There’s dew on the grass now, above the swamp. It was a given after a such a clear day. No clouds, sun goes down, temperature plummets. That’s the way it goes in Upper Plenty in spring. But the two men knee deep in the swamp have come prepared. Woolen beanies, heavy pants and stout jackets were the first items that went into the car. Below the thermocline, where the frigid night air flows over the warm water, mists are drifting like currents among the Water Ribbon and Mud Dock. And therein the frogs are calling. The chorus rises and falls with a mysterious synchrony, as hundreds of Southern Bell Frogs float and call and squabble. Bill Sherwin – a newly minted PhD student at the University of Melbourne – is on a steep learning curve, watching his supervisor Murray Littlejohn bag frog after frog. Yet the frogs call on, near oblivious to these strange new predators and the regular alarm calls punctuating the still night air. It’s October 1976.

Four-hundred kilometers north, on the Southern Tablelands of NSW, an equivalent scene plays out. Bob Humphries is embarking on the final field season of his ambitious PhD project. In a small, spring-fed farm dam, Bob wades through dense beds of Pondweed capturing as many of the resident Southern Bell Frogs and Green and Golden Bell Frogs as his frigid limbs will allow. In spite of his rapidly fading dexterity, he needs to check for toe-clips on each and every one of these stunning green frogs to decode their population dynamics. Are they animals he’s caught and marked before? Or are they new to the population, either being recruited late in the previous summer or having immigrated from another nearby pond?

That spring in 1976 was set in a period we now recognise as the birth of Australian batrachology. Never before had such intensive studies of Australia’s frogs been attempted. Murray, Bill, Bob and notable others were trailblazers whose work represents the bedrock of what has grown to be a rich and diverse science. But that moment has other significance, for it was just prior to a calamitous event that would have sweeping impacts on Australian amphibians. That event — which extirpated the glorious green frogs of Upper Plenty and much of the Southern Tablelands — was the arrival of amphibian chytrid fungus in eastern Australia.

Chytrid fungus is the worst wildlife pathogen the modern world has known. In Australia, it brought millenia of evolution to a shuddering holt for 7 species, driving them into the abyss of extinction. Others went to the brink, where they remain, propped up by dedicated souls. But even those that seem to have stabilised remain profoundly affected, with diminished ranges and narrower habitat affiliations than the ones they showed before chytrid arrived. They are in an environmental stand-off with the pathogen. But why exactly?

This is a complex question to answer, but one possible reason is that populations surviving with chytrid fungus are those that can persist by offsetting higher adult mortality through other demographic mechanisms. In a recent study, myself, Ben Scheele, Michael Scroggie and Matthijs Hollanders set out to assess how such demographic mechanisms can enable persistence of frogs afflicted with endemic chytridiomycosis. We focussed on Southern Bell Frogs (SBF) and Green and Golden Bell Frogs (GGBF), knowing that the pioneering work on these frogs in the 1970s could provide powerful insights into how their demography has changed due to chytrid, and the conditions in which persistence is possible despite these profound impacts.

And so, we took ourselves off to the Museum. With the help of curators at the Melbourne Museum, the Australian Museum and the CSIRO National Wildlife Collection, we tracked down pickled SBFs and GGBFs that had been collected before chytrid arrived in Australia. We sought out specimens that were collected at sites close to those at which we’d worked on persisting populations of these frogs — Melbourne’s northern plains (a stone’s throw from Murray and Bill’s swamp at Upper Plenty) and the Southern Tablelands of NSW. We took bone samples from each specimen by removing one of their toes, just as we’d done during our contemporary sampling. And with that, we had matched bone samples from these areas pre- and post-chytrid, which we could use to age each frog and compare longevity and survival rates before and after the fungus arrived. We did this by counting lines of arrested growth (LAG) in bone cross sections, which are laid down during the winter torpor period (consider LAG the frog eqivalent of tree rings). The process is known as skeletochronology.

Sure enough, our matched bone samples revealed that the age structure of Bell Frogs is significantly truncated in remnant populations, with few frogs living for more than two years today, while historically a considerable proportion lived to four years of age or more. Using a fancy statistical approach developed by Mike Scroggie, we estimated that adult survival rates in remnant populations are 50% lower than prior to chytrid’s arrival.

Using this information as a basis, we then set about using metapopulation simulations to understand how this drop in survival rates constrains where these frogs can and cannot now live. We ran simulations of metapopulation trajectories varying fecundity rates (representing variation in habitat quality), annual variation in fecundity and survival rates (representing environmental stochasticity) and the number and proximity of habitat patches within a landscape (representing both habitat availability and connectivity). These simulations revealed that among the many combinations of these parameters, contemporary metapopulations of these frogs — with their depressed survival rates due to chytrid — could persist in much smaller zone of the parameter space than was historically the case. To survive, contemporary metapopulations needed high habitat quality (i.e., very high fecundity), low environmental stochasticity (low variation in fecundity and survival) and high habitat availability and connectivity. In short, our simulations revealed that chytrid has shrunk metapopulation viability for SBFs and GGBFs, to landscapes in which demographic resilience is at its highest — those with lots of top-quality habitat that provides fairly predictable conditions from one year to the next.

