The FrogID dataset: expert-validated occurrence records of Australia's frogs collected by citizen scientists

Current State of Conservation Physiology for Amphibians: Major Research Topics and Physiological Parameters

Analysis of physiological responses can be used to assess population health, identify threat factors, and understand mechanisms of stress. In addition to this, conservation physiologists have sought to establish potential management strategies for environmental change and evaluate the effectiveness of conservation efforts. From past to present, the field of conservation physiology is developing in an increasingly broader context. In this review, we aim to categorize the topics covered in conservation physiology research on amphibians and present the measured physiological parameters to provide directions for future research on conservation physiology. Physiological responses of amphibians to environmental stressors are the most studied topic, but conservation physiological studies on metamorphosis, habitat loss and fragmentation, climate change, and conservation methods are relatively lacking. A number of physiological indices have been extracted to study amphibian conservation physiology, and the indices have varying strengths of correlation with each subject. Future research directions are suggested to develop a comprehensive monitoring method for amphibians, identify interactions among various stressors, establish physiological mechanisms for environmental factors, and quantify the effects of conservation activities on amphibian physiology.

An invasive pathogen drives directional niche contractions in amphibians

Global change is causing an unprecedented restructuring of ecosystems, with the spread of invasive species being a key driver. While population declines of native species due to invasives are well documented, much less is known about whether new biotic interactions reshape niches of native species. Here we quantify geographic range and realized-niche contractions in Australian frog species following the introduction of amphibian chytrid fungus Batrachochytrium dendrobatidis, a pathogen responsible for catastrophic amphibian declines worldwide. We show that chytrid-impacted species experienced proportionately greater contractions in niche breadth than geographic distribution following chytrid emergence. Furthermore, niche contractions were directional, with contemporary distributions of chytrid-impacted species characterized by higher temperatures, lower diurnal temperature range, higher precipitation and lower elevations. Areas with these conditions may enable host persistence with chytrid through lower pathogenicity of the fungus and/or greater demographic resilience. Nevertheless, contraction to a narrower subset of environmental conditions could increase host vulnerability to other threatening processes and should be considered in assessments of extinction risk and during conservation planning. More broadly, our results emphasize that biotic interactions can strongly shape species realized niches and that large-scale niche contractions due to new species interactions-particularly emerging pathogens-could be widespread.

Anthropogenic habitat modification alters calling phenology of frogs

Anthropogenic habitat modification significantly challenges biodiversity. With its intensification, understanding species' capacity to adapt is critical for conservation planning. However, little is known about whether and how different species are responding, particularly among frogs. We used a continental-scale citizen science dataset of >226,000 audio recordings of 42 Australian frog species to investigate how calling-a proxy for breeding-phenology varied along an anthropogenic modification gradient. Calling started earlier and breeding seasons lengthened with increasing modification intensity. Breeding seasons averaged 22.9 ± 8.25 days (standard error) longer in the most modified compared to the least modified regions, suggesting that frog breeding activity was sensitive to habitat modification. We also examined whether calls varied along a modification gradient by analysing the temporal and spectral properties of advertisement calls from a subset of 441 audio recordings of three broadly distributed frog species. There was no appreciable effect of anthropogenic habitat modification on any of the measured call variables, although there was high variability. With continued habitat modification, species may shift towards earlier and longer breeding seasons, with largely unknown ecological consequences in terms of proximate and ultimate fitness.

Using citizen science to test for acoustic niche partitioning in frogs

The acoustic niche hypothesis proposes that to avoid interference with breeding signals, vocal species should evolve to partition acoustic space, minimising similarity with co-occurring signals. Tests of the acoustic niche hypothesis are typically conducted using a single assemblage, with mixed outcomes, but if the process is evolutionarily important, a pattern of reduced acoustic competition should emerge, on average, over many communities. Using a continental-scale dataset derived from audio recordings collected by citizen scientists, we show that frogs do partition acoustic space. Differences in calls were predominately caused by differences in spectral, rather than temporal, features. Specifically, the 90% frequency bandwidths of observed frog assemblages overlapped less than expected, and there was greater distance between dominant frequencies than expected. To our knowledge, this study is the first to use null models to test for acoustic niche partitioning over a large geographic scale.

