Through The Sandglass

It's not just Namibian fairies

 

Described as one of the last great enigmas or mysteries, the so-called fairy circles of the arid lands of Namibia remain to be explained. Theories abound, and the fairies have stimulated "lively" academic debate, if not discord. The circles occur in their millions in a band of dry grassland stretching 1800 kilometres south from the Angolan border - but it's now clear that Australia has its own fairies.

In both places, countless circles dot the landscape like a pox of some kind:

Fairy circles in the Marienfluss Valley of Namibia.

(Google Earth image, ~ 650m across)

The circles are rimmed with (more or less) growing grass, vary in size up to several metres across and would seem to grow. Within them their is nothing but bare earth. Explanations include ostriches, rolling zebras, underground gas (or dragons' breath), footsteps of the gods, microbial activity, poisonous plants, termites, and the competition for scarce water. It's the last two that form the main rival hypotheses. As far as biologist Norbert Juergens of the University of Hamburg is concerned, it's termites. But Stephan Getzin of the Helmholtz Centre for Environmental Research (UFZ) in Leipzig disagrees - for him and his colleagues, fairy circles result from the way plants organize themselves in response to water shortage. Here's the abstract of this group's paper:

Vegetation gap patterns in arid grasslands, such as the “fairy circles” of Namibia, are one of nature’s greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomass–water feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil–water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass–water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.

 Note "no correlation with termite activity."

The patterns are fascinatingly regular and there has been a suggestion that the geometry of organisation is, bizarrely, directly equivalent to that of skin cells. Robert Sinclair, who heads the Mathematical Biology Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) in Japan, and his collaborator, Haozhe Zhang, were the first to identify this strange analogy. 

Two apparently unrelated systems on vastly different scales -- fairy circles in the Namibian desert (left) and microscopic skin cells (right) -- appear to share a similar pattern, which is very, very unusual.

Credit: Image courtesy of Okinawa Institute of Science and Technology - OIST

 

From the Science Daily report:

Both the majority of fairy circles and majority of cells have six neighbors. But the similarity gets even more specific -- the percentage of fairy circles with four, five, six, seven, eight and nine neighbors is essentially the same as the skin cells. "I didn't expect it to be so close," Sinclair said. "We spent a lot of time checking because it really looked too close to believe."

... The researchers suspect the patterns might be similar because both skin cells and fairy circles are fighting for space. If true, scientists might one day be able to glean information about systems just by analyzing patterns. For example, they could search for signs of life on other planets or moons, where images are usually the only data initially available.

Finding such a pattern could also benefit ecology and biology in general. Understanding processes on one scale could illuminate what is happening at the other end of the spectrum. "Otherwise, we need a whole new theory for each type of system we study, and may miss general principles, or, as some say, not see the forest for the trees," Sinclair said.

Self-organising systems and patterns are widespread and intriguing - I can't help but think of so-called "patterned ground," the permafrost polygons of the periglacial regions, the patterns on Mars (and now on Pluto), and various strange behaviours of granular materials...

Oh, and in aid of conservation in the NamibRand Nature Reserve, you can, if you wish, adopt a fairy circle. 

[Image at the head of this post credit, Stephan Getzin. The BBC has a very good piece summarising this mysterious phenomenon]

Sunbathing in the microscopic desert jungle

The desert has its own palette, distinctive and at the same time subtle yet dramatic. There are many factors at work creating the patterns and hues of arid lands - obviously the kind of sand, the kind of rock, the vegetation, minerals and salts, desert varnish - but there are also artists at work that we can't see and barely understand: microbial communities.

We can see the mosses and the lichens, but the vast ecosystem of bacteria and fungi operates essentially invisibly; we are only beginning to scratch the surface of the desert to reveal the ubiquity and importance of microbial life in environments we often describe as "lifeless." These are communities labelled "cryptic" by biologists, a useful term disguising the fact that they are something we really don't understand very well. I found this definition helpful, from a piece in Nature a few years ago titled "Body doubles" by Alberto G. Sáez and Encarnación Lozano:

Have you ever approached someone whom you thought you knew, talked to him with familiarity, only to find out later that he was a complete stranger, albeit remarkably similar in appearance to the person you had in mind, such as a twin brother? Well, taxonomists are similarly puzzled when they come across two or more groups of organisms that are morphologically indistinguishable from each other, yet found to belong to different evolutionary lineages. That is, when they discover a set of cryptic species.

