enhance metamorph output in a threatened amphibian: insights into frog breeding behaviour evolution and conservation management

Abstract Context Knowledge on the drivers of breeding behaviour is vital to understand amphibian ecology and conservation. Proposed drivers of amphibian reproductive behaviour include selection of optimum water quality, and avoidance of tadpole predators and competition. These hypotheses are underpinned by the logic that amphibians will choose breeding habitat that will result in enhanced metamorph output. Aims We aimed to infer key drivers that influence metamorph output in the threatened green and golden bell frog (Litoria aurea). We hypothesised that (1) metamorph output would be higher in recently refilled wetlands than in wetlands with a longer hydroperiod, (2) metamorph output would be negatively correlated with tadpole predator abundance, and (3) waterbodies with long hydroperiods would have higher abundances of aquatic predators and lower abundances of L. aurea tadpoles. Methods We tested these hypotheses by monitoring breeding, tadpole and predator abundances in a wild population of L. aurea. We coupled this with metamorph counts that were adjusted to represent per capita numbers via genetic means. We also ruled out the influence of detection probability in explaining the results with a manipulative experiment. Key results We found support for all three hypotheses and hence provide evidence that the adaptive behaviour of L. aurea to preference recently refilled wetlands is governed by the abundance of tadpole predators. We found metamorph counts per clutch to be 8.2-fold greater in short-hydroperiod wetlands (26 ± 15–44 95% CI) than in long-hydroperiod wetlands (3 ± 2–5 95% CI). Four predator taxa were associated with low metamorph output and two of these occurred in higher abundances in longer-hydroperiod wetlands. Conclusions and implications These results have provided evidence that the behavioural adaptation of L. aurea to select recently refilled wetlands has evolved in response to tadpole predation pressure. We recommend practitioners to conduct tadpole releases in newly refilled wetlands to enhance survival to metamorphosis in future reintroductions.

Seasonal variation in the prevalence of a fungal pathogen and unexpected clearance from infection in a susceptible frog species.

The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) causes the disease chytridiomycosis, which is a primary driver for amphibian population declines and extinctions worldwide. For highly susceptible species, such as the green and golden bell frog Litoria aurea, large numbers of Bd-related mortalities are thought to occur during the colder season (winter), when low temperatures favour the growth of the pathogen. However, extant L. aurea populations are persisting with Bd. We measured Bd prevalence and infection levels of wild L. aurea using capture-mark-recapture and radio-tracking methods. Using this information, we sought to determine host and environmental correlates of Bd prevalence and infection load. Mean ± SE infection load was higher in frogs sampled in autumn (431.5 ± 310.4 genomic equivalents; GE) and winter (1147.5 ± 735.8 GE), compared to spring (21.8 ± 19.3 GE) and summer (0.9 ± 0.8 GE). Furthermore, prevalence of Bd infection in L. aurea was highest in winter (43.6%; 95% CI 33.1-54.7%) and lowest in summer (11.2%; 95% CI 6.8-17.9%). Both prevalence and infection load decreased with increasing temperature. Seven frogs cleared their fungal infection during the coolest months when Bd prevalence was highest; however, these clearances were not permanent, as 5 frogs became infected again. Understanding the factors that allow amphibians to clear their Bd infections when temperatures are optimal for Bd growth presents the potential for manipulating such factors and provides an important step in future research.

Generation of reproductively mature offspring from the endangered green and golden bell frog Litoria aurea using cryopreserved spermatozoa.

Amphibians are becoming increasingly reliant on captive breeding programs for continued survival. Assisted reproductive technologies including gamete cryopreservation and IVF can help reduce costs of breeding programs, provide insurance against extinction and assist genetic rescue in wild populations. However, the use of these technologies to produce reproductively mature offspring has only been demonstrated in a few non-model species. We aimed to optimise sperm cryopreservation in the threatened frog Litoria aurea and generate mature offspring from frozen-thawed spermatozoa by IVF. We tested three concentrations (1.4, 2.1 and 2.8M) of the cryoprotectants dimethylsulfoxide (DMSO) and glycerol with 0.3M sucrose. Using DMSO was more likely to result in recovery of sperm motility, vitality and acrosome integrity than glycerol, regardless of concentration, with forward progressive motility being most sensitive to damage. The lowest concentrations of 1.4 and 2.1M provided the best protection regardless of cryoprotectant type. Spermatozoa cryopreserved in 2.1M DMSO outperformed spermatozoa cryopreserved in equivalent concentrations of glycerol in terms of their ability to fertilise ova, resulting in higher rates of embryos hatching and several individuals reaching sexual maturity. We have demonstrated that sperm cryopreservation and subsequent offspring generation via IVF is a feasible conservation tool for L. aurea and other threatened amphibians.

