New paper: Connectivity over a disease risk gradient enables recovery of rainforest frogs

ejytbgcu8aaey1wCold, 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-on-creek-1  2013_05_22-19

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.

2013_05_23 (1)Rainforest glamping? Not at 1000 m up a ravine, with blood oozing from myriad leech bites, battered shins and little more than re-hydrated 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.

The dynamic niche

A0216_L_raniformisI 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.

Lessons in biogeography (from the back seat of a Datsun station wagon)

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 mutualist that a species just can’t do without?

Ultimately, what I learned on those long, silent drives with my father is that this intrigue is never ending. 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.

Australia’s species need an independent champion

img_1196Last 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.

New paper: Can habitat management mitigate disease impacts on threatened amphibians?

swabbingHow 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.

2016 Herping in review

Between 2013 and 2015, I was lucky enough to embark on an ecological odyssey to the UK. With backing from a Victorian Postdoctoral Research Fellowship, I set off for the University of York and spent a happy two years learning at the knee of Prof. Chris Thomas. Through daily chats with Chris, and the other great folk that called York’s J2 lab home, I gathered a sense of the incredible biodiversity data sets that UK ecologists have at their disposal. The British populace, I soon realised, are just as fanatical about collecting biodiversity data as they are about train spotting, building model aeroplanes and tracking down obscure antiques. From immense observational data sets, to comprehensive, statistically-rigorous monitoring programs, the Brits produce masses of species occurrence and abundance data every year. I was hugely impressed; not just with the British fervor for good, solid data, but the end products too – great ecological science and perhaps an unrivaled capacity to monitor the country’s biodiversity.

Returning to Australia, I had a new found sense of the importance of maintaining records of the species I see in my travels. Specifically, time-stamped occurrence data, the sorts of which are vital to producing species distribution maps and models, and which, in the long-term, can provide insights into population declines, range shifts or even invasions. I’ve been diligently keeping these records ever since, with annual uploads to the Victorian Biodiversity Atlas and the Atlas of Living Australia.

So, what of 2016? In all, I managed 126 records of 53 species, with observations from the tropical forests of North Queensland, through southern Queensland, New South Wales and into the hills and plains of Victoria. I met numerous new species, including Scrub Python, Jungle Carpet Python, New England Tree Frog, Striped Burrowing Frog, Golden Crowned Snake, Cascade Tree Frog, Sudell’s Frog, Rugose Toadlet and Red-eyed Tree Frog. The full species list can be found in the table that follows, with further details here. I also had the opportunity to photograph many of the species I encountered this year, having finally managed to save enough pennies for a decent digital camera. I’ll leave off with a few of the images I captured (you can head over to my Flickr page if you would like to see more).

Species list:

Species Common Name
Amalosia lesueurii Lesueur’s Velvet Gecko
Amphibolurus muricatus Jacky Dragon
Boiga irregularis Brown Tree Snake
Cacophis squamulosus Golden Crowned Snake
Carlia tetradactyla Southern Rainbow Skink
Chelodina longicollis Common Long-necked Turtle
Christinus marmoratus Marbled Gecko
Concinnia martini Martin’s Skink
Crinia parinsignifera Plains Froglet
Crinia signifera Common Froglet
Cryptoblepharus pannosus Ragged Snake-eyed Skink
Ctenotus spaldingi Robust Skink
Ctenotus taeniolatus Copper-tailed Skink
Cyclorana alboguttata Striped Burrowing Frog
Delma impar Striped Legless Lizard
Diporiphora australis Tommy Roundhead
Egernia striolata Tree Skink
Emydura macquarii Murray River Turtle
Eulamprus quoyii Eastern Water Skink
Geocrinia victoriana Victorian Smooth Froglet
Chelonia mydas Green Sea Turtle
Hemidactylus frenatus Asian House Gecko
Hemiergis decresiensis Three-toed Skink
Intellagama lesueurii Eastern Water Dragon
Intellagama lesueurii howittii Gippsland Water Dragon
Lampropholis guichenoti Garden Skink
Land Mullet Bellatorias major
Lerista bouganvilli Bouganville’s Skink
Limnodynastes dumerilii Banjo Frog
Limnodynastes peronii Striped Marsh Frog
Limnodynastes tasmaniensis Spotted Marsh Frog
Liopholis modesta Eastern Ranges Rock Skink
Litoria aurea Green and Golden Bell Frog
Litoria caerulea Green Tree Frog
Litoria chloris Red-eyed Tree Frog
Litoria ewingii Southern Brown Tree Frog
Litoria fallax Eastern Dwarf Tree Frog
Litoria pearsoniana Cascade Tree Frog
Litoria peronii Peron’s Tree Frog
Litoria subglandulosa New England Tree Frog
Litoria verreauxii Whistling Tree Frog
Mixophyse fasciolatus Great Barred Frog
Morethia boulengeri Boulenger’s Skink
Neobatrachus sudelli Common Spade-foot Toad
Parasuta flagellum Little Whip Snake
Pogona barbata Eastern Bearded Dragon
Pseudechis porphyriacus Red-bellied Black Snake
Pseudomoia pagenstecheri Tussock Skink
Pseudonaja textilis Common Brown Snake
Strophurus intermedius Eastern Spiny-tailed Gecko
Tiliqua scincoides Eastern Blue-tongue
Tropidechis carinatus Rough-scaled Snake
Uperoleia rugosa Rugose Toadlet