Of course, this all makes perfect sense and aligns with other studies on chytrid impacted frogs in Australia and elsewhere. But what this study contributes is a deeper understanding of the demographic mechanisms of persistence, and ultimately the environmental variables that underpin these mechanisms. In doing so, it gives us insights into the patterns of range contractions that Australian frogs have shown following the arrival of chytrid fungus to our shores, and it can be used to guide management to secure remnant populations. As we explain in the paper, if we can implement management that increases habitat availability and connectivity, increases recruitment rates and moderates the impact of environmental variation (like rainfall and temperature variability delivered by cycles of El Niño and La Niña), then we stand a good chance of enabling these populations to withstand chytrid-related mortality. Think of it this way — we can make these frogs resistant to the fungus, but through demographic levers, not immunological or evolutionary ones.

Ultimately, the hope is that the coming generations will be able to experience the extraordinary phenomena that Murray Littlejohn, Bill Sherwin and Bob Humphries experienced in the 1970s. I revel in the thought of future herpetologists wading through the wetlands of south-eastern Australia amid a cacophony of Bell Frogs. If we support them to out-breed chytrid and overcome the demographic hit from other threats — though habitat protection, enhancement and creation — we can make this a reality.

Burnt rainforest is a surreal landscape. To get the full effect, first picture yourself immersed in the deepest rainforest to which your imagination instinctively takes you. Towering Figs whose massive canopy is home to myriad lichens, lianas and epiphytes. Palms of effervescent green jostling for the sun. Luxuriant mosses and hypercolour fungi carpeting fallen timber on the forest floor. Crystal clear water gurgling down cobble-lined seeps. Deep leaf litter of golds and yellows, saturated from the rain and mists that daily sweep the forest.

Now, strip that same landscape of colour. Replace the greens with muted browns and greys. Erase the moss and fungi, and substitute the leaf litter for exposed, desiccated clay. Kill the palms, whose fronds hang limp, and sprinkle charcoal around the buttress roots of the now dead Figs. Swap the crystal-clear seeps for eroded gullies filled with silt and ash.  

It is a confronting image, and one I personally couldn’t comprehend until I saw it with my own eyes. We were in the Main Range in south-east Queensland in September 2020; the first Spring following the devastating Black Summer fires that raged across eastern Australia in 2019/2020. Our purpose was to survey for an endangered rainforest frog that is one of many endemics of the Scenic Rim. On this particular day I was following Queensland’s frog champion-in-chief, Harry Hines, along a winding track through wet sclerophyll forest that was burnt severely by the fires the year before. Soon we reached the rainforest, where those extraordinary fires had punched deep into the normally fire-proof vegetation. While severe, the burns in the wet sclerophyll forest hadn’t shocked me – sclerophyll forest burns, that’s why it is what it is. But rainforest? Fire kills rainforest, right? I felt I was witnessing the start of the end for these particular remnants. Remnants that had survived for millennia, in climate refugia that themselves felt on the cusp of disappearing.

Our surveys that day were part of a wider effort to understand the impact of the Black Summer fires on threatened frogs. This particular project – funded by the NSW Government’s Saving our Species Program and the Australian Government’s Threatened Species Recovery Hub and Commonwealth Bushfire Recovery Program – focussed on the Mountain Frog (Philoria kundagungan) and two closely-related species, the Richmond Range Mountain Frog (Philoria richmondensis) and the then not-quite-described Mount Ballow Mountain Frog (Philoria knowlesi). A major aim was to re-survey sites for P. kundagungan and P. richmondensis that have been the focus of David Newell’s research group for some years, to enable comparison of occurrence and abundance post-fire with that observed pre-fire. My contributions to the field work were admittedly meagre, with the great majority completed by Harry and his team, and the monumental efforts of Southern Cross University’s Liam Bolitho.

My primary task, assigned to me by project co-lead Ben Scheele, was to analyse the resulting data and write up a report and paper describing the outcomes. Fast forward to today and that paper has finally been published. You can find it here.

So, what did we find? I’ll focus on the two species for which we obtained the most data. For P. kundagungan, we estimated some 30% of potential habitat for this species was burnt, and the data provided evidence of important effects on fire and the associated drought conditions on occupancy rates and abundance of calling males. Occupancy rates were down 19% from surveys in the 2016/2017 breeding season, and sites that were burnt were significantly less likely to support calling males post fire (as were those that remained drought affected). For the P. richmondensis, only 12% of potential habitat was burnt, and we did not find clear effects of fire on occupancy or abundance of calling males post-fire (in part, because much of the habitat that was burnt was in lower elevation areas that are generally less suitable). Like P. kundagungan however, there was clear evidence for drought impacts on this species, with important effects of site saturation extent on occupancy and abundance. Moreover, compiling the data for all survey seasons for this species (2012/2013, 2019/2020 & 2020/2021) showed that occupancy rates and abundance were significantly depressed immediately prior to the Black Summer fires when drought was at its zenith, but recovered somewhat in 2020/2021 following significant winter rainfall across the range of this species. Not surprisingly, drought significantly curtails breeding attempts in this species, which relies on saturated seeps in which to build its nests.

