Latest paper: Dealing with trade-offs in destructive sampling designs for occupancy surveys

Destructive sampling. It’s a term that makes you squirm a little isn’t it? I feel the same when I think about certain marking techniques or the need to sacrifice specimens for Museum collections. Each presents a dilemma that most ecologists will confront at some point in their careers: the need to do something that is immediately at odds with our core values in pursuit of the greater good for species conservation.

In our latest paper* we tackle the dilemma posed by destructive sampling using a decision-theoretic approach. To be clear, the dilemma here is that some species are very difficult to detect by any other means than pulling apart their favored microhabitats. Hence, gaining the information we need to manage these species is nigh on impossible without some impact on their habitat. We can’t find out how widely they are distributed, we can’t establish the range of habitats on which they rely, and we can’t quantify how they are responding to the management we apply. The focal species of our paper is an excellent example. The Earless Skink (Hemiergis millewae) is an obligate denizen of Spinifex hummocks in the Mallee regions of southern Australia. In Victoria the species is listed as critically endangered, and there is real concern that fuel reduction burning poses a threat to remnant populations. Yet we also don’t know where all the remnant populations are, let alone how persistence relates to fire regimes. To gain that information requires surveys across the Victorian Mallee, but the only practical way of doing those surveys is to prize apart the Spinifex hummocks on which the species relies.

Stefano Canessa took up the challenge of designing surveys for Hemiergis, using a hard-earned survey dataset acquired by Peter Robertson and Ian Sluiter at select sites in the Murray-Sunset National Park. The approach Stef devised finds the number of Spinifex hummocks a surveyor must sample at a site to ensure a threshold detection probability is reached (0.9, 0.95 etc), using a weighting system to reflect a surveyors choice between minimizing the number of hummocks searched and minimizing the quality of hummocks searched. This last bit is important, because Hemiergis don’t use hummocks at random; they like the big ones. So a surveyor can reduce the number of hummocks searched at a site by targeting the biggest ones available, because detection probabilities are higher on a per hummock basis for the bigger ones. But of course this removes the best microhabitats for the species. Instead, a surveyor can target small or medium-sized hummocks and leave the big ones, but this requires removing more hummocks to achieve the desired probability of detection and perhaps leads to greater impacts in the long run (because big hummocks senesce and need to be replaced by adolescent hummocks).

It’s a tricky problem, but Stef’s technique makes the trade-offs and choices clear, and enables repeatable and transparent decisions to be made (as decision theory is intended to do). Stef even provides an Excel worksheet to run the decision analysis, making the approach immediately accessible to managers. But the technique also has wider appeal. Destructive sampling is used to survey a range of species, and the fundamentals of Stef’s approach apply in each case, because all involve a central trade-off between maximizing detection probabilities and minimizing impacts on the focal species’ habitat.

*This link will take you to a post-print version of the paper, rather than the published version, because PLOS completely mangled our figures and refuse to fix them. The published version can be found here.

The Wonders of Convergence

One of the most captivating things about evolution is its propensity to produce identical twins on opposite sides of the globe. Species that are near inseparable morphologically, ecologically and behaviorally, but which have very different DNA. They don’t have common forebears, at least not recent ones. Instead, having been buffeted by equivalent forces over the millennia, and run a parallel race of natural selection, they’ve reached the same evolutionary sweet spot. They’ve been sculpted by the same chisel and converged.

The wonders of convergence were bought home to me again this week while working on a paper I’ve been meaning to write for some time. It concerns the phenology of mate-calling among frogs from my home town of Melbourne, in southern Australia (‘phenology’ being the timing and determinants of periodic biological events). In my ramblings through the literature, I came across a great paper by Daniel Saenz and colleagues on the phenology of mate-calling in a community of frogs from eastern Texas. Texas, that’s roughly 14,000 km from Melbourne, on the other side of the world’s greatest ocean. And yet, what Saenz et al. had to say about the frogs they studied sounded very familiar. Oddly familiar.

And so, with Google’s help, I set to work looking up these Texan amphibians. Surprise, surprise, they are the same frogs I work on 14,000 km away. Quite unrelated phylogenetically, but counterparts nonetheless. Take a look for yourself. In the following pairs of photos, the Australian species is on the left and its Texan analogue on the right. It’s incredible, isn’t it?