The microscopic cryptic communities of arid lands form the well-known "desert" or "cryptobiotic" crusts that we now realise play key roles in the ecosystem, cycling carbon dioxide and nitrogen, providing resources for plant life, controlling drainage and the hydrologic behaviour of the soil, and reducing erosion - and hence, atmospheric dust. 

Among the leading researchers shedding light on these cryptic communities is Ferran Garcia-Pichel at Arizona State University's School of Life Sciences. For example, in 2013, togather with international colleagues, he published a paper titled "Temperature Drives the Continental-Scale Distribution of Key Microbes in Topsoil Communities." Science summarises the work as follows:

Soil microorganisms make up a substantial fraction of global biomass, turning over carbon and other key nutrients on a massive scale. Although the soil protects them somewhat from daily temperature fluxes, the distribution of these communities will likely respond to gradual climate change. ... [We] surveyed bacterial diversity across a range of North American desert soils, or biocrusts—ecosystems in which photosynthetic bacteria determine soil fertility and control physical soil properties such as erodability and water retention. Most of the sites were dominated by one of two cyanobacterial species, but their relative proportions were controlled largely by factors related to temperature. Laboratory enrichment cultures of the two species at different temperatures also showed temperature as a primary determining factor of bacterial diversity. It is unknown if temperature will affect the distribution of other soil microorganisms, but the marked shifts of these two keystone bacterial species suggest further change is in store for these delicate ecosystems.

The work, only available behind the Science paywall, was helpfully reported by Live Science. The two dominant "keystone" bacterial species are  Microcoleus vaginatus and M. steenstrupii, the former preferring cooler conditions whereas the latter likes things hot. As temperatures vary, things become competitive and warming conditions result in the mysterious steenstrupii taking over. Now, because these communities are microscopic and cryptic, we can only measure such effects - and detect which organisms are in the soil - through sophisticated DNA analysis. It is further results of this kind of painstaking and careful work that Garcia-Pichel and his colleagues have just published in Nature. With Estelle Couradeau, also at Arizona State, as the lead author, the paper describes - startlingly - how "Bacteria increase arid-land soil surface temperature through the production of sunscreens." Microcoleus vaginatus and M. steenstrupii are far from alone, and, amongst their companions are tribes of cyanobacteria such as the hundreds of species belonging to the genera Scytonema and Tolypothrix. These little critters dislike the sun and apply a biosynthetic sunscreen, scytonemin, an alkaloid pigment that strongly absorbs solar radiation and dissipates this energy as heat. This sunscreen can be seen as patches of darker colour covering areas of desert crust, as in this photo by Garcia-Pichel from the recent report on Science Daily.

This pigmentation may protect some members of the bacterial community, but it can locally warm up the surface by as much as 10 degrees C (18 degrees F). This has a dramatic effect on the health of the cool-loving Microcoleus vaginatus, but is welcomed by M. steenstrupii, who come to dominate as the sunscreen develops, at the expense of vaginatus. As Garcia-Pichel comments:

... we can show that the darkening of the crust brings about important modifications in the soil microbiome, the community of microorganisms in the soil, allowing warm-loving types to do better. This warming effect is likely to speed up soil chemical and biological reactions, and can make a big difference between being frozen or not when it gets cold... On the other hand, it may put local organisms at increased risk when it is already quite hot.

And this has to be happening on a global scale. As Estelle Coradeau suggests, "Because globally they cover some 20 percent of Earth's continents, biocrusts, their microbes and sunscreens must be important players in global heat budgets. We estimate that there must be some 15 million metric tons of this one microbial sunscreen compound...warming desert soils worldwide."

But because we have only a poor understanding of what exactly these desert crusts are and how they work, their roles in local ecology and global systems are impossible to define. It is only through the meticulous work of Ferran Garcia-Pichel and his team, together with others such as Jayne Belnap of the USGS in Moab, Utah, that we can begin to unravel the extraordinary nature and contributions of these long-ignored microbial desert communities. As Belnap has commented:

These are the only game in town to prevent dust storms and erosion, so they're really, really critical parts of this ecosystem. Yet we've never asked the question, 'who's really in there, and what's going to happen there as things shift?'

and, as reported in a piece on Belnap in High Country News, the palette and patterns of our arid lands owe much to an invisible living world: 

She also remains convinced that the dark shadows on the desert are the true — and fragile — foundation of the Colorado Plateau. "Whenever we pull on the thread of what makes the system tick," she says, "we end up with soil crusts on the other end."