Three years on, spurred by a triple La Niña , the burnt rainforests of the Gondwana World Heritage Area are starting to recover. Their colour has returned, with a flush of new growth obscuring the more obvious signs of the fires. What’s more, evidence has accrued of the resilience of these systems to fire incursions; greater resilience than we once thought possible. These are encouraging signs, but studies such ours and myriad others on the impacts of the Black Summer fires, show that these blazes and the preceding intense drought will have a lasting impact. And we know from climate forecasts that intense droughts and resulting wildfires will threaten these landscapes again in the coming decades, perhaps repeatedly. So, we must prepare. For species like Philoria, we need to increase their resilience by reducing other threatening processes, like feral pigs, which destroy the fragile hydrology of their nesting sites and may prey directly on the frogs themselves. We can also minimise the risk of fire incursion to their rainforest seeps by careful management of fire in neighbouring habitat, and stemming the invasion of flammable weeds. And we can take direct action to respond when these steps aren’t sufficient, by establishing captive populations and pursuing releases to re-establish populations when they blink out, or reinforce populations weakened by fire or drought. In an exciting development, this is exactly what is being pursued by Dave Newell’s team at Southern Cross University, with support by the NSW Government’s Saving our Species Program.

Until the world curbs its CO₂ emissions, conservation of many rainforest endemics will need to focus on these local scale actions. The overarching threat is ominous, but we do have levers to pull to bolster the resilience of exposed populations. Success will depend on the scale of investment, and – as always – plenty more of that is required.

This profile piece originally appeared in the Autumn 2022 newsletter of the Centre for Biodiversity and Conservation Science at the University of Queensland, which I’ve recently joined as an Affiliated Researcher

Mum likes to remind me that I’m a worrywart. It’s true, I am. But it has only recently occurred to me that my passion for threatened species — now extending back well over two decades — may ultimately stem from this character trait. I worry about our threatened species because they are, by definition, in trouble. Maybe they have their own inherent frailties; maybe they can’t compete with some whizz bang new invasive; or maybe we humans have a penchant for their particular habitat. Whatever the case, they are imperilled, and my worrywart radar is triggered.

The upside is that constructive worrywartism — how I describe my own particular affliction — motivates action. One of the key ways the constructive worrywart is pacified is through identifying solutions. And so, for threatened species, my inner worrywart wants action. It asks, rather incessantly, “What can we do for these species?”. Thankfully the answer is ‘lots’ in most cases; we just need to work out what. And that, in a nutshell, describes my career to date.

From La Trobe to the University of York

I grew up in Melbourne’s northern suburbs, and after a decade filling Mum’s shed with pet snakes, took myself off to complete a Bachelor of Biological Sciences at La Trobe University (inexplicably missing Prof. Martine Maron, who was there at the same time doing the same subjects). I focussed on Zoology, and on completing my undergrad had the great privilege of joining a radio-tracking study of threatened Inland Carpet Pythons for my Honours. From there, I worked as an ecological consultant for three years, before starting a PhD on Growling Grass Frog conservation, again at La Trobe. It was heady days, and for a time I even shared a house with Dr Simon Hart and Prof. Eve McDonald-Madden.

With my stay at La Trobe drawing to a close in 2009, I sought to continue my work on GGFs as a postdoc. I collaborated with Prof. Kirsten Parris and Prof. Michael McCarthy at the University of Melbourne to win an ARC Linkage Grant and spent the subsequent 3 years building a metapoplation model for the species. The work culminated in the use of our model by the Victorian Government to prioritise ~$60M of habitat creation works for GGFs across Melbourne’s urban growth zones; just the outcome I hoped for.

In 2013, I was awarded a Victorian Postdoctoral Research Fellowship and travelled to the University of York to study at the knee of Prof. Chris Thomas. These Fellowships had tight eligibility criteria around ‘Victorianess’; one was almost ineligible for the mere thought of straying across the border. And so myself and several other conspicuously insular Victorians were sent overseas to broaden our minds, make international connections and return to the antipodes with a bevy of papers. It was a terrific time, and one for which I partly have Prof. Hugh Possingham to thank – the final year of this fellowship was supported by the ARC Centre of Excellence for Environmental Decisions (CEED), so thanks Hugh!