Sounding the Call for a Global Library of Underwater Biological Sounds

Aquatic environments encompass the world’s most extensive habitats, rich with sounds produced by a diversity of animals. Passive acoustic monitoring (PAM) is an increasingly accessible remote sensing technology that uses hydrophones to listen to the underwater world and represents an unprecedented, non-invasive method to monitor underwater environments. This information can assist in the delineation of biologically important areas via detection of sound-producing species or characterization of ecosystem type and condition, inferred from the acoustic properties of the local soundscape. At a time when worldwide biodiversity is in significant decline and underwater soundscapes are being altered as a result of anthropogenic impacts, there is a need to document, quantify, and understand biotic sound sources–potentially before they disappear. A significant step toward these goals is the development of a web-based, open-access platform that provides: (1) a reference library of known and unknown biological sound sources (by integrating and expanding existing libraries around the world); (2) a data repository portal for annotated and unannotated audio recordings of single sources and of soundscapes; (3) a training platform for artificial intelligence algorithms for signal detection and classification; and (4) a citizen science-based application for public users. Although individually, these resources are often met on regional and taxa-specific scales, many are not sustained and, collectively, an enduring global database with an integrated platform has not been realized. We discuss the benefits such a program can provide, previous calls for global data-sharing and reference libraries, and the challenges that need to be overcome to bring together bio- and ecoacousticians, bioinformaticians, propagation experts, web engineers, and signal processing specialists (e.g., artificial intelligence) with the necessary support and funding to build a sustainable and scalable platform that could address the needs of all contributors and stakeholders into the future.

Estimating the movements of terrestrial animal populations using broad-scale occurrence data

As human and automated sensor networks collect increasingly massive volumes of animal observations, new opportunities have arisen to use these data to infer or track species movements. Sources of broad scale occurrence datasets include crowdsourced databases, such as eBird and iNaturalist, weather surveillance radars, and passive automated sensors including acoustic monitoring units and camera trap networks. Such data resources represent static observations, typically at the species level, at a given location. Nonetheless, by combining multiple observations across many locations and times it is possible to infer spatially continuous population-level movements. Population-level movement characterizes the aggregated movement of individuals comprising a population, such as range contractions, expansions, climate tracking, or migration, that can result from physical, behavioral, or demographic processes. A desire to model population movements from such forms of occurrence data has led to an evolving field that has created new analytical and statistical approaches that can account for spatial and temporal sampling bias in the observations. The insights generated from the growth of population-level movement research can complement the insights from focal tracking studies, and elucidate mechanisms driving changes in population distributions at potentially larger spatial and temporal scales. This review will summarize current broad-scale occurrence datasets, discuss the latest approaches for utilizing them in population-level movement analyses, and highlight studies where such analyses have provided ecological insights. We outline the conceptual approaches and common methodological steps to infer movements from spatially distributed occurrence data that currently exist for terrestrial animals, though similar approaches may be applicable to plants, freshwater, or marine organisms.

Species' traits drive amphibian tolerance to anthropogenic habitat modification

Anthropogenic habitat modification is accelerating, threatening the world's biodiversity. Understanding species' responses to anthropogenic modification is vital for halting species' declines. However, this information is lacking for globally threatened amphibians, informed primarily by small community-level studies. We integrated >126,000 verified citizen science observations of frogs, with a global continuous measure of anthropogenic habitat modification for a continental scale analysis of the effects of habitat modification on frogs. We derived a modification tolerance index-accounting for anthropogenic stressors such as human habitation, agriculture, transport and energy production-for 87 species (36% of all Australian frog species). We used this index to quantify and rank each species' tolerance of anthropogenic habitat modification, then compiled traits of all the frog species and assessed how well these equipped species to tolerate modified habitats. Most of Australia's frog species examined were adversely affected by habitat modification. Habitat specialists and species with large geographic range sizes were the least tolerant of habitat modification. Call dominant frequency, body size, clutch type and calling position (i.e. from vegetation) were also related to tolerance of habitat modification. There is an urgent need for improved consideration of anthropogenic impacts and improved conservation measures to ensure the long-term persistence of frog populations, particularly focused on specialists and species identified as intolerant of modified habitats.