Whistling Tree Frog, Litoria verreauxii

Whistling Tree Frog, Litoria verreauxii

Western Chorus Frog, Pseudacris triseriata

Western Chorus Frog, Pseudacris triseriata

 

 

 

 

 

 

Growling Grass Frog, Litoria raniformis

Growling Grass Frog, Litoria raniformis

Common Bullfrog, Rana catesbeiana

Common Bullfrog, Lithobates catesbeiana

 

 

 

 

 

 

 

Common Froglet, Crinia signifera

Common Froglet, Crinia signifera

Northern Cricket Frog, Acris crepitans

Northern Cricket Frog, Acris crepitans

 

 

 

 

 

 

Peron's Tree Frog, Litoria peronii

Peron’s Tree Frog, Litoria peronii

Gray Tree Frog, Hyla versicolor

Gray Tree Frog, Hyla versicolor

 

 

 

 

 

 

Sudell's Frog, Neobatrachus sudelii

Sudell’s Frog, Neobatrachus sudelii

Eastern Spadefoot Toad, Scaphiopus holbrookii

Eastern Spadefoot Toad, Scaphiopus holbrookii

 

 

 

 

 

 

Spotted Marsh Frog, Limnodynastes tasmaniensis

Spotted Marsh Frog, Limnodynastes tasmaniensis

Southern Leopard Frog, Rana sphenocephala

Southern Leopard Frog, Lithobates sphenocephala

 

 

 

 

 

 

 

Photo sources (those not listed are my own):

Western Chorus Frog –  calphotos.berkeley.edu, photographer Todd Pierson.
Common Bullfrog – http://www.discoverlife.org/, photographer unknown.
Northern Cricket Frog – https://www.flickr.com/photos/52463647@N08/, photographer Melville Osborne.
Gray Tree Frog – http://www.californiaherps.com/noncal/misc/miscfrogs/pages/h.versicolor.html, photographer Gary Nafis.
Sudell’s Frog – www.stewartmacdonald.com.au, photographer Stuart MacDonald.
Eastern Spadefoot Toad – http://www.discoverlife.org/, photographer Todd Pierson
Spotted Marsh Frog – http://bwvp.ecolinc.vic.edu.au/fieldguide/fauna/spotted-marsh-frog, photographer Craig Cleeland
Southern Leopard Frog – http://www.frogforum.net/, photographer John Clare

Conservation photos, Part VIII: Skinks

Skinks. Australia is crawling with them, figuratively and literally. At last count we had 339 species. 339 species! And yet the richness of species is only half the story. Australia has a skink for every occasion. Giant skinks and miniature skinks. Skinks that live half of their lives in the alpine deep freeze, and others that toil through the harshest desert heat. Skinks that scale trees in a blistering flash, and others that have lost all but the last vestige of their limbs. Skinks whose days are spent cavorting in tight-knit family units, and others who are murderously territorial. Skinks saturated with colour, and skinks whose camouflage is near impregnable. Skinks whose range extends over hundreds of square kilometers, and others that persist nowhere else but a speck of granite in the Southern Ocean. You would be hard pressed to find a more diverse radiation than the Australian Scincidae…