[See also Belnap's USGS site at www.soilcrust.org. Crust photos credit: Linda and Dr. Dick Buscher, Live  Science "The Mysterious World of Cryptobiotic Soil."]

 

 

Behold, Cataglyphis bombycina is an hairy ant

In writing The Desert book, I became acutely aware that, as a humble geologist, my knowledge has profound limitations. I am not a biologist, botanist, ecologist  - the “ist” list of deficiencies goes on. However, in needing to try to describe the extraordinary (and often unappreciated) diversity of arid lands and the remarkable adaptations that permit it, I read – and learned – a great deal. I was fascinated to discover that, in terms of the olympics of heat-tolerance, the silver ant of the Sahara is the gold medal-winner – from Chapter 6:

In the Sahara, Cataglyphis bombycina, the silver ant and its cousin, Cataglyphis fortis, are the most heat-tolerant creatures known (except, of course, for some types of microbes).

To forage on the carcasses of the less strong, these ants wait in their nests, preparing heat shock proteins, until the heat of the day becomes intolerable for their predators, and then boldly go about their business with body temperatures up to 50 degrees centigrade and ground temperatures in the 60s. The proteins help protect them, as does their reflective silver colouring, and they move at an amazing speed (the human equivalent of over 400 kilometres per hour) on unusually long legs for an ant, keeping themselves off the searing ground surface. Their extraordinary navigational abilities guide them back to the nest by the shortest route. Even so, the silver ants can only spend twenty minutes outside before they succumb and become food for their colleagues.

 

And now the story of the silver ants’ clever adaptations and capabilities becomes even more extraordinary. Under the title “Staying Cool: Saharan Silver Ants”, the School of Engineering and Applied Science at Columbia University recently issued a press release (written by Holly Evarts) that I will reproduce here in its fascinating entirety:

Nanfang Yu, assistant professor of applied physics at Columbia Engineering, and colleagues from the University of Zürich and the University of Washington, have discovered two key strategies that enable Saharan silver ants to stay cool in one of the hottest terrestrial environments on Earth. Yu’s team is the first to demonstrate that the ants use a coat of uniquely shaped hairs to control electromagnetic waves over an extremely broad range from the solar spectrum (visible and near-infrared) to the thermal radiation spectrum (mid-infrared), and that different physical mechanisms are used in different spectral bands to realize the same biological function of reducing body temperature. Their research, “Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation,” is published June 18 in Science magazine.

“This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological task and ensure survival, in this case to prevent Saharan silver ants from getting overheated,” Yu says. “While there have been many studies of the physical optics of living systems in the ultraviolet and visible range of the spectrum, our understanding of the role of infrared light in their lives is much less advanced. Our study shows that light invisible to the human eye does not necessarily mean that it does not play a crucial role for living organisms.”

The project was initially triggered by wondering whether the ants’ conspicuous silvery coats were important in keeping them cool in blistering heat. Yu’s team found that the answer to this question was much broader once they realized the important role of infrared light. Their discovery that there is a biological solution to a thermoregulatory problem could lead to the development of novel flat optical components that exhibit optimal cooling properties.

“Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum,” Yu explains. “So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing.”

Saharan silver ants (Cataglyphis bombycina) forage in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging journeys, the ants search for corpses of insects and other arthropods that have succumbed to the thermally harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8” long) can survive under such thermally extreme and stressful conditions.

Using electron microscopy and ion beam milling, Yu’s group discovered that the ants are covered on the top and sides of their bodies with a coating of uniquely shaped hairs with triangular cross-sections that keep them cool in two ways. These hairs are highly reflective under the visible and near-infrared light, i.e., in the region of maximal solar radiation (the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface). The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum, where they serve as an antireflection layer that enhances the ants’ ability to offload excess heat via thermal radiation, which is emitted from the hot body of the ants to the cold sky. This passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.

“To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning,” says Yu. “Half of the energy loss at that moment is due to thermal radiation since your skin temperature is temporarily much higher than that of the surrounding environment.”