To TERN and the TSX, with a few steps in between

After my VPRF, I secured a Lectureship at Charles Sturt University in Albury teaching Wildlife Ecology and Management, but after a happy two years, career opportunities in Melbourne were calling us back. My wife Tanja joined the University of Melbourne and I fell in with the Arthur Rylah Institute for Environmental Research, spending two years with them as a Senior Scientist working on such things as Koala abundance estimates and PVA models for species impacted by windfarms. And then came the bombshell – Tanja secured a Senior Lectureship at Griffith University in late 2019, and we were off to Queensland. We crossed the border the day it closed — 25^th March 2020.

My first 18 months in Queensland were spent working freelance on ecological modelling studies, with a 6-month stint with the TSR Hub working on bushfire impacts on rainforest frogs (under Dr Ben Scheele at ANU). Then, in August 2021, the Project Manager position for the Threatened Species Index (TSX) was advertised and I hurried to submit an application before going on a month-long herping trip around Queensland. I did the interview from a motel room in Mackay and was offered the job the following day. I joined TERN and UQ in November 2021, to my great delight.

The TSX

You could be forgiven for thinking that being the Project Manager for the TSX is not the ideal position for a worrywart. Most ways you cut the data, the TSX shows that our threatened species continue to decline. Yet the TSX is a terrific fit for me, because it is a powerful tool to stimulate action for our threatened species. When it produces graphs showing falling abundance, it demonstrates clearly that we must do more. When it produces graphs that show stable or even increasing abundance, it shows us that we can succeed. And it can even show us why we are failing or succeeding; it gives us insights into which actions work and which ones don’t. And so my inner worrywart — constantly nagging me about what we can do for our threatened species — is satiated. It knows I’m helping to answer the question, and that conservation actions will follow.

Cold, wet, exhausted. It’s 2AM and you’re 1000 m up a rainforest ravine in the Wet Tropics. You’re finally horizontal, but your hammock – saturated and starting to smell of mildew – offers little prospect of sleep. Outside, in the pitch black, the stream you’ve been relentlessly climbing cascades over boulders that it has been wearing down for millennia. But over the white noise of water on granite, you can hear a frog calling “wreek wreek wreek”. It’s the Common Mistfrog, and you’ve just detected the species high atop the jungle-clad Mt Lewis. In the process, you’ve confirmed that this species is winning the battle against chytridiomycosis, reclaiming a footing in the upland rainforests from which it disappeared two decades earlier.

This tale – which sounds straight out of the choose your own adventure novels I devoured as a boy – was Sara Bell’s reality in 2013. Sara, then a postdoctoral fellow at James Cook University, was on an audacious mission to climb five rainforest streams across the Wet Tropics in search of frogs. Under the guidance of Lee Berger and Lee Skerratt, Sara was seeking to document the contemporary elevational range of four species in particular, each of which had each been knocked out of the uplands when chytrid fungus invaded during the early 1990s. Sara’s study sought to assess the degree of recovery in these species. Were they still stuck at low elevations, in the warmer environments in which chytrid is both less prevalent and less virulent? Or had they managed to recolonise environments higher up, where the cooler conditions better suit chytrid and constrain the immune system of their ecothermic hosts?

Our latest paper answers these questions, and several others. In 2016, I came onboard Sara and ‘The Lees’ ambitious project, being called upon to help crunch the resulting data. Sara had amassed not just records of where frogs were and were not detected on her epic elevational transects, but with the assistance of several crazy-brave assistants, had swabbed frogs for chytrid up and down the mountains, and placed out air and water temperature loggers to monitor the microclimate at each 200 m elevation step. My job was to quantify the patterns of infection prevalence and intensity, link these to the microclimatic variation across the elevational gradient, and assess the correspondence between chytrid prevalence and the contemporary distribution of each frog species. With such a hard-won and significant dataset already amassed, I was an easy recruit.

Sara risking life and limb for science. Waterfalls be damned!

What Sara’s data reveal is that three species appear to be winning the battle against chytrid. The Common Mistfrog (Litoria rheocola) was found up to 1000 m above sea level, the Waterfall Frog (L. nannotis) was found up to 800 m asl and the Green-eyed Tree Frog (L. serrata) was found up to 1200 m asl. Each was previously known from up to or above 1200 m, but dropped out of high-elevation monitoring sites as chytrid swept through in the 1990s. Hence, the data suggest recolonisation is well underway in some locations, which in turn suggests that these three species have developed some resistance to chytridiomycosis. The additional data Sara collected give us insights into the extent to which this has occurred. They show that chytrid still appears to constrain the distribution of two of these species – L. rheocola and L. nannotis – with a strong negative relationship between mean monthly temperature and chytrid prevalence, and a negative relationship between chytrid prevalence and the probability of occurrence. Hence, chytrid prevalence increases as elevation increases (due to cooler temperatures at higher elevations), and the highest elevations are still not quite attainable for these species as a result. In turn, we can surmise that whatever mechanisms of resistance these frogs are evolving, they have not yet fully overcome the environmental determinants of chytrid virulence that produced the elevational decline in the first place. The frogs are still struggling in chytrid’s environmental hitting zone, and recovery is a work in process.