Eastern Robust Slider, Lerista punctatovittata. Big Desert, Victoria

Eastern Robust Slider, Lerista punctatovittata. Big Desert, Victoria

South-west Crevice Skink, Egernia napoleonis. Albany, Western Australia

South-west Crevice Skink, Egernia napoleonis. Poorongorup NP, Western Australia

Boulenger's Skink, Morethia boulengeri. Mansfield, Victoria

Boulenger’s Skink, Morethia boulengeri. Mansfield, Victoria

White's Skink, Liopholis whitii, Grampians National Park, Victoria

White’s Skink, Liopholis whitii. Grampians NP, Victoria

Ctenotus brachyonyx, Ouyen, Victoria

Ctenotus brachyonyx. Ouyen, Victoria

Tussock Skink, Pseudemoia pagenstecheri. Craigieburn, Victoria

Tussock Skink, Pseudemoia pagenstecheri. Craigieburn, Victoria

Ragged Snake-eyed Skink, Cryptoblepharus pannosus. Murray-Sunset NP, Victoria

Ragged Snake-eyed Skink, Cryptoblepharus pannosus. Murray-Sunset NP, Victoria

Southern Grass Skink, Pseudemoia entrecasteauxii. Mt Baw Baw NP, Victoria

Southern Grass Skink, Pseudemoia entrecasteauxii. Mt Baw Baw NP, Victoria

Conservation photos VII. Weird and wonderful

Evolution crafts some wacky creatures. Birds that can’t fly. Squirrels that can. Mammals that lay eggs. Worms that luminesce. Vampire bats. Goblin fish. Octopus. I must admit that I have a considerable soft spot for these ecological and evolutionary oddities. They are just so fascinating; so mind-bogglingly weird. So indulge me as a list a few more. A few that I’ve had the great joy of seeing in the flesh, and whom I dearly hope to see again. Frogs whose finely textured and brilliantly patterned skin has inspired Aboriginal art for millennia. Dragons that spend their days munching hundreds of tiny, acrid ants, and whose skin not only wards off predators with a litany of devilish thorns, but also pumps water directly to their mouth by capillary action. Miniaturised snakes whose diet is restricted entirely to lizard eggs (that rarest of commodities) and others whose tail so perfectly mimics a grub – in both form and function – that it brings dinner right to their door. Lizards who swim through sand, having long ago cast aside the limbs that hinder their progress. And snakes whose morphology just takes your breath away. Whose beauty you can barely fathom, and whose existence re-affirms why you took up the cause in the first place….

Holy Cross Frog, Notaden bennetti

Holy Cross Frog, Notaden bennetti

Thorny Devil, Moloch horridus

Thorny Devil, Moloch horridus

 

 

 

 

 

 

 

 

 

Black-naped Snake, Neelaps bimaculatus

Black-naped Snake, Neelaps bimaculatus

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Common Death Adder, Acanthophis antarticus

Common Death Adder, Acanthophis antarcticus

 

 

 

 

 

 

 

 

Red-tailed Worm Lizard, Aprasia inaurita

Red-tailed Worm Lizard, Aprasia inaurita

 

 

 

 

 

 

 

 

 

Bandy Bandy, Vermicella vermicella

Bandy Bandy, Vermicella annulata

 

Conservation Photos Part VI: Mountain Herps

Australia is not renowned for its mountains. Our medal tally at the last Winter Olympics will tell you that. And yet we have a mountain range that challenges the grandest the world has to offer. Not in height, no. But for scale, diversity and sheer spectacle? You have to give me that. The range I’m talking about is of course the Great Dividing Range – a conglomerate of mountains that stretches 3500 km along Australia’s eastern seaboard. Like most Australians, I’ve only nibbled at the edges of the Great Divide. But what a rewarding taste it has been. I’ve rambled through environments ranging from alpine meadows to sub-tropical rainforests, and had the pleasure of crossing paths with herps ranging from the tiniest of skinks, to dragons, elapids, frogs and pythons…

Alpine Copperhead, Austrelaps ramsayi. Mt Baw Baw, Victoria

Alpine Copperhead, Austrelaps ramsayi. Mt Baw Baw, Victoria

Maccoy's skink, Nannoscincus maccoyi.

Maccoy’s skink, Nannoscincus maccoyi. Mansfield, Victoria

Common Froglet, Crinia signifera. Grampians National Park, Victoria

Common Froglet, Crinia signifera. Grampians National Park, Victoria

White Lipped Snake, Drysdalia coronoides. Mt Baw Baw, Victoria

White Lipped Snake, Drysdalia coronoides. Mt Baw Baw, Victoria

Spencer's skink, Pseudomoia spenceri. Mt Baw Baw, Victoria

Spencer’s Skink, Pseudemoia spenceri. Mt Baw Baw, Victoria

Mountain Dragon, Rankinia diemensis. Grampians National Park, Victoria

Mountain Dragon, Rankinia diemensis. Grampians National Park, Victoria

Eastern Ranges Rock-skink, Liopholis modesta

Eastern Ranges Rock-skink, Liopholis modesta. New England Tableland, NSW

Carpet Python, Morelia spilota mcdowelli. Sunshine Coast hinterland, Queensland

Carpet Python, Morelia spilota mcdowelli. Sunshine Coast hinterland, Queensland

Conservation Photos Part V: Landscapes II

Because, well, why not?

coast

The stunning coast of Albany, Western Australia

 

 

 

 

 

 

 

 

 

Desert blooms on a Lindsay Island sand dune, Victoria

Desert blooms on a Lindsay Island sand dune, Victoria

 

 

 

 

 

 

 

 

 

Native Pine (Callistris) battling out on a granite scree, Girraween National Park, Queensland

Native Pine battle it out on a granite scree, Girraween NP, Queensland

 

 

 

 

 

 

 

 

 

Ominous skies over south-western Western Australia

Ominous skies over south-western Western Australia

 

 

 

 

 

 

 

 

 

Blue bush, Myall and Whyalla sandstone, South Australia

Blue bush, Myall and sandstone, Whyalla, South Australia

 

 

 

 

 

 

 

 

 

Water lillies (Potamogeton) in a desert oasis, Murray-Sunset NP, Victoria

Water lillies in a desert oasis, Murray-Sunset NP, Victoria

 

 

 

 

 

 

 

 

 

Morning light on granite, Wilson Promontory NP, Victoria

Morning light on granite, Wilsons Promontory NP, Victoria

 

 

 

 

 

 

 

 

 

Limestone as far as the eye can see, Eyre Peninsula, South Australia

Limestone as far as the eye can see, Eyre Peninsula, South Australia

 

 

 

 

 

 

 

 

 

The sun dips below the western horizon, Mandurah, Western Australia

The sun dips below the western horizon, Mandurah, Western Australia

 

Conservation Photos Part IV: Landscapes

If I had to sum up my research in one word it would be autecology. I’m fascinated by the stories of individual species. Their life-histories, their patterns of activity and dispersal, their diets, their habitat requirements. In short, the axes that influence the survival of individuals and populations. But it’s just my particular window on ecosystem function. It’s a form of abstraction. Like all applied ecologists, I’m ultimately concerned with the persistence of entire ecosystems. So how does an autecologist indulge their passion for ecosystems directly? Through landscape photography, of course!

Morning light on the grassy woddlands of Lake Tutchewop, Victoria

Morning light on the open woodlands of Lake Tutchewop, Victoria

Sub-tropical rainforest of the Nightcap Range, NSW

The clear waters of a sub-tropical rainforest stream in the Nightcap Range, NSW

Waning moon over the Red Gum woodlands of southern New South Wales

Waxing moon over the Red Gum woodlands of southern New South Wales

Limestone bluffs of south-western Western Australia

Limestone heaths of south-western Western Australia

 

Granite scree of Mt Hope, Victoria

The granite heathlands of Mt Hope, Victoria

Cascade of a Mt Baw Baw rivulet

Light dancing on a Mt Baw Baw rivulet

Sandstone escarpment of Table Mountain, with the Murray Valley below

Sandstone escarpment of Table Mountain, with the Murray floodplain below

 

Storm brewing over an Alpine meadow

Storm brewing on an Alpine meadow

Deep summer in central Victoria

Deep summer amongst the granite inselbergs of central Victoria

Sunset on the Brunswick River estuary

Sunset on the Brunswick River estuary

Conservation Photos Part III: Melbourne’s Volcanic Plains

I couldn’t tell you how many hours I’ve spent wandering Melbourne’s volcanic plains. I grew up a just stones throw from them, on the sedimentary hills east of the Plenty River. Perhaps it is sacrilegious to say, but the volcanic plains were far more interesting for a boy obsessed with herpetology. Whereas the Red Box woodlands east of the river offered fleeting glimpses of the odd Garden Skink, the volcanic plains west of the river offered Little Whip Snakes, Brownsnakes, Tussock Skinks, Pobblebonks, Bluetongue Lizards, Cunningham Skinks, Copperheads, Tiger Snakes, Small-eyed Snakes. The choice was easy….