The researchers found that the enhanced reflectivity in the solar spectrum and enhanced thermal radiative efficiency have comparable contributions to reducing the body temperature of silver ants by 5 to 10 degrees compared to if the ants were without the hair cover. “The fact that these silver ants can manipulate electromagnetic waves over such a broad range of spectrum shows us just how complex the function of these seemingly simple biological organs of an insect can be,” observes Norman Nan Shi, lead author of the study and PhD student who works with Yu at Columbia Engineering.

Yu and Shi collaborated on the project with Rüdiger Wehner, professor at the Brain Research Institute, University of Zürich, Switzerland, and Gary Bernard, electrical engineering professor at the University of Washington, Seattle, who are renowned experts in the study of insect physiology and ecology. The Columbia Engineering team designed and conducted all experimental work, including optical and infrared microscopy and spectroscopy experiments, thermodynamic experiments, and computer simulation and modeling. They are currently working on adapting the engineering lessons learned from the study of Saharan silver ants to create flat optical components, or “metasurfaces,” that consist of a planar array of nanophotonic elements and provide designer optical and thermal radiative properties.

Yu and his team plan next to extend their research to other animals and organisms living in extreme environments, trying to learn the strategies these creatures have developed to cope with harsh environmental conditions.

“Animals have evolved diverse strategies to perceive and utilize electromagnetic waves: deep sea fish have eyes that enable them to maneuver and prey in dark waters, butterflies create colors from nanostructures in their wings, honey bees can see and respond to ultraviolet signals, and fireflies use flash communication systems,” Yu adds. “Organs evolved for perceiving or controlling electromagnetic waves often surpass analogous man-made devices in both sophistication and efficiency. Understanding and harnessing natural design concepts deepens our knowledge of complex biological systems and inspires ideas for creating novel technologies.”

The study was supported by the National Science Foundation under the Electronics, Photonics, and Magnetic Devices program (ECCS-1307948) and Physics of Living Systems program(PHY-1411445), and the Air Force Office of Scientific Research (AFOSR) Multidisciplinary Research Program of the University Research Initiative (MURI) program (FA9550-14-1-0389).

[Research was also carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory.]

And note that, once again, we are finding inspiration for new technologies not only from the life of the rainforest but from the desert.

 

[Header image: Bjørn Christian Tørrissen, courtesy of Creative Commons, Attribution-ShareAlike 3.0; other images via Columbia press release materials courtesy of Norman Nan Shi and Nanfang Yu] 

Excrementary, my dear Watson

Where does sand come from? A simple question, not always easily answered, and certainly not in some isolated tropical island environments. The Maldives Archipelago consists of 22 coral atolls, each containing a multitude of individual reefs, many of which surround a small island rimmed with glistening white sand. Those islands are vital, not only for the inhabitants and the economy, but for biodiversity and the health of the Maldives ecosystems. But they are vulnerable landforms, consisting simply of piles of unconsolidated sand, rarely more than 3m above sea level – and that sea level is rising. Understanding how the islands are maintained, the sources and movement of the sand that builds them, is an important, and, until now, poorly understood process. However, recent work by a team from the University of Exeter, in the UK, and collaborators from New Zealand and Australia, has revealed the details of reef island sustenance – and it all comes down to huge quantities of parrot fish excrement.

The study focused on the small island of Vakkaru (shown above), partly cultivated, partly vegetated, and completely surrounded by its white beaches, lagoon and reef. There is no source of sand other than that reef, for the Maldives are, after all, in the middle of the Indian Ocean and the nearest rivers flowing down to the shore, hills being weathered and eroded, are a very long way away. The whole sedimentary system is entirely biogenic, being run by the teeming ecosystem of the atolls. Exeter’s Chris Perry and his colleagues have meticulously quantified the major sediment-generating habitats, the abundance of different sediment-producing critters in each, and the rates of production. Vakkaru and its reef are little more than a maximum of a kilometre across, and the area of the island itself is less than 0.2 square kilometres, yet every year nearly 700 tons of new sediment is produced. Perhaps 10% of this comes from the broken-up calcareous segments that halimeda, a genus of macroalgae (or seaweed), produces as part of its structure, but more than 85% of the sand generated is comprised of parrotfish faeces.  