But what about the third species that has shown signs of recovery, L. serrata? Well, Sara’s data suggest this species is effectively now reached ‘chytrid normal’ (to steal a COVID analogy). This species displayed a high prevalence of infections (47%) and there was no attenuation of infection loads, meaning frogs were just as likely to have heavy infections as light infections. Both are patterns we see in species that are asymptomatic to chytrid – lots of individuals are infected and some have high burdens, but chytrid has lost its killing power. Indeed, we found that the probability of occurrence of L. serrata actually increased with predicted chytrid prevalence, with the host and the pathogen sharing a similar preference for higher, cooler and wetter rainforest. Chytrid can no longer control this species’ distribution, and its been freed to reclaim the deepest, darkest jungle that it always preferred.

Rainforest glamping? Not at 1000 m up a ravine, with blood oozing from myriad leech bites, battered shins and little more than gluggy porridge awaiting for breakfast.

Now, observant readers are wondering about the fourth species on Sara’s list of targets. Well, the data suggest that this species – the incredible Australian Lacelid (Litoria dayi) – remains in chytrid’s thrall. Sara didn’t detect the species above 400 m asl – under half its known elevational range pre-chytrid. Furthermore, only two individuals swabbed had the pathogen, and infection loads were low in these two frogs. In short, L. dayi is persisting in lowland refuges away from chytrid’s full impact. It does not appear to have gained any tolerance for the pathogen, and remains stuck in lowland environments where the likelihood of infection – and particularly getting a fatal infection – is low.

So, what does this all mean for our understanding of chytrid impacts in Australia, and management of frogs threatened by it? First, our study provides further evidence that some frogs that took a strong initial hit from chytrid are starting to recover, as has been witnessed in two other Australian species, one of which is the threatened Fleay’s Barred Frog (Mixophyes fleayi). Second, our study shows that environmental refuges – areas in which the prevalence and/or virulence of chytrid is relatively low – have been crucial to the persistence of these rainforest frogs, as has habitat connectivity, which has facilitated recolonisation as resistance has developed. This reliance on environmental refuges and habitat connectivity mirrors the situation for my beloved Growling Grass Frog (Litoria raniformis) and its sister-species, the Green and Golden Bell Frog (Litoria aurea). Third, our study reveals that some species will remain restricted to environmental refuges, even while other species recover, and this may lead to both a permanent change to the species’ niche and a heightened conservation focus on protecting these crucial refuges. Fourth, the work lays the ground-work for attempts to hasten recovery of the target frogs. For example, among Sara’s target species, translocation to unoccupied sites could be pursued for L. dayi and L. nannotis, both of which were not detected at streams from which they were historically known – they appear to have been knocked out entirely by chytrid along these streams, and have no capacity to naturally recolonise them, being separated from remnant populations by cleared land. Sara’s work has shown that these frogs could survive in lowland sections of these streams, and L. nannotis could push back up into the uplands, particularly if the founding individuals were taken from recolonised upland sites, where some form of resistance is likely to have developed.

Chytrid impacts remain a key challenge for Australian frog conservation, with some species still losing the battle. The Southern Corroboree Frog and Baw Baw Frog, for example, remain in dire straits. However, positive news is accruing, and Sara’s study adds to this story. The work shows that natural recovery is underway for some frogs hit hard by chytridiomycosis, and that there are tangible options to both facilitate recovery and shore-up refuge populations. Gone are the days of hand-wringing about our incapacity to tackle this threat. Sara’s study is one of a several to show that when we gain an understanding of the pathogen, and host responses to it, management actions are revealed. We now find ourselves in a real-world ‘choose your own adventure’ – we need to experiment with alternate management actions, and find the combination that produces the happy ending we all so desperately want for these frogs.

I suspect I’m one of many for which the predictability of species distributions was a gateway drug to ecology. My journey began with an extraordinary biogeographic transition point, delimited by the sheer slopes of the Plenty Gorge on Melbourne’s northern outskirts. East of the river – where I grew up – was a world of Yellow Gum, Red Box, Wattle and Cassinia. Undulating mile upon undulating mile of it, built on sedimentary soils laid down during the Ordovician. The plains west of the Plenty River were a very different landscape. Volcanic epochs transformed this country, laying deep basalt clays over the underlying sedimentary rock. Kangaroo and Wallaby Grass, Spear Grass and Poa grew here in prolific stretches prior to European settlement, and gave rise to a markedly different faunal assemblage to that east of the Gorge.

As a young fellow, this biogeographic divide enabled an idea to crystallise in my mind. If I could grasp the geological, climatic or floristic affiliations of species, I could always find them. Little Whip Snake? West of the river, on cracking clay soils under exfoliating basalt. Weasel Skink? Rotting leaf litter or timber in damp gullies east of the river. Jacky Dragon? Cassinia and Acacia dominated heathlands on the steeper banks of the Gorge, where protruding mudstone reefs dominate. These were rules, as good as the laws of thermodynamics – learn them, and you have each species pegged.