Eastern Water Skink, Eulamprus tympanum

Southern Water Skink, Eulamprus tympanum

Brown Tree Frog, Litoria ewingii

Brown Tree Frog, Litoria ewingii

Small-eyed Snake, Cryptophis nigrescens

Small-eyed Snake, Cryptophis nigrescens

Growling Grass Frog, Litoria raniformis

Growling Grass Frog, Litoria raniformis

Striped Skink, Ctenotus robustus

Striped Skink, Ctenotus robustus

Common Brownsnake, Pseudonaja textilis

Common Brownsnake, Pseudonaja textilis

Tussock Skink, Pseudemoia pagenstecheri

Tussock Skink, Pseudemoia pagenstecheri

Little Whip Snake, Parasuta flagellum

Little Whip Snake, Parasuta flagellum

Pobblebonk, Limnodynastes dumerilii

Pobblebonk, Limnodynastes dumerilii

A Natural High

P1000983Tell me this – have you ever taken drugs? Yes? No? The answer depends on one’s definition, but I’ll bet that many of you will admit to dabbling in some form of stimulant. We are, as a society, obsessed with them. Dark aromatic shots of plant extracts; delicate paper tubes delivering wafts of nicotine; colourful vessels of molten sand filled with fermented fruit juice; little polyethylene baggies carrying a fine dust of crystalline tropane alkaloids. We have employed all our ingenuity in search of a high.

Why? Let me give you my theory. I think our craving for stimulants is an attempt to the replace the pulses of endorphins that once accompanied our daily rambling in the wilds. I can honestly say that nature has given me by far the biggest highs of my life. I’ve stood at the edge of Mt Meg’s spectacular granite bluffs, with blood coursing and nostrils flaring, and believed that I could soar off if only I had the courage to jump. I’ve perched atop dunes of the Big Desert and felt my skin tingle with awe. I’ve stood waist deep in the Merri Creek with a full moon overhead and frogs calling all around, and been so fulfilled that if I’d slipped into the murky depths at that very instant, I would have died happy.

My most recent of these experiences was also the most profound. It was March 2011. La Niña had just prized southern Australia loose from El Niños’ grasp, bringing rain and plenty of it. The Murray-Darling catchment, wilting and gasping after ten years of drought, was reborn. Floods spread across every inch of the basin, coalescing at the junction of the Murray and Darling Rivers in Victoria’s north-west. With haste, my old friend Jeremy Tscharke and I packed the car and headed north to glimpse the spectacle. What we found eclipsed even our wildest dreams. 

Land that two years before was literally dying of thirst was now heaving with life. Supposedly long dead Red Gums re-sprouted in effervescent green. Wetlands that we presumed had seen their last flood years before now brimmed with fish and turtles. Frogs reclaimed the flood plain in such numbers that one had to be careful where they placed their feet. It was stunning, and a truly humbling experience.

The climax was a sunset that Jeremy and I will never forget. We’d headed up a flooded Lindsay River in search of ‘Big Red’ – a Red Gum of gargantuan proportions we’d seen previously on aerial imagery. We found her just as the sun dipped below the western horizon. The sky progressed through golden, to pink and eventually to deep violet. As we marveled at this great tree, we talked about the history it had seen. Big Red would already have been a towering giant when Captain Cook sailed up Australia’s eastern seaboard. She could well have sheltered families of Aboriginal people from inclement weather, and her hollow limbs must have once been home to regionally extinct marsupials. Undoubtedly, she has seen scores of floods of the scale of the 2011 epic. This tree was, quite simply, a living piece of history that we could touch and caress and imbibe. We had found our Totem, and returned to camp with a sense of bliss that no substance could ever hope to replicate.

Dwarfed by Big Red

Dwarfed by Big Red. A little shaky, but steady hands are hard to come by under this beauty. Photo: J. Tscharke

Sunset on the Lindsay River I. Photo: J. Tscharke

Bliss I. Photo: J. Tscharke

Sunset on the Lindsay River II. Photo: J. Tscharke

Bliss II. Photo: J. Tscharke

Sunset on the Lindsay River III. Photo: J. Tscharke

Bliss III. Photo: J. Tscharke