Multi-species occupancy modeling provides novel insights into amphibian metacommunity structure and wetland restoration

A fundamental goal of community ecology is to understand species-habitat relationships and how they shape metacommunity structure. Recent advances in occupancy modeling enable habitat relationships to be assessed for both common and rare species within metacommunities using multi-species occupancy models (MSOM). These models account for imperfect species detection and offer considerable advantages over other analytical tools commonly used for community analyses under the elements of metacommunity structure (EMS) framework. Here, we demonstrate that MSOM can be used to infer habitat relationships and test metacommunity theory, using amphibians. Repeated frog surveys were undertaken at 55 wetland sites in southeastern Australia. We detected 11 frog species from three families (Limnodynastidae, Myobatrachidae, and Pelodryadidae). The rarest species was detected at only one site whereas the most common species was detected at 42 sites (naive occupancy rate 0.02-0.76). Two models were assessed representing two competing hypotheses; the best-supported model included the covariates distance to the nearest site (connectivity), wetland area, presence of the non-native eastern mosquitofish (Gambusia holbrooki), proportion cover of emergent vegetation, an interaction term between Gambusia and emergent vegetation cover, and the proportion canopy cover over a site. Hydroperiod played no detectable role in metacommunity structure. We found species-habitat relationships that fit with current metacommunity theory: occupancy increased with wetland area and connectivity. There was a strong negative relationship between occupancy and the presence of predatory Gambusia, and a positive interaction between Gambusia and emergent vegetation. The presence of canopy cover strongly increased occupancy for several tree frog species, highlighting the importance of terrestrial habitat for amphibian community structure. We demonstrated how responses by amphibians to environmental covariates at the species level can be linked to occupancy patterns at the metacommunity scale. Our results have clear management implications: wetland restoration projects for amphibians and likely other taxa should maximize wetland area and connectivity, establish partial canopy cover, and eradicate Gambusia or provide aquatic vegetation to mitigate the impact of this non-native fish. We strongly advocate the use of MSOM to elucidate the habitat drivers behind animal occupancy patterns and to derive unbiased occupancy estimates for monitoring programs.

Anuran accents: Continental-scale citizen science data reveal spatial and temporal patterns of call variability

Many animals rely on vocal communication for mating advertisement, territorial displays, and warning calls. Advertisement calls are species-specific, serve as a premating isolation mechanism, and reinforce species boundaries. Nevertheless, there is a great deal of interspecific variability of advertisement calls. Quantifying the variability of calls among individuals within a species and across species is critical to understand call evolution and species boundaries, and may build a foundation for further research in animal communication. However, collecting a large volume of advertisement call recordings across a large geographic area has traditionally posed a logistical barrier. We used data from the continental-scale citizen science project FrogID to investigate the spatial and temporal patterns of call characteristics in six Australian frog species. We found intraspecific call variability in both call duration and peak frequency across species. Using resampling methods, we show that variability in call duration and peak frequency was related to the number of individuals recorded, the geographic area encompassed by those individuals, and the intra-annual time difference between those recordings. We conclude that in order to accurately understand frog advertisement call variation, or "anuran accents," the number of individuals in a sample must be numerous (N ≥ 20), encompass a large geographic area relative to a species' range, and be collected throughout a species' calling season.

Citizen science implements the first intensive acoustics-based survey of insectivorous bat species across the Murray–Darling Basin of South Australia

Effective land management and biodiversity conservation policy relies on good records of native species occurrence and habitat association, but for many animal groups these data are inadequate. In the Murray–Darling Basin (MDB), the most environmentally and economically important catchment in Australia, knowledge gaps exist on the occurrence and habitat associations of insectivorous bat species. We relied on the interest and effort of citizen scientists to assist with the most intensive insectivorous bat survey ever undertaken in the MDB region of South Australia. We used an existing network of Natural Resource Management groups to connect interested citizens and build on historical observations of bat species using a fleet of 30 Anabat Swift bat detectors. The survey effort more than doubled the number of bat occurrence records for the area in two years (3000 records; cf. 2693 records between 1890 and 2018; freely available through the Atlas of Living Australia). We used multinomial logistic regression to look at the relationship between three types of environmental covariates: flight space, nearest open water source and vegetation type. There were no differences in species richness among the environmental covariates. The records have been, and will continue to be, used to inform government land management policy, more accurately predict the impact of development proposals on bat populations, and update conservation assessments for microbat species. A social survey tool also showed that participation in the project led to positive behaviours, and planned positive behaviours, for improving bat habitat on private land.