  

A variety of parrotfish, particularly the excavator species, Chlorurus sordidus and Chlorurus strongylocephalus, and the scraper species Scarus niger, Scarus frenatus, and Scarus rubroviolaceus, chew up coral in order to extract nutrition from algae, and then excrete the indigestible stuff – as sand-sized grains of calcium carbonate. And significant populations of parrotfish do so in prodigious quantities. It is reported that the native Hawaiian name for the female redlip parrotfish translates to “loose bowels,” and this video is a striking illustration:

 

All of this sediment manufacture takes place around the reef itself. Some sediment gets flushed out into the deeper ocean, but much is transported, particularly during the monsoon season, into and across the lagoon and up onto the island. During this process, many of the halimeda fragments are further broken up and the dominant sand of the island is parrotfish poop. This illustration from the paper published last month in Geology summarises how the system works: 

 

Many varieties of parrotfish are endangered, but it is clear that their role extends beyond key participants in biodiversity. As the report concludes:

While the need to protect parrotfish populations is commonly based on the need to sustain benthic ecological interactions, this study demonstrates their further critical beneficial role as producers of carbonate sediment and thus as key biogeoengineering species that can sustain local landform maintenance.

It has long been known that parrotfish manufacture sand – although rarely featured in tourism brochures, fish excrement is responsible for many of Hawaii’s gleaming white beaches – but this fascinating new analysis reveals the scale on which these bioengineers work.

 

[Parrotfish image by Chris Perry from the Science News and University of Exeter reports. Movie by Matthew Duncan. Paper: Linking reef ecology to island building: Parrotfish identified as major producers of island-building sediment in the Maldives, C.T. Perry, P.S. Kench, M.J. O'Leary, K.M. Morgan and F. Januchowski-Hartley, Geology, first published online April 27, 2015]

 

Georgia Tech Crab Lab: guest post on the art of sidewinding

Over the life of this blog, I have written a number of times on the remarkable and innovative work carried out at Georgia Tech’s Crab Lab, investigations into how critters get around in loose sand and how this can be applied to robotics (see, for example, here, here, and here). Crab Lab is headed up by Dan Goldman, and I was recently delighted (and flattered) that he contacted me about the “Sand” book. I asked if he and his colleagues would be willing to contribute a guest post – and here it is. Courtesy of Henry Astley, a postdoc “who loves all things snakes” and collaborator Joe Mendelson: the state of the art on the physics of sidewinding.

 

In spite of their barren reputation, deserts around the world teem with life, including a wide array of animals from beetles to camels. While much has been written about their adaptations to deal with two of the most notable characteristics of deserts, extreme temperatures and scarce water, far less attention has been paid to their interactions with the other distinguishing characteristic of many deserts: sand.

The ability to move from place to place is crucial for animals to find mates and resources, regulate their body processes, avoid predators, and colonize new environments. But sand makes locomotion difficult, whether moving on it or through it. Particularly problematic is that sand will behave as a solid under certain loads, but will yield and flow like a fluid under others, and very small differences in foot placement and movement can be the difference between moving and becoming hopelessly stuck. Animals deal with this challenging substrate in a variety of ways, whether by anatomical changes or selecting the best movement patterns.

Perhaps the strangest movement pattern of desert animals is the famous “sidewinding” locomotion, seen in certain snakes of sandy deserts around the world. While prominent herpetologist Clifford H. Pope wrote in 1955 “A study of [sidewinding] is recommended to anyone who likes to be confused,”, the underlying motion is quite clear when examined in detail. The snake lifts its head and moves it forward, placing it on the ground, then repeats this motion in a propagating wave down the body – see Science paper supplementary movies.

This produces a characteristic trackway consisting of a series of parallel lines, with the imprint of each scale on the belly clearly visible, showing that the snake does not slip (which would smear the tracks and erase the fine scale imprints). Ultimately, this seemingly complex motion can be reduced to a pair of waves producing vertical and horizontal body undulation, +- 90 degrees out of phase, which propagate together down the body. This simple model may be a “neuromechanical template”, a simple model of a motion which captures all the essential features, potentially serving a simple “target” for the animals to control their locomotion (see Sidewinding with minimal slip: Snake and robot ascent of sandy slopes). This two-wave template of sidewinding also produces sidewinding locomotion when applied to a snake robot, allowing the robot to move on sand effectively.

 

 Screen-grab from Science supplementary movies

This provides a great experimental tool, because the physics of sand have yet to be reduced to simple systems of equations (as has been the case in fluids for almost 200 years), making computer modeling of results difficult and time-consuming. However, the snake robot provides a “physical model” for movement in sand, allowing us to test hypothesized biological mechanisms. Further observations of biological snakes have revealed the modifications of the two-wave template responsible for effectively sidewinding up inclines and turning (see the recent PNAS paper), which in turn have further improved the effectiveness of the robot.

In spite of these insights, the serpents of the sand still hold many mysteries. Why do some snakes sidewind, while others don’t? Why can some species move effectively on sand, while others fail? How do sidewinders deal with obstacles? Can we reconstruct the evolution of this remarkable mode of locomotion from the tracks it has left, or has this history been lost in the sands of time? 

[My sincere thanks to all at Crab Lab for their work and this post. Photographs by Henry Astley]

Ecosystem engineers and keystone species

 

In large areas of Australia there are probably several hundred tons of termites in every square kilometre.

From The Desert, Lands of Lost Borders, Chapter 6:

The most ubiquitous (and irritating) vegetation in the Australian outback is spinifex, strictly Triodia. This coarse, tough grass grows in landscape-smothering tussocks, and its spiky leaf tips contain small shards of silica that have a habit of embedding themselves in the skin of passing animals, including humans.

Spinifex performs an important function in terms of dune stabilization and is a key participant in the fire ecology of the desert, but it is essentially inedible for animals and would smother the land and clog the ecosystem if left unchecked. In other climates, plant debris is cleared by wood-decaying fungi, but the desert is too dry for them. However, crucially, termites eat spinifex and there are a lot of them. Spinifex may be an archetypal feature of the landscapes of the outback, but so are termite mounds. They come in a bewildering array of shapes and sizes, each one extending far below the surface for water supply and providing a complex climate-controlled home to a community of hundreds of thousands of individuals. The termites consume the spinifex (along with a vast variety of other organic matter) and keep it under control, but they cannot digest it. For that, through a remarkable example of symbiosis, they require the specialized microbes in their gut that convert the cellulose to acetate, a kind of vinegar that then feeds the termites. Termite mounds provide safe havens for a variety of other creatures (some lizards lay their eggs in them) and the process of their construction moderates the desert soils, influencing water infiltration and evaporation, changing the structure and permeability. This, in turn, promotes plant growth and diversity, the entire vertebrate and invertebrate burrowing ecology and the food chain as a whole. Termite mounds in the Sahara and the Sahel are referred to as ‘houses of the devil’, but without this ‘keystone species’ arid lands would be very different — it has been estimated that most or all of the biomass produced in the Chihuahuan Desert is consumed by termites.

As a recent press release from Princeton University observed, “Termites might not top the list of humanity's favorite insects”, but it went on to highlight our on-going and emerging understanding of the critical role that they play in the arid ecosystems of the world’s arid lands:

new research suggests that their large dirt mounds are crucial to stopping the spread of deserts into semi-arid ecosystems and agricultural lands. The results not only suggest that termite mounds could make these areas more resilient to climate change than previously thought, but could also inspire a change in how scientists determine the possible effects of climate change on ecosystems.

In the parched grasslands and savannas, or drylands, of Africa, South America and Asia, termite mounds store nutrients and moisture, and — via internal tunnels — allow water to better penetrate the soil. As a result, vegetation flourishes on and near termite mounds in ecosystems that are otherwise highly vulnerable to "desertification," or the environment's collapse into desert.

Princeton University researchers report in the journal Science that termites slow the spread of deserts into drylands by providing a moist refuge for vegetation on and around their mounds. They report that drylands with termite mounds can survive on significantly less rain than those without termite mounds. The research was inspired by fungus-growing termites of the genus Odontotermes, but the theoretical results apply to all types of termites that increase resource availability on and/or around their nests.

This research is fascinating, but it would not be entirely surprising to farmers in the Sahel who are resurrecting – very successfully – the traditional methods of water management for new trees and for new crops. Digging a planting pit through the hardened surface and adding organic matter creates not only a water-conserving environment for plant growth, but attracts termites that process the organic material for use by the plants and aerate the soil through their tunnelling. And those tunnels are extraordinary. The internal structure of a termite mound (a complex ecosystem in its own right) has been dramatically demonstrated by the work of Scott Turner at The State University of New York College of Environmental Science and Forestry. Through taking plaster casts, he reveals the architectural skills of the ecosystem engineers as strange and compelling sculpture: 

 

The tunnelling continues far below the surface (termite mound materials that bring minerals from the subsurface have been used for gold prospecting in Australia) and for many metres beyond the mound. The scale of this landscape management activity is staggering: look carefully at this photo of just a small area of the Australian desert, and you will see hundreds of termite mounds. 

No, termites may not be our favourite insects, but our planet would be a different – and, arguably, worse – place without them.

 

[Image, “Crater termites of the worker and soldier castes attending to damage of their nest, Schanskop, Pretoria”, GNU Free Documentation License, Author JMK]

Fact-checking – and a new xerocole

Being still in the throes of editing and correcting the proofs for the new book (with the exception of compiling the index, the least enjoyable part of the whole process), I am particularly paranoid about fact-checking. I have one important (and, I'm sure, obvious) piece of advice: never believe anything you read or see in the press or on the web, without at least a triple-fact-check. 

I intend, in tandem with the new book, to evolve this blog naturally into looking at topics arid as well as arenaceous, and, as I have been doing for the last few years, I keep an eye on the news. I just came across a wonderful illustration of the fact that there remains an awful lot new under the sun still to be discovered – on every scale. As I emphasise in the book, while our awareness of the complexity, diversity and value of the ecosystems of arid lands is a long way behind that of temperate and tropical environments, we are, nevertheless, redressing that imbalance on a daily basis. Take, for example, the just-announced discovery of a new species of desert mammal, the weird and wonderful Macroscelides micus:

Scientists from the California Academy of Sciences have discovered a new species of round-eared sengi, or elephant-shrew, in the remote deserts of southwestern Africa. This is the third new species of sengi to be discovered in the wild in the past decade. It is also the smallest known member of the 19 sengis in the order Macroscelidea. The team’s discovery and description of the Etendeka round-eared sengi (Macroscelides micus) is published this week in the Journal of Mammalogy.

Sengis are otherwise known as elephant-shrews because they have a snout that resembles an elephant’s trunk, but they are not shrews – indeed, remarkably, they are more closely related to elephants. But the fact is that they are in a class of their own. Again from the California Academy of Sciences:

Few mammals have had a more colorful history of misunderstood ancestry than the elephant-shrews, or sengis. Most species were first described by Western scientists in the mid to late 19th century, when they were considered closely related to true shrews, hedgehogs, and moles in the order Insectivora. Since then, there has been an increasing realization that they are not closely related to any other group of living mammals, resulting in biologists mistakenly associating them with ungulates, primates, and rabbits. The recent use of molecular techniques to study evolutionary relationships, in addition to the more traditional morphological methods, has confirmed that elephant-shrews represent an ancient monophyletic African radiation. Most biologists currently include the elephant-shrews in a new supercohort, the Afrotheria, which encompasses several other distinctive African groups or clades. These include elephants, sea cows, and hyraxes (the Paenungulata); the aardvark and elephant-shrews, and the golden-moles and tenrecs.

The newly-discovered round-eared sengi is a charming little critter (image by John P. Dumbacher, the lead author of the paper):

Macroscelides micus is a true xerocole, an animal cleverly adapted to living – indeed, thriving – in arid conditions. This sengi lives on and around the Etendeka Plateau, a large area of volcanic rocks formed 130 million years ago as the South Atlantic was beginning to form – they were originally connected to the vast landscapes of the Paraná volcanics of Brazil.

This image from the California Academy of Sciences paper shows this stark and remote terrain (together with an example of the bizarre and unique xerophyte, welwitschia – but that’s another story):

Which brings me back to the beginning of this post and a slight rant about fact-checking. Like, I am sure, most of us, when a topic like this comes up, one of the first questions is where exactly is the Etendeka Plateau? Look at the two maps at the head of this post. On the left is the map reproduced in an article on the discovery in one of our illustrious British newspapers (and yes, given the recent news, I’m being sarcastic). Accompanied by the words “Mapped: Found in a remote area of Namibia, on the inland edge of the Namib Desert (mapped) at the base of the Etendeka Plateau”, it places the poor sengis right in the midst of the dunes of the Namib sand sea. Xerocoles they may be, but that’s pushing things a bit too far. The correct location – some 500 kms north – is shown on the right-hand map and is clearly illustrated in detail in the original paper if anyone had cared to check.

I find this time and time again. Google maps can’t even get my home location in London right, so why believe a map of an obscure and remote location reproduced in a newspaper? The answer is simply for no reason at all. It’s a sobering thought – if, on so many occasions, a simple fact-check on something you are particularly interested in reveals sloppiness and error, what about all the other stuff we don’t bother to fact-check?

More than fifty years ago, my parents particularly enjoyed the production that opened the newly constructed Mermaid Theatre in London (now sadly, and controversially, converted to a ‘Conference and Events Centre’). The play was a musical, based on an 18th century comedy by Henry Fielding, and included the satirical song It must be true. I remember, for years after, my father periodically singing to himself the opening line: “It must be true, for I read it in the papers, didn’t you?”

 Wise man, my Dad. 

Swimming in the sand

  

If you look at the two photos above, you will notice that the sand has moved – there is something down there…….

I have long been fascinated by the sandfish – the sand swimmer, the sand skink, or Scincus scincus – and wrote about this remarkable critter and its contribution to robotics a couple of times (see the link there for the earlier piece). But I never thought that I would actually see one and watch its performance.

However, during my recent visit to the Moroccan Sahara for a couple of days on the hump of a camel (more – perhaps – of that later), I was lucky. My guide and cameleer, Ibrahim, knew the desert like the back of his hand, every track and trail in the sand, every burrow, every bush, and, thank heavens, every route. We paused for a rest at a small oasis:

 

Ibrahim, grinning, comes up to me and opens his hand, in which, pert and unperturbed, was a sandfish, the poisson du sable.

 

After a little research on my return, I see that this is not Scincus scincus, the robotic inspiration, but probably its western cousin, Scincus albifasciatus laterimaculatus  - hardly important here, because both have the same amazing abilities. They do literally swim into and under the sand. It’s all beautifully fluid – the movement of the skink and the behaviour of the sand (click image to enlarge):

 

We re-excavated the poor little fellow several times and put him (or her – skink-sexing is not an area of my expertise) through his/her paces until the little critter became somewhat exhausted. A drink of water proved reviving, and off he/she disappeared into the sands.

 

As evidenced by the astonishing network of tracks and trails that greet you each morning in the sand, the majority of the local inhabitants are nocturnal. The sandfish is an exception, on the move during the day, and I am immensely grateful to Ibrahim and this delightful little skink for the pleasure of this meeting.  

Sunday sand food

 

Living in sand is not easy, and life – animal and vegetable - comes up with all kinds of wonderful solutions for doing so. Perhaps qualifying for one of the more bizarre adaptations is Pholisma sonorae, a perennial herb also known as sand food. It can be found in the sands of the Sonoran Desert, particularly in the Algodones Dunes. Sand food is unusual and bizarre in a number of ways: for a start, is a heterotoroph, lacking chlorphyll and looks for all the world like a dull grey powder-puff lying half-buried in the dunes sand. However, from April to June, it is covered in incongruously colourful flowers.

If the wind blows the sand away from around Pholisma sonorae, it takes on the appearance of a mushroom, with a long scaly stalk revealed. But this is only the beginning of the revelation – the stalk continues down as far as a couple of meters below the surface, eventually linking up with the roots of one of a number of different desert shrubs. For Pholisma sonorae is a parasite, depending for nutrients on the roots of its host. It does not, however, depend on its host for water – that it seems to deal with itself, absorbing water through stomata in its scale-like leaves; this independent skill means that sand food is not a parasite in the strict sense – its host does no appear to suffer from the attention of its guest.

And why sand food? The answer is simple: because Pholisma sonorae is remarkably clever at absorbing whatever water is available, its root is fleshy and edible, and it has long been a food source for the indigenous inhabitants of the Sonoran Desert.   

 

[Header image, Photo credit: USFWS/Jim A. Bartel, Creative Commons License; other images http://www.calflora.net/recentfieldtrips/algodonesdunes08.html; for more details and images of sand food, see, for example, http://waynesword.palomar.edu/pholisma.htm, CalPhotos, Berkeley, and DCREP, California’s Desert Renewable Energy Conservation Plan.]

A mystery resolved

So what is this? Land-art on the moon? An alien landing pad in the Utah desert? The work of nocturnal new-agers at the beach?

The answer of course, is none of these - in reality more fascinating and bizarre. To find out, go to the "art and visual ingenuity site," Colossal, and Spoon & Tomago