But what if you don’t? What if these rules can change? What if much of what you have learnt about a species can go out the window in a metaphoric blink of the eye? Welcome to the concept of the ‘dynamic niche’, where biotic shifts can drastically reshape the distribution, habitat affiliations, demography and even evolutionary trajectory of species.

Over recent decades, amphibian ecologists have been confronted with rapid niche shifts of this kind. The driver has been the emergence and spread of the pandemic lineage of chytrid fungus. The headline grabbing impacts of this pathogen have been wholesale extinction events and drastic population declines. But another, more subtle phenomenon has also emerged – changes in the ecology of many frogs, some of which now appear quite irreversible. Our most recent paper, led by Ben Scheele, is an attempt to describe these shifts, to synthesise the patterns therein, and to guide conservation responses for species that appear permanently changed by their interactions with this pathogen.

Two frog species from Australia’s south-east are useful exemplars. The first is my beloved Growling Grass Frog, a species that was both abundant and widespread prior to the arrival of chytrid to Australia’s east coast in the late 1970s. Through the 1980s and 1990s, the species experienced drastic population declines, collapsing out of the areas that were environmentally most suitable for the pathogen – colder and/or wetter parts of the range, such as higher-elevations, frost-ridden plains and wetter foothills (see figure below). Habitat affiliations of the frog also appear to have narrowed, to wetlands that are relatively warm and/or slightly salt-affected (conditions in which the pathogenicity and virulence of chytrid is reduced). No longer can they persist in the cooler, fresher sites in which they once thrived, nor those that dry out with any frequency. The Growling Grass Frog we know today is a different beast to the frog we knew prior to 1978.

Changes in the distribution and realised niche of the Growling Grass Frog due to chytrid. The map shows records of the species up to 1980 (orange) and subsequent to 2000 (green), broadly representing the pre- and post-chytrid distribution. The plots show the change in the elevational and thermal niche of the species, resulting from its distributional contraction.  Figure 2 from Scheele et al. (2019), Biological Conservation 236, 52-59. © Elsevier.

Likewise, the Alpine Tree Frog has been changed dramatically by the arrival of chytrid. A once fairly long-lived species (up to 7 years), today it rarely lives beyond 2 years of age. Early reproduction is now imperative, and there is evidence the heavy selection for early reproduction is altering the life history traits of this species. Habitat affiliations are also shifting, because consistent recruitment is now utterly vital for persistence at the population level (with adult survival so low, even a single year of reproductive failure can spell doom for isolated populations). As a result, the species is dropping out of the ephemeral wetlands systems that were once prime breeding habitat, and it is increasingly affiliated with permanent or near-permanent wetlands.

As well as highlighting the ecological impacts of chytrid, these two species are useful for demonstrating the shift that conservation managers must make in their approach to species with endemic chytrid infections. Take re-introduction to former haunts, which is often proposed as an approach to conserve these frogs and many others. Such initiatives will fail miserably if chytrid has the upper hand at the target locations. Indeed, we’ve seen this for another Australian hylid for which re-introduction has been attempted numerous times – the Green and Golden Bell Frog. Most re-introductions have failed, often as the frogs were put into habitat with characteristics that they used to be affiliated with. Ultimately, these re-introductions failed because we, as amphibian ecologists, failed to recognise the new world order for these frogs.

For more on the topic, you can find the paper here (or email me for a copy if you can’t get through the paywall). It is a thought-provoking, challenging and perhaps even controversial concept, but one we must consider for effective amphibian conservation in the post-chytrid era. Nevertheless, the parallels with invasive species impacts and wildlife diseases more generally are clear, and so we hope the paper will prove of interest beyond the realms of amphibian conservation. Niche shifts are happening across the globe, and we must be alert to them if our conservation initiatives are to remain effective.

Road trips of my youth rarely entailed music. My siblings and I cruised the highways of south-eastern Australia mostly in silence. Melbourne to Bright – silence. Melbourne to Barmah – silence. Melbourne to Canberra – silence. Melbourne to Mildura – silence.

It wasn’t enforced – I didn’t grow up in some sort of ‘Footloose’ inspired cult family in which the revelry of music was considered sacrilege. My father, who was invariably driving, merely preferred quiet contemplation and the joy of the drive. Or at least that’s what I presume; the truth is I’ve never actually asked.

Whatever my father’s motivations, the outcome for me was profound. Our family holidays were invariably north, away from Melbourne to more xeric climes. We wandered the Hume, the Calder, the Northern and the Newel, seeking out rivers and lakes across the great expanse of the Murray-Darling Basin. From the cool mountain streams in the upper catchment, to the languid lower reaches of the Murray and Darling Rivers themselves. The thing is, as you cruise through these landscapes in silence, you take more in. You notice the change from White Box to Grey; the first appearance of Buloke; the disappearance of Cassinia and the appearance of chenopods. You absorb the landscape, subtly and osmotically. As the kilometres fall away, the great tapestry of biogeography is revealed.