Preliminary evidence for a two‐for‐one deal: Wetland restoration for a threatened frog may benefit a threatened bat

SummaryHabitat restoration is an integral feature of wildlife conservation. However, funding and opportunities for habitat restoration are limited, and therefore, it is useful for targeted restoration to provide positive outcomes for non‐target species. Here, we investigate the possibility of habitat creation and management benefitting two threatened wetland specialists: the Green and Golden Bell Frog (Litoria aurea) and the Large‐footed Myotis (Myotis macropus). This study involved two components: (i) assessing co‐occurrence patterns of these species in a wetland complex created for the Green and Golden Bell Frog (n = 9) using counts, and (ii) comparing foraging activity of Large‐footed Myotis in wetlands with low and high aquatic vegetation (n = 6 and 7, respectively) using echolocation metres. Since Large‐footed Myotis possesses a unique foraging behaviour of trawling for aquatic prey, we hypothesised that foraging activity of this species would be higher in wetlands with low aquatic vegetation coverage. Additionally, we provide observations of its potential prey items. We identified one created wetland where both species were found in relatively high numbers, and this wetland had a permanent hydrology, was free of the introduced fish Gambusia (Gambusia holbrooki) and had low aquatic vegetation coverage. We also found that Myotis feeding activity was significantly higher in low aquatic vegetation coverage wetlands (x̅ = 65.72 ± 27.56 SE) compared to high (x̅ = 0.33 ± 0.33 SE, P = 0.0000). Although this is a preliminary study, it seems likely that Green and Golden Bell Frog and Large‐footed Myotis would gain mutual benefit from wetlands that are constructed to be permanent, that are Gambusia free, low in aquatic vegetation coverage, and are located in close to suitable roosting habitat for Large‐footed Myotis. We encourage adaptive aquatic vegetation removal for Green and Golden Bell frog as this may have benefits for Large‐footed Myotis. The evidence suggests that the former may be a suitable umbrella species for the latter.

Wetland Restoration for the Threatened Green and Golden Bell Frog (Litoria aurea): Development of a Breeding Habitat Designed to Passively Manage Chytrid-Induced Amphibian Disease and Exotic Fish

Amphibians are under threat from many drivers resulting in declining populations. Restoration and creation of habitat is a method used to reverse amphibian declines. The green and golden bell frog (Litoria aurea) is distributed in southeastern Australia, and is threatened by the fungal pathogen Batrachochytrium dendobatidis (chytrid), an introduced fish (the plague minnow, Gambusia holbrooki), and habitat loss. There have been numerous wetland restoration attempts to combat population declines in this species, which have been largely unsuccessful in producing persisting populations. Here we present a robust model for the creation of breeding habitat for the L. aurea population on Kooragang Island, New South Wales, which is based off thorough review of the literature and past pilot studies and experiments. We describe in detail the habitat, land use history, and wetland habitat design formulation and construction so that the context of the habitat creation is understood and so construction can be repeatable and the design can be further refined. The habitat features passive controls for chytrid and G. holbrooki, and contains the most optimum breeding habitat for L. aurea based upon current knowledge. This is the first attempt in our knowledge to create wetlands in an open system that have the potential to passively manage chytrid.

Observations of an unexpected abundance of estuarine mosquitoes associated with an urban freshwater wetland

ABSTRACT Urban freshwater wetlands have been identified as a potential source of mosquitoes of pest and public health concern in Australia. Mosquitoes most commonly associated with these habitats include Anopheles annulipes, Culex annulirostris, Culex quinquefasciatus, Coquillettidia linealis and Mansonia uniformis. However, adaptive management of freshwater wetlands for wildlife conservation or vegetation management can alter the local environmental conditions and may provide opportunities for other mosquito species to exploit these habitats. A series of small wetlands at Sydney Olympic Park, NSW, were drained in spring 2016 and allowed to refill via rainfall to improve conditions for the endangered green and golden bell frog Litoria aurea. Below-average rainfall was experienced that summer and the wetlands did not fully refill until early autumn. Surprisingly, immature stages of the estuarine mosquito, Aedes vigilax, were observed in the freshwater wetlands in exceptional abundances during this period. Adjacent to these freshwater wetlands there are extensive saltmarsh and mangrove habitats where highly abundant populations of Ae. vigilax are common. Observations of use of freshwater habitats by this estuarine mosquito have implications for urban freshwater wetland management and rehabilitation strategies, which currently do not consider the potential pest and public health issues associated with estuarine mosquitoes.

A simple design feature to increase hydro‐period in constructed ephemeral wetlands to avoid tadpole desiccation‐induced mortality

SummaryHere, we identify an easily implemented wetland design feature that can prolong tadpole survival of the threatened Green and Golden Bell Frog (Litoria aurea). We observed small depressions that naturally formed within some wetlands following the construction of habitat for this species. We observed that wetlands containing depressions prolonged the survival of Green and Golden Bell Frog tadpoles during periods of rapid wetland drying whereas wetlands that did not contain depressions in the same circumstances dried, causing 100% mortality in tadpoles present. We recommend that this concept be considered as a design feature in future wetland construction for Green and Golden Bell Frog and other ephemeral wetland breeding amphibians and we provide commentary on how the benefits of this feature can be maximised. This simple design feature may be important for amphibian restoration, particularly considering climate change.

Chemosociality in Multispecies Worlds

AbstractChemosocial communities have formed in Sydney, Australia, as a result of encounters with industrial pollution. If biosociality involves social relationships that emerge from biological conditions, then chemosociality involves altered, attenuated, or augmented relationships that emerge with chemical exposures. Some social groups have coalesced around place-based political action, while other chemosocial associations have proved to be ephemeral, evanescent, and conditional. Building on earlier work by multispecies ethnographers who have studied social relationships among humans and animals, this article follows chemicals into more-than-human realms. Fragile multispecies worlds have emerged in a complex landscape shaped by chemical weapons industries, municipal landfills, government remediation programs, real estate speculation, and a multitude of chemical and biological agents. Legacy dumping grounds in the Sydney Olympic Park have become habitat for the green and golden bell frog, an endangered species. While the normal world order of this frog has been lost with the spread of a deadly fungal disease, toxic chemicals have enabled the continuation of its social life. Temporary spaces of immunity have emerged where life is protected and threats are negated by poisonous compounds that double as a cure.

Management of urban wetlands for conservation can reduce aquatic biodiversity and increase mosquito risk

Abstract Global wetland loss means constructed urban wetlands are an increasingly valuable resource for conservation. However, priorities for managing urban wetlands for conservation are often seen to conflict with management to reduce potential mosquito risks, such as nuisance biting and pathogen transmission. Understanding the ecological consequences of wetland management practices is vital to maximize the conservation value of urban wetlands without negatively impacting public health; however, management practices are often untested. We conducted a landscape‐scale experiment to test the ecological impacts of an existing urban wetland management regime, in which a group of urban wetlands are drained annually to reduce the abundance of an invasive fish, the plague minnow Gambusia holbrooki, and then refilled to provide breeding habitat for a threatened frog, the green and golden bell frog Litoria aurea. We collected and compared aquatic macroinvertebrates and mosquito larvae from these refilled wetlands, and adjacent undrained wetlands, as well as sampling adult mosquito populations on four occasions across summer and autumn. Wetland draining had a significant effect on aquatic macroinvertebrates and larval mosquitoes. Twice as many macroinvertebrates were collected from drained wetlands compared to undrained wetlands, and almost all mosquito larvae were collected from drained wetlands. Differences in macroinvertebrate assemblages and larval mosquitoes at drained and undrained wetlands decreased over time, but total macroinvertebrate abundance and taxa richness did not. Synthesis and applications. While conserving threatened habitats and species is vitally important, our results highlight how wetland management practices can unintentionally impact non‐target species, and potentially public health. As constructed urban wetlands become more common, so too does the need for routine maintenance and management of threatened and invasive species. It is essential that future design and management of urban wetlands considers the impact mosquitoes might have on humans. Pre‐emptive action to control geographically relevant vectors of mosquito‐borne pathogens and nuisance biting species would reduce human exposure to mosquitoes and associated negative impacts, and increase positive conservation outcomes associated with urban wetlands.

Population stability in an unmanaged population of the green and golden bell frog in northern New South Wales, Australia

Population monitoring is required to guide conservation programs. We conducted a capture–mark–recapture study of a population of the vulnerable green and golden bell frog (Litoria aurea) at the northern end of its range. Frogs were captured and marked over three breeding seasons (2015/16, 2016/17, 2017/18) in a large coastal lagoon. We aimed to: (1) produce annual estimates of population size to describe population trajectory, and (2) investigate monthly variation in abundance, capture probability, and temporary emigration to understand how these factors change at a finer temporal scale. Frog abundance varied across the three annual breeding seasons: 60–280 adult males, 120–190 adult females, and 90–420 subadults. We infer that the population is stable because adult abundance estimates were higher after 2015/16. Because our study sampled only half the available breeding habitat, the overall population may number 350–850 adults. Our modelling revealed >40 males but <20 females were detected in the sample area in our monthly samples. Estimates of temporary emigration were high (males: 0.54; females: 0.79), suggesting behaviour that made frogs unavailable for capture between months. Our results suggest that monitoring at greater than annual intervals should be adequate to monitor the future trend of this population.

A frog-derived bionic peptide with discriminative inhibition of tumors based on integrin αvβ3 identification.

Aureins, natural active peptides extracted from skin secretions of Australian bell frogs, have become a research focus due to the antitumor effects caused by lysing cell membranes. However, clinical translation of Aureins is still limited by non-selective toxicity between normal and cancer cells. Herein, by structure-activity relationship analysis and rational linker design, a dual-function fusion peptide RA3 is designed by tactically fusing Aurein peptide A1 with strong anticancer activity, with a tri-peptide with integrin αvβ3-binding ability which was screened in our previous work. Rational design and selection of fusion linkers ensures α-helical conformation and active functions of this novel fusion peptide, inducing effective membrane rupture and selective apoptosis of cancer cells. The integrin binding and tumor recognition ability of the fusion peptide is further validated by fluorescence imaging in cell and mouse models, in comparison with the non-selective A1 peptide. Meanwhile, increased stability and superior therapeutic efficacy are achieved in vivo for the RA3 fusion peptide. Our study highlights that aided by computational simulation technologies, the biomimetic fusion RA3 peptide has been successfully designed, surmounting the poor tumor-selectivity of the natural defensive peptide, serving as a promising therapeutic agent for cancer treatment.

Alignment-based design and synthesis of new antimicrobial Aurein-derived peptides with improved activity against Gram-negative bacteria and evaluation of their toxicity on human cells.

Considering the worldwide increasing prevalence of resistance to traditional antibiotics, it is necessary to find new antibiotics to deal with this issue. Recently, antimicrobial peptides (AMPs) have been proposed as new antimicrobial agents. Aureins are a family of AMPs that are isolated from Green and Golden Bell Frogs. These peptides have a favorable antibacterial activity against Gram-positive bacteria. We designed two peptides derived from natural Aurein enjoying alignment-based design method. After synthesis of the peptides, their secondary structure was checked by circular dichroism. Consequently, the antibacterial effects of these peptides were investigated by determining the minimum inhibitory concentration (MIC) and bactericidal concentration. Eventually, the toxicity of these peptides was determined by MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) assay on normal human skin cells (Hu02 cell line). Natural Aurein1.2 was used as a natural control to compare the properties in all stages. The results indicated that these new peptides had medium-upward antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis (MIC of 8-64 μg/mL) and weak bactericidal activity against Staphylococcus aureus (MIC of 128-256 μg/mL). Also, MTT assays results showed that AureinN2 is less toxic than AureinN1 and Aurein1.2. Toxicity of AureinN2 for Hu02 cell lines was between 20 and 40% at the concentration of 8-500 μg/mL. In this study, we were able to improve antimicrobial activity of two synthetic derivatives of the Aurein family against Gram-negative bacteria by using machine-learning algorithm and other in silico methods.

Alanine Scanning Studies of the Antimicrobial Peptide Aurein 1.2

Antimicrobial peptides (AMPs) are compounds widely distributed in nature that display activity against a broad spectrum of pathogens. Amphibian skin, as an organ rich in pharmacologically active peptides, appears to be an interesting source of novel AMPs. Aurein 1.2 (GLFDIIKKIAESF-NH2) is a short 13-residue antimicrobial peptide primarily isolated from the skin secretions of Australian bell frogs. In this study, the alanine scan of aurein 1.2 was performed to investigate the effect of each amino acid residue on its biological and physico-chemical properties. The biological studies included determination of minimum inhibitory concentration, activity against biofilm, and inhibitory effect on its formation. Moreover, the hemolytic activity as well as serum stability was determined. The hydrophobicity of peptides and their self-assembly were investigated using reversed-phase chromatography. In addition, their helicity was calculated from circular dichroism spectra. The results not only provided information on structure-activity relationship of aurein 1.2 but also gave insights into design of novel analogs of AMPs in the future.

Accessible habitat and wetland structure drive occupancy dynamics of a threatened amphibian across a peri-urban landscape

Populations of aquatic-breeding amphibians are declining from habitat loss, fragmentation and degradation. Identifying how populations are affected by landscape barriers such as roads is essential for conservation and requires understanding the processes underpinning species occupancy in fragmented landscapes. Here, I assessed relationships between the occupancy dynamics of the threatened green and golden bell frog (Litoria aurea) and accessible habitat; i.e., the area of breeding and non-breeding habitat around a wetland that can be reached by an amphibian without having to cross a highway. I hypothesised that relationships between occupancy and accessible habitat would be stronger than relationships with the area of extant native vegetation, road density or distance to the highway. I also examined relationships with local habitat variables over a three-year period. Relationships with accessible habitat were stronger and more certain in explaining L. aurea occupancy and colonisation than other landscape variables. Accessible habitat was positively associated with wetland occupancy, which suggests the highway is having a barrier effect on the population. There was a positive relationship between road density and the probability of local extinction. Occupancy rates at highway compensatory ponds increased from near-zero within six months of pond construction, to >30% after 12 months. There was a negative relationship between local extinction and aquatic vegetation cover, highlighting the importance of habitat structure for L. aurea. Urban planners should consider accessible habitat when managing amphibian species in rapidly urbanising landscapes, so that all habitats required throughout a species’ life cycle are protected.

Floodplain ecosystem dynamics under extreme dry and wet phases in semi‐arid Australia

Abstract Ecological networks are a cornerstone of ecological theory, offering an integrated approach to understanding food webs and ecosystem dynamics required for restoration and conservation ecology. We investigated ecological network dynamics in a large floodplain undergoing extreme variation in water availability, with drought and subsequent flooding representing a resource pulse. We used structural equation models to quantify ecological network dynamics for the Lowbidgee floodplain (Australia), based on surveys over 5 years while the floodplain transitioned from extremely dry (2009, 2010) to wet (2011) and post‐wet (2013, 2014) conditions. We identified significant associations of species and trophic guilds with inundation at the site and floodplain scale, which allowed us to quantify the strength of biotic interactions within the network and the stability of interactions under differing patterns of resource availability. At the floodplain scale, most taxa responded strongly in distribution and abundance to the 2011 resource pulse, a widespread flood, but this response did not persist during subsequent years of moderate floods. In contrast, fish species, both native and exotic, responded strongly only in the post‐wet period. At the fine spatial scale (i.e., sites), complex responses were observed, with only waterbirds, frogs and tadpoles positively associated with inundation, while fish species showed a range of associations with fine‐scale inundation. Biotic interactions within sites, across all trophic guilds, were predominately overridden by inundation and water temperature, mediated by strong associations with aquatic vegetation. Stratifying the ecological network to dry, wet and post‐wet periods highlighted varying associations of taxa with fine‐scale inundation, generally responding synchronously to resource pulses, with relatively weak biotic interactions. Associations with site‐scale inundation were strongest during the post‐wet period for fishes and frogs. Only Litoria spp. (Hylidae) tadpoles, waterbirds and aquatic vegetation had positive associations with site‐scale inundation during the dry period. We conclude that responses of trophic guilds are largely dependent on the way they interact with their environment at particular spatial and temporal scales. Our investigation of this ecological network reinforced the importance of hydrological drivers over biotic interactions, with clear implications for the management of environmental flows, particularly in systems recovering from long‐term flow alteration. Management efforts should focus environmental flows to promote specialist species (e.g., southern bell frog, Litoria raniformis) and Murray hardyhead (Craterocephalus fluviatilis: Atherinidae), waterbirds and aquatic vegetation over the more generalist fish species that have established because of the loss of the natural flow regime.

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

AbstractInvasive 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.