Cascade Tree Frog (Litoria pearsoniana), Springbrook QLD


Eastern Brown Snake (Pseudonaja textilis), Redesdale VIC


Gippsland Water Dragon (Intellagama lesueurii howittii), Mallacoota VIC


Scrub Python (Morelia kinghorni), Tully QLD


Red-eyed Tree Frog (Litoria chloris), Mt Warning NSW


Lesueur’s Velvet Gecko (Amalosia lesueurii), Retreat NSW

New paper – After the epidemic: ongoing declines, stabilisations and recoveries in chytridiomycosis impacted amphibians

csiro_scienceimage_1392_scanning_electron_micrograph_of_chytrid_fungusWe 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.

Latest paper: Manipulating wetland hydroperiod to improve occupancy rates by an endangered amphibian

IMG_1047_tweakedWorking on wetland biodiversity takes one to some rather odd places. In my case, it has meant copious hours at the back of industrial estates, in flooded quarry pits and dodging unsavory types around urban backwaters. Hardly Kakadu or the Okavango Delta. But even my haunts are glamorous compared to some. Take the Western Treatment Plant – 11,000 ha of sewage treatment ponds in Melbourne’s south-west that processes half of cities’ effluent (a daily contribution from ~2 million people). I can assure that the WTP looks and smells just like you imagine; hardly the sought of place that should fire the imagination of wetland ecologists.

And yet it does, because the WTP is wetland of global significance. It even sports a RAMSAR listing to prove it. Twitchers are particularly smitten with the place, flocking on mass to see Brolgas, Bitterns, Red-necked Avocets, Freckled Ducks, Pink-eared Ducks and even the critically-endangered Orange-bellied Parrot. For herpetologists like me, the attraction is frogs. As well as being home to squillions of Melbourne’s more common frogs, the WTP supports arguably the single largest remnant population of Growling Grass Frogs in the country.

Our latest paper focuses on keeping the resident Growler population booming. A collaboration with Andrew Hamer of the Australian Research Centre for Urban Ecology, Ecology Australia P/L and Will Steele of Melbourne Water, the paper uses monitoring data collected by EA over four seasons to update an existing model of the metapopulation dynamics of Growlers in Melbourne, and uses this model to predict how managing the hydroperiod of key wetlands could bolster occupancy rates. Furthermore, it includes a test of this management action in the field, assessing the change in occupancy rate at ponds that received top-up watering in the final year of the study. Encouragingly, occupancy rate increased among these ponds relative to those that didn’t receive top-up watering, suggesting that managing hydroperiod could increase both the range and abundance of Growlers at the WTP.

I’ll sign off here and let you peruse the paper for the juicy details (fire me an email if you can’t get through the paywall). If you’re interested in frogs, wetlands, management experiments, simulations or Bayesian statistics, you should like this one.

Here’s cheers to Parasite Ecology

IMG_1014_tweakedJust before Easter, my old friend Michael Scroggie alerted me to the fact that the good folks over at Parasite Ecology had posted a summary of our Ecology Letters paper on the role of chytridiomycosis in frog metapopulation dynamics. They really nailed the key messages of the paper, and even included a cheeky little cartoon that links our messages around migration to contemporary US politics. Nice!

Three new papers

A quick post to plug three papers that have hit the streets over recent months. The first is a case study of interspecific variation in the phenology of advertisement in frog communities. It was a fun paper to do, drawing together my own monitoring data from across northern Melbourne and coupling it with an extensive dataset collected by Stefano Canessa and Kirsten Parris across the same region in 2009. We built models of calling seasonality and within-season meteorological drivers for the resident frogs, and used these models to assess interspecific variation in peak calling periods. The paper is now published online over at Ecology and Evolution.

The second paper is the culmination of copious hard-work by Claire Keely, whose PhD I co-supervise. After 6 months trudging through the swamps of outer Melbourne searching for Growling Grass Frogs, followed by long hours in the lab genotyping hundreds of individuals, Claire has gained important data on the genetic structure and diversity of this endangered species around the city. It is great to see this work come to fruition. You can find out more about the paper and Claire’s PhD here. The paper itself is freely downloadable from Royal Society Open Science.

Third on the list is the first paper from Lucy Rose’s PhD. Lucy is interested in conservation decision making for freshwater systems in southern Australia, and has used our beloved Growler as a case study for integrating uncertainty in cost-effectiveness analyses. Lucy tackled the rather complex case of how Growlers will respond to urban growth in the Lockerbie Precinct north of Melbourne, working her way through the myriad of conservation options for the species to identify those that not only maximize cost-effectiveness, but minimize uncertainty due to demographic stochasticity and model imprecision. Lucy’s paper is currently online early at Conservation Biology.