Take Triodia. My first sighting of this extraordinary grass remains etched on my mind. Triodia – or Spinifex as it is more commonly known – is perhaps the singular success story of the Australian Outback. It occurs over literally millions of hectares of the most arid and desolate terrain Australia has to offer. My fascination with this grass is not (I must admit) with it per se, but rather with the animals it houses. For Triodia hummocks are a remarkable store of lizards. You may know that Australia’s deserts have some of the highest densities of lizards in the world, both in terms of abundance and species diversity. You may not know that Triodia is a key driver of this, at least according to some. Its hummocks provide seemingly perfectly designed lizard lairs, complete with a protective shroud of spiny foliage, cool and stable microclimates and an abundance of juicy invertebrate prey.

It was somewhere around 20 km north of Ouyen in the Victorian Mallee where I caught my first glimpse of Triodia. We’d been driving up the Calder Hwy for hours – probably five by that stage – on our way to Mildura. I’d been watching the vegetation change from tall forest to Box-Ironbark to Mallee, through various shades that entailed evermore diminutive Eucalypts. Now we were approaching proper sand dunes, and I knew that Triodia was on the cards. Then, sure enough, on cresting a dune of previously unrivalled proportions, there it was. A hummock. A Spinifex hummock! In the flesh, whizzing past my window. I craned my neck and watched it until it disappeared from view.

Whipping back, I looked for more. It took time, perhaps another 5 km, and then I spotted another. Then another and another, until they were carpeting the ground. We’d hit Hattah-Kulkyne National Park and the blessed things were everywhere.

To this day, I think about that sole hummock, a good 5 km from its nearest brethren. Was it the most southerly hummock in that region? If it wasn’t, then such a hummock must have existed, out there, somewhere. And if that is true, then it is also true of every species in the world. All must have one individual, at any one point in time, that is the most far flung member of its species. One intrepid individual pushing the limits of the species’ range. What drives these boundaries? What holds them in place? Is it thermal tolerances, or geological affinities, perhaps a deep-seated fear of frosts or some symbiont that a species just can’t do without?

Ultimately, what I learned on those long, silent drives with my family is that this intrigue is eternal. Australia’s biodiveristy is immense and all species respond to environmental gradients uniquely. And anyway, ecosystems are forever changing and species distributions along with them. The search for biogeographic truths is endless, and it will always be so.

Last week myself and colleagues from Charles Sturt University, Deakin University and the University of Queensland wrote a piece for The Conversation arguing that the role of Australia’s Threatened Species Commissioner should be strengthened and made independent from government. It is a timely piece – the first Commissioner recently stepped down and his replacement is currently being sought. It represents an important moment to reflect on the successes and failings of the role so far, and ways it could better serve Australia’s diverse and precious biodiversity.

You can read the article in full here.

How does one control a rapacious pathogen? If it were an infectious agent of humans, we would have much in our armoury. We could isolate the stricken, and slow the pathogens spread. We could search for the vector and extinguish it. We could take antibodies from the immune and treat the susceptible with their serum. Or we could disseminate doses of powerful antibiotics or vaccines, and lead the pathogen down the path to functional extinction.

But what if the pathogen targets wildlife? In that case, our armoury is much diminished. So much so that the outcome of wildlife-pathogen interactions in nature is almost always determined by natural mechanisms; death of the vulnerable and, failing complete extinction, either survival and proliferation of the immune or the recovered, or persistence of susceptible populations in refugia, away from reservoir hosts or in regions outside the pathogen’s environmental hitting zone.

In our latest paper, just out in Conservation Letters, we assess the degree to which knowledge of environmental refugia can be used to mitigate the impacts of perhaps the worst wildlife pathogen of modern times – the amphibian chytrid fungus. Chytrid emerged as a major pathogen of amphibians late last century, for reasons unknown. It spread across the globe, facilitated by us, and decimated frogs and toads as it went. The toll is difficult to quantify (and continues to mount), but at least 200 species are now thought to have either succumbed completely to chytridiomycosis, or suffered significant population declines.

Chytrid sporangium, CSIRO

Despite this, chytrid is not invincible. In fact, it has some key environmental frailties – its pathogenicity falls sharply at warmer temperatures, and it cannot tolerate acidic or alkaline environments, nor those which are somewhat saline. In short, it has several environmental Achilles heels.

We set out to assess the degree to which these weaknesses could be harnessed to bolster amphibian population viability. For small metapopulations of our focal species, the threatened Growling Grass Frog, we used simulations to understand how slight increases to wetland water temperatures and salinity (achieved by reducing wetland shading, increasing wetland size and depth, and tapping groundwater) could reduce pathogen prevalence and increase rates of frog population persistence. In addition, we assessed the degree to which strategic creation of warm and slighty saline wetlands (<10,000 µS/cm) could enhance metapopulation viability. The work builds on our 2015 paper which demonstrated that environmental refugia, metapopulation size and connectivity are important determinants of the persistence of Growling Grass Frog populations afflicted by chytrid.

So, what did we find? Three things in particular. First, our simulations suggest that habitat management to mitigate chytrid impacts will be most effective in climates where hosts are already less susceptible to the disease; that is, within climatic refugia where disease impacts are already curtailed. Second, our work suggests that creating new wetlands with refugial properties may be substantially more effective than manipulating existing habitat, in part because altering existing habitat will be constrained by other environmental considerations. Third, increasing metapopulation size and connectivity through strategic habitat creation can greatly reduce extinction risk, because dense-clusters of wetlands are much more likely to enable a balance between the opposing forces of population extinction and (re)colonisation.

Our work is one of very few to assess the effectiveness of habitat-based management levers for controlling wildlife disease. The results are encouraging. The next step is to test the effectiveness of habitat-based management of chytrid in the field. We need well-designed, statistically rigorous experiments replicated across multiple taxa to understand the scale and breadth of its effectiveness, its practicality under varying contexts, and the cost-benefit ratio relative to other potential control options.

A pool on the Merri Creek recently choked by invasive Phragmites, Willows and Hawthorn. Once an important breeding site for Growling Grass Frogs, the species is no longer found here

But in the interim, our work provides clear guidance to managers of Growling Grass Frogs in southern Australia, and its sister-taxa the Green and Golden Bell Frog and Yellow-spotted Bell Frog. The niche of these frogs has narrowed in the wake of chytrid. Today, they require dense networks of wetlands that receive copious sun, and they can benefit from slightly saline environments. If shading from riparian trees and invasive emergent vegetation is prevalent in the systems you manage, thin it out or remove it all together. If wetlands are sparse, small and shallow, seek to build adjacent wetlands which are large, deep and unshaded, providing not just disease refugia, but bolstering metapopulation size and connectivity as well. And if you have access to slightly saline ground water (<8,000 µS/cm), consider sinking bores and feeding some wetlands with this water source.

Do let us know how you get on.

We humans live in perpetual fear of epidemics. Some nasty new bug emerging from the jungle, sweeping across humanity and knocking off millions of us in the process. Or perhaps an existing pathogen that mutates into a superbug capable of spreading like wildfire, transmitted by as little as a dirty look.

While sometimes bordering on irrational (cheers Hollywood), our fear of epidemics is well placed. We’ve had some doozies in the not too distant past. Take Spanish Flu – a disease that killed somewhere between 50 and 100 million people between 1918 and 1920, reducing the world population by up to 5%. What’s more, our spine-bearing brethren give us regular reminders of the ruinous power of pathogens. Examples include white-nose syndrome in bats, avian malaria, Parapoxvirus in squirrels and the recent implosion of Saiga populations on the Eurasian steppe.

In the wildlife realm however, one disease stands head-and-shoulders above the rest as a potent reminder of the destructive capacity of pathogens. Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis, has killed literally millions of frogs across the globe over the last four decades, driving thousands of local extinctions and either major decline or global extinction for up to 200 species. A truly remarkable feat for a single pathogen. In Australia, chytrid hit in the late 1970’s, arriving first (we believe) in Brisbane, before heading north and south along the east coast, and skipping across to Western Australia and Tasmania. It left carnage in its wake. Frogs that were formally abundant and readily found simply disappeared. Apart from a few observed die-offs, numerous populations went up in a figurative puff of smoke. Seven species met their doom.

Our most recent paper reviews what happened next. Led by the inimitable Dr Ben Scheele, the paper draws together published and unpublished data to review the fate of Australian frogs impacted by chytridiomycosis following the initial epidemic. We detail the varying responses of these species, ranging from ongoing decline, to stabilisation and even recovery. Furthermore, the review draws together the known mechanisms underpinning these responses, which Australian and international herpetologists have steadily revealed over the last two decades.

The news is mixed. Chytridiomycosis remains the chief threat to several highly endangered frogs in Australia, such as the Southern Corroboree Frog and Baw Baw Frog, both of which may soon no longer persist in the wild. However, others have stabilised and some have even clawed back formerly occupied territory. Encouragingly, the latter may be on-route to full recovery. The review also highlights that we now know enough to trial management options for some species. For example, it may be possible to target reintroduction efforts to habitats with few reservoir hosts of chytrid, or we may be able to manipulate the environment in ways that gives susceptible frogs an epidemiological or demographic edge over the fungus (a topic on which my own research has focused in recent years).

With that, I commend the paper to you. As always, if you’d like to read the paper but can’t get through the paywall, drop me an email and I’ll send it through.