Oct 19, 2018
As further support for that notion, the researchers also found the victims: other fish that had apparently been nibbled on in the same limestone deposits in South Germany (the quarry of Ettling in the Solnhofen region) where this piranha-like fish was found.
"We have other fish from the same locality with chunks missing from their fins," says David Bellwood of James Cook University, Australia. "This is an amazing parallel with modern piranhas, which feed predominantly not on flesh but the fins of other fishes. It's a remarkably smart move as fins regrow, a neat renewable resource. Feed on a fish and it is dead; nibble its fins and you have food for the future."
The newly described fish is part of the world famous collections in the Jura-Museum in Eichstätt. It comes from the same limestone deposits that contained Archaeopteryx.
Careful study of the fossilized specimen's well-preserved jaws revealed long, pointed teeth on the exterior of the vomer, a bone forming the roof of the mouth, and at the front of both upper and lower jaws. Additionally, there are triangular teeth with serrated cutting edges on the prearticular bones that lie along the side of the lower jaw.
The tooth pattern and shape, jaw morphology, and mechanics suggest a mouth equipped to slice flesh or fins, the international team of researchers report. The evidence points to the possibility that the early piranha-like fish may have exploited aggressive mimicry in a striking parallel to the feeding patterns of modern piranha.
"We were stunned that this fish had piranha-like teeth," says Martina Kölbl-Ebert of Jura-Museum Eichstätt (JME-SNSB). "It comes from a group of fishes (the pycnodontids) that are famous for their crushing teeth. It is like finding a sheep with a snarl like a wolf. But what was even more remarkable is that it was from the Jurassic. Fish as we know them, bony fishes, just did not bite flesh of other fishes at that time. Sharks have been able to bite out chunks of flesh but throughout history bony fishes have either fed on invertebrates or largely swallowed their prey whole. Biting chunks of flesh or fins was something that came much later."
Or, so it had seemed.
"The new finding represents the earliest record of a bony fish that bit bits off other fishes, and what's more it was doing it in the sea," Bellwood says, noting that today's piranhas all live in freshwater. "So when dinosaurs were walking the earth and small dinosaurs were trying to fly with the pterosaurs, fish were swimming around their feet tearing the fins or flesh off each other."
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|California wine country with a trees nestled on the hillside.|
But few types of bats live on American farms. That's because the current practice of monoculture -- dedicating large swathes of land to a single crop -- doesn't give the bats many places to land or to nest.
Diversifying working lands -- including farmland, rangeland and forests -- may be key to preserving biodiversity in the face of climate change, says a new review paper published this week in Science by conservation biologists at the University of California, Berkeley.
Diversification could be as simple as adding trees or hedgerows along the edges of fields, giving animals like birds, bats and insects places to live, or as complex as incorporating a patchwork of fields, orchards, pasture and flowers into a single working farm.
These changes could extend the habitat of critters like bats, but also much larger creatures like bears, elk and other wildlife, outside the boundaries of parks and other protected areas, while creating more sustainable, and potentially more productive, working lands.
"Protected areas are extremely important, but we can't rely on those on their own to prevent the pending sixth mass extinction," said study co-author Adina Merenlender, a Cooperative Extension Specialist in the Department of Environmental Science, Policy and Management at UC Berkeley. "This is even more true in the face of climate change, because species will need to move around to adapt to shifts in temperature and climate."
Maintaining even small pieces of the original landscape -- even a single tree- can help conserve the original diversity of species, Merenlender said.
Clearing oak woodlands and shrublands to establish large vineyards hits many native species hard. Animals that are well adapted to urban and agricultural areas, such as mockingbirds, house finches and free-tail bats, continue to flourish, while animals that are more sensitive to disturbance, like acorn woodpeckers, orange-crowned warblers and big brown bats, begin to drop away.
"If you can leave shrubs, trees and flowering plants, the habitat suitability -- not just for sensitive birds but also for other vertebrates -- goes way up," Merenlender said. This is true not only in California's vineyards, but on working lands around the world.
Incorporating natural vegetation makes the farm more hospitable to more creatures, while reducing the use of environmentally degrading chemicals like herbicides, pesticides and human-made fertilizer.
The ideal farming landscape includes woodland pastures and vegetable plots bumping up against orchards and small fields, said Claire Kremen, a professor in the Department of Environmental Science, Policy and Management.
Integrating livestock produces manure which can fertilize the crops, while those same crops produce feed for livestock. Birds and bats provide pest control, and bees boost crop production by pollinating plants.
"It is possible for these working landscapes to support biodiversity but also be productive and profitable," Kremen said. "And ultimately, this is where we have to go. We just can't keep mining our soils for their fertility and polluting our streams -- in the end, this will diminish our capacity to continue producing the food that we need. Instead, we must pay attention to the species, from microbes to mammals, that supply us with critical services, like pollination, pest control and nutrient cycling"
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NASA's Hubble Space Telescope is observing such stars through a large program called HAZMAT -- Habitable Zones and M dwarf Activity across Time.
"M dwarf" is the astronomical term for a red dwarf star -- the smallest, most abundant and longest-lived type of star in our galaxy. The HAZMAT program is an ultraviolet survey of red dwarfs at three different ages: young, intermediate, and old.
Stellar flares from red dwarfs are particularly bright in ultraviolet wavelengths, compared with Sun-like stars. Hubble's ultraviolet sensitivity makes the telescope very valuable for observing these flares. The flares are believed to be powered by intense magnetic fields that get tangled by the roiling motions of the stellar atmosphere. When the tangling gets too intense, the fields break and reconnect, unleashing tremendous amounts of energy.
The team has found that the flares from the youngest red dwarfs they surveyed -- just about 40 million years old -- are 100 to 1,000 times more energetic than when the stars are older. This younger age is when terrestrial planets are forming around their stars.
Approximately three-quarters of the stars in our galaxy are red dwarfs. Most of the galaxy's "habitable-zone" planets -- planets orbiting their stars at a distance where temperatures are moderate enough for liquid water to exist on their surface -- likely orbit red dwarfs. In fact, the nearest star to our Sun, a red dwarf named Proxima Centauri, has an Earth-size planet in its habitable zone.
However, young red dwarfs are active stars, producing ultraviolet flares that blast out so much energy that they could influence atmospheric chemistry and possibly strip off the atmospheres of these fledgling planets.
"The goal of the HAZMAT program is to help understand the habitability of planets around low-mass stars," explained Arizona State University's Evgenya Shkolnik, the program's principal investigator. "These low-mass stars are critically important in understanding planetary atmospheres."
The results of the first part of this Hubble program are being published in The Astrophysical Journal. This study examines the flare frequency of 12 young red dwarfs. "Getting these data on the young stars has been especially important, because the difference in their flare activity is quite large as compared to older stars," said Arizona State University's Parke Loyd, the first author on this paper.
The observing program detected one of the most intense stellar flares ever observed in ultraviolet light. Dubbed the "Hazflare," this event was more energetic than the most powerful flare from our Sun ever recorded.
"With the Sun, we have a hundred years of good observations," Loyd said. "And in that time, we've seen one, maybe two, flares that have an energy approaching that of the Hazflare. In a little less than a day's worth of Hubble observations of these young stars, we caught the Hazflare, which means that we're looking at superflares happening every day or even a few times a day."
Could super-flares of such frequency and intensity bathe young planets in so much ultraviolet radiation that they forever doom chances of habitability? According to Loyd, "Flares like we observed have the capacity to strip away the atmosphere from a planet. But that doesn't necessarily mean doom and gloom for life on the planet. It just might be different life than we imagine. Or there might be other processes that could replenish the atmosphere of the planet. It's certainly a harsh environment, but I would hesitate to say that it is a sterile environment."
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|MIT neuroscientists can now record electrical activity from the dendrites of human neurons.|
Using hard-to-obtain samples of human brain tissue, MIT neuroscientists have now discovered that human dendrites have different electrical properties from those of other species. Their studies reveal that electrical signals weaken more as they flow along human dendrites, resulting in a higher degree of electrical compartmentalization, meaning that small sections of dendrites can behave independently from the rest of the neuron.
These differences may contribute to the enhanced computing power of the human brain, the researchers say.
"It's not just that humans are smart because we have more neurons and a larger cortex. From the bottom up, neurons behave differently," says Mark Harnett, the Fred and Carole Middleton Career Development Assistant Professor of Brain and Cognitive Sciences. "In human neurons, there is more electrical compartmentalization, and that allows these units to be a little bit more independent, potentially leading to increased computational capabilities of single neurons."
Harnett, who is also a member of MIT's McGovern Institute for Brain Research, and Sydney Cash, an assistant professor of neurology at Harvard Medical School and Massachusetts General Hospital, are the senior authors of the study, which appears in the Oct. 18 issue of Cell. The paper's lead author is Lou Beaulieu-Laroche, a graduate student in MIT's Department of Brain and Cognitive Sciences.
Dendrites can be thought of as analogous to transistors in a computer, performing simple operations using electrical signals. Dendrites receive input from many other neurons and carry those signals to the cell body. If stimulated enough, a neuron fires an action potential -- an electrical impulse that then stimulates other neurons. Large networks of these neurons communicate with each other to generate thoughts and behavior.
The structure of a single neuron often resembles a tree, with many branches bringing in information that arrives far from the cell body. Previous research has found that the strength of electrical signals arriving at the cell body depends, in part, on how far they travel along the dendrite to get there. As the signals propagate, they become weaker, so a signal that arrives far from the cell body has less of an impact than one that arrives near the cell body.
Dendrites in the cortex of the human brain are much longer than those in rats and most other species, because the human cortex has evolved to be much thicker than that of other species. In humans, the cortex makes up about 75 percent of the total brain volume, compared to about 30 percent in the rat brain.
Although the human cortex is two to three times thicker than that of rats, it maintains the same overall organization, consisting of six distinctive layers of neurons. Neurons from layer 5 have dendrites long enough to reach all the way to layer 1, meaning that human dendrites have had to elongate as the human brain has evolved, and electrical signals have to travel that much farther.
In the new study, the MIT team wanted to investigate how these length differences might affect dendrites' electrical properties. They were able to compare electrical activity in rat and human dendrites, using small pieces of brain tissue removed from epilepsy patients undergoing surgical removal of part of the temporal lobe. In order to reach the diseased part of the brain, surgeons also have to take out a small chunk of the anterior temporal lobe.
With the help of MGH collaborators Cash, Matthew Frosch, Ziv Williams, and Emad Eskandar, Harnett's lab was able to obtain samples of the anterior temporal lobe, each about the size of a fingernail.
Evidence suggests that the anterior temporal lobe is not affected by epilepsy, and the tissue appears normal when examined with neuropathological techniques, Harnett says. This part of the brain appears to be involved in a variety of functions, including language and visual processing, but is not critical to any one function; patients are able to function normally after it is removed.
Once the tissue was removed, the researchers placed it in a solution very similar to cerebrospinal fluid, with oxygen flowing through it. This allowed them to keep the tissue alive for up to 48 hours. During that time, they used a technique known as patch-clamp electrophysiology to measure how electrical signals travel along dendrites of pyramidal neurons, which are the most common type of excitatory neurons in the cortex.
These experiments were performed primarily by Beaulieu-Laroche. Harnett's lab (and others) have previously done this kind of experiment in rodent dendrites, but his team is the first to analyze electrical properties of human dendrites.
The researchers found that because human dendrites cover longer distances, a signal flowing along a human dendrite from layer 1 to the cell body in layer 5 is much weaker when it arrives than a signal flowing along a rat dendrite from layer 1 to layer 5.
They also showed that human and rat dendrites have the same number of ion channels, which regulate the current flow, but these channels occur at a lower density in human dendrites as a result of the dendrite elongation. They also developed a detailed biophysical model that shows that this density change can account for some of the differences in electrical activity seen between human and rat dendrites, Harnett says.
The question remains, how do these differences affect human brainpower? Harnett's hypothesis is that because of these differences, which allow more regions of a dendrite to influence the strength of an incoming signal, individual neurons can perform more complex computations on the information.
"If you have a cortical column that has a chunk of human or rodent cortex, you're going to be able to accomplish more computations faster with the human architecture versus the rodent architecture," he says.
There are many other differences between human neurons and those of other species, Harnett adds, making it difficult to tease out the effects of dendritic electrical properties. In future studies, he hopes to explore further the precise impact of these electrical properties, and how they interact with other unique features of human neurons to produce more computing power.
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Oct 18, 2018
|Dust density rendered simulation image of the disc -- white circle is inner dust ring.|
Finding real evidence that a planet is migrating (usually inwards) within such discs would help solve a number of problems that have emerged as astronomers are able to see more and more detail within protoplanetary discs. In particular it might provide a simple explanation for a range of strange patterns and disturbances that astronomers are beginning to identify within these discs.
Planet migration is a process that astronomers have known the theory about for 40 years but it's only now that they have been able to find a way of observationally testing if it really occurs. This new research from a team led by the University of Warwick, along with Cambridge, provides two new observational signatures in young solar system's dust rings that would be evidence of a migrating planet. That research will be published in the Monthly Notices of the Royal Astronomical Society.
The lead author, Dr Farzana Meru of the University of Warwick's Astronomy and Astrophysics Group in the Department of Physics, on the paper said:
"Planet migration in protoplanetary discs plays an important role in the longer term evolution of planetary systems, yet we currently have no direct observational test to determine if a planet is migrating in its gaseous disc. However the technology now available to us in the Atacama Large Millimeter/submillimeter Array (ALMA), is able to look deep into these discs, and even see detailed structures within the discs such as rings, gaps, spiral arms, crescents and clumps. ALMA can also use different millimetre frequencies to seek out concentrations of different particle sizes so we can also use it to explore the make up of individual dust rings within the disc"
"Our latest research has found a way to use this new technology to spot what we think will be a clear signature within these dust rings that the planet closest to them is actually migrating within that very young solar system."
The University of Warwick led research team have concluded that if ALMA looks at the two dust rings nearest the orbit of a planet a simple measurement of the typical particle size in each ring will reveal the answer.
If ALMA finds that the interior dust ring (i.e. between the planet's orbit and the star) is typically made up of smaller sized particles, and that the exterior dust ring (immediately outside of the planet's orbit) is typically made up of larger particles, then that will be clear evidence that the planet is migrating within the system's protoplanetary disc. The size of the particles would differ for each disc but in a case where the planet is located 30 astronomical units from the star and is 30 times the mass of the Earth, the smaller particles in the inner ring would typically be less than a millimetre in size, whereas those in the outer ring would be a little over a millimetre.
ALMA will be able to observe this because the wavelength at which it observes roughly correlates with the dust particle size. This means that as observers look at the disc with ALMA at increasing wavelengths, the interior dust ring is expected to fade, while the exterior ring would become brighter.
The reason for this pattern is twofold. Firstly the researchers' model shows that the exterior dust ring will contain more large dust particles because they move at a higher velocity (than the smaller particles) and are fast enough to keep up with the planet as it orbits inwards. This will result in a ring exterior to the planet's orbit that is mostly made up of large particles.
Secondly, the inner ring consists of small particles because they move inwards more slowly than the planet. Consequently they are unable to get out of the way of the inwardly migrating planet and so accumulate in a ring just inwards of the planet. This time the fast-moving large dust moves rapidly towards the star leaving an interior dust ring of small-sized particles.
The research team will continue to simulate what such ALMA observations would look like and astronomers can now use this method in their own ALMA observations to look for this two ring signature.
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|Fields of yellow flowers provide habitat for sweat bees.|
"Bees have complex social behaviors, and with this species of bee, we can directly compare individuals that live in social groups to those that don't live in social groups," said Sarah Kocher, an assistant professor of ecology and evolutionary biology and the Lewis-Sigler Institute for Integrative Genomics at Princeton University, who led the research. "We can ask: 'What are the fundamental differences between a social and nonsocial animal?'"
The researchers found that one of these differences involves the gene syntaxin 1a, which governs the release of chemical messengers in the brain. In all, the study found nearly 200 gene variations that were linked to social behavior, with 21 clustered in or nearby six genes implicated in human autism. The study was published in the journal Nature Communications.
Sweat bees are ideal for studying the genes underlying social behavior, Kocher said, because some are naturally social while others are solitary, even though both types belong to the Halictidae family. Both types nest in the ground, but the social bees live in a hierarchal society consisting of a queen and workers, like their honey bee relatives, while nonsocial sweat bees live alone.
Until Kocher began studying sweat bees, not many scientists had looked at the mechanisms underlying their behavior. One of the few scientists to have studied the bees was Cecile Plateaux-Quenu, an entomologist who in the 1960s documented sweat bee populations -- and their social habits -- in sites around France.
In 2010, Kocher located the retired scientist and eventually traveled to France to meet her. Plateaux-Quenu helped the younger scientist learn to identify the bees, find their nests, and net the insects as they traveled among the dandelions, asters and daisies.
Kocher, who was then a postdoctoral researcher at Harvard University, brought the bees back to the laboratory to analyze their genes. She sequenced the genomes of hundreds of bees of the species Lasioglossum albipes, known from locations that Plateaux-Quenu had classified decades earlier as home to either social or solitary bees. Next, the researchers looked through the genetic data to detect correlations between patterns of gene activity and social behavior.
The findings suggest that variations in several genes play a role in causing or contributing to the social behavior of these bees. Many of the variations detected were found in sections of the genetic code that are not genes themselves but rather regulate other genes by enhancing their activity.
Social behavior is complex and is determined by multiple genes rather than a single gene. Genes are important for brain development -- they orchestrate connections between neurons and pruning of those connections during development and childhood.
Another study conducted last year on honey bees also found a link between bee genes and autism genes. One of the differences between that study and this new one, Kocher said, is that honey bees are by nature social, whereas sweat bees can be either social or nonsocial.
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|A common cuttlefish (Sepia officinalis).|
Cuttlefish, squid and octopus are a group of marine mollusks called coleoid cephalopods that once included ammonites, today only known as spiral fossils of the Cretaceous era. Modern coleoid cephalopods lost their external shells about 150 million years ago and took up an increasingly active predatory lifestyle. This development was accompanied by a massive increase in the size of their brains: modern cuttlefish and octopus have the largest brains (relative to body size) among invertebrates with a size comparable to that of reptiles and some mammals. They use these large brains to perform a range of intelligent behaviors, including the singular ability to change their skin pattern to camouflage, or hide, in their surroundings.
Cephalopods control camouflage by the direct action of their brain onto specialized skin cells called chromatophores, that act as biological color "pixels" on a soft skin display. Cuttlefish possess up to millions of chromatophores, each of which can be expanded and contracted to produce local changes in skin contrast. By controlling these chromatophores, cuttlefish can transform their appearance in a fraction of a second. They use camouflage to hunt, to avoid predators, but also to communicate.
To camouflage, cuttlefish do not match their local environment pixel by pixel. Instead, they seem to extract, through vision, a statistical approximation of their environment, and use these heuristics to select an adaptive camouflage out of a presumed large but finite repertoire of likely patterns, selected by evolution. The biological solutions to this statistical-matching problem are unknown. But because cuttlefish can solve it as soon as they hatch out of their egg, their solutions are probably innate, embedded in the cuttlefish brain and relatively simple. A team of scientists at the Max Planck Institute for Brain Research and at the Frankfurt Institute for Advanced Studies (FIAS)/Goethe University, led by MPI Director Gilles Laurent, developed techniques that begin to reveal those solutions.
Cuttlefish chromatophores are specialized cells containing an elastic sack of colored pigment granules. Each chromatophore is attached to minute radial muscles, themselves controlled by small numbers of motor neurons in the brain. When these motor neurons are activated, they cause the muscles to contract, expanding the chromatophore and displaying the pigment. When neural activity ceases, the muscles relax, the elastic pigment sack shrinks back, and the reflective underlying skin is revealed. Because single chromatophores receive input from small numbers of motor neurons, the expansion state of a chromatophore could provide an indirect measurement of motor neuron activity.
"We set out to measure the output of the brain simply and indirectly by imaging the pixels on the animal's skin" says Laurent. Indeed, monitoring cuttlefish behavior with chromatophore resolution provided a unique opportunity to indirectly 'image' very large populations of neurons in freely behaving animals. Postdoc Sam Reiter from the Laurent Lab, the first author of this study, and his coauthors inferred motor neuron activity by analyzing the details of chromatophore co-fluctuations. In turn, by analyzing the co-variations of these inferred motor neurons, they could predict the structure of yet higher levels of control, 'imaging' increasingly more deeply into the cuttlefish brain through detailed statistical analysis of its chromatophore output.
Getting there took many years of hard work, some good insights and a few lucky breaks. A key requirement for success was to manage to track tens of thousands of individual chromatophores in parallel at 60 high-resolution images per second and to track every chromatophore from one image to the next, from one pattern to the next, from one week to the next, as the animal breathed, moved, changed appearance and grew, constantly inserting new chromatophores. One key insight was "realizing that the physical arrangement of chromatophores on the skin is irregular enough that it is locally unique, thus providing local fingerprints for image stitching" says Matthias Kaschube of FIAS/GU. By iterative and piecewise image comparison, it became possible to warp images such that all the chromatophores were properly aligned and trackable, even when their individual sizes differed -- as occurs when skin patterns change -- and even when new chromatophores had appeared -- as happens from one day to the next as the animal grows.
With insights such as this one, and aided by multiple supercomputers, Laurent's team managed to meet their goal and with this, started peering into the brain of the animal and its camouflage control system. Along the way, they also made unexpected observations. For example, when an animal changes appearance, it changes in a very specific manner through a sequence of precisely determined intermediate patterns. This observation is important because it suggests internal constraints on pattern generation, thus revealing hidden aspects of the neural control circuits. They also found that chromatophores systematically change colors over time, and that the time necessary for this change is matched to the rate of production of new chromatophores as the animal grows, such that the relative fraction of each color remains constant. Finally, from observing this development they derived minimal rules that may explain skin morphogenesis in this and possibly all other species of coleoid cephalopods.
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|Pando Grove in fall foliage at Dr. Creek Campground, Utah|
Rogers and McAvoy, in a PLOS ONE publication released 17 October, 2018, show Pando, Utah's massive, yet imperiled, aspen clone, is in grave need of forest triage. Early protection from fencing showed great promise in abating browser impacts, which have nearly eliminated recruitment of young aspen stems for decades now. However, follow-up fencing of a larger area (in combination with about half of Pando remaining unprotected by fencing) is currently failing according to this study. "After significant investment in protecting the iconic Pando clone, we were disappointed in this result. In particular, mule deer appear to be finding ways to enter through weak points in the fence or by jumping over the eight-foot barrier," says Rogers, Director of the Western Aspen Alliance and Adjunct Faculty member in USU's Wildland Resources Department. He further adds, "While Pando has likely existed for thousands of years -- we have no method of firmly fixing its' age -- it is now collapsing on our watch. One clear lesson emerges here: we cannot independently manage wildlife and forests."
In addition to presenting the first comprehensive analysis of forest conditions, the study offers a unique 72-year historical aerial photo sequence the visually chronicles the a steady thinning of the forest, past clear-cuts that remain deforested today, and continual intrusion of human development. Taken as a whole, objective analysis and the subjective photo chronology reveal a modern tragedy: the "trembling giant" that has lasted millennia may not survive a half-century of human meddling.
Pando is widely considered the world's largest single organism weighing in at an estimated 13 million lbs. (5.9 million kg). Covering some 106 acres (43 ha) in south-central Utah's Fishlake National Forest, the clonal colony consists of more than 47,000 genetically identical above-ground stems or "ramets" originating from a single underground parent clone. Quaking aspen, Pando's iconic species, was named Utah's State Tree in 2014 and, among numerous values, is considered a staple of scenic montane landscapes in the American West. Rogers sees trends found at Pando occurring across the western states, thus the Western Aspen Alliance serves as a clearinghouse of contemporary aspen sciences for professionals, scientists, and policymakers.
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Oct 17, 2018
Already today, a large number of the altogether 49 World Heritage Sites investigated are at risk due to rising sea levels. Up to 37 of these sites are at risk from a so-called 100-year storm surge, which has a 1 percent chance of being exceeded in any given year. 42 of the 49 sites are at risk from coastal erosion. If sea levels continue rising further, "in the Mediterranean region, the risk posed by storm surges, which are 100-year storm surges under today's conditions, may increase by up to 50 percent on average, and that from coastal erosion by up to 13 percent -- and all of this by the end of the 21st century under high-end sea-level rise. Individual World Heritage Sites could even be affected much more due to their exposed location," said Lena Reimann to explain the study results.
In order to be able to evaluate the potential risks, the research team created a spatial database of all UNESCO World Heritage Sites in low-lying coastal areas of the Mediterranean region. In addition to the location and form of the sites, the study also included the heritage type, the distance from the coastline, and its location in urban or rural surroundings. "Using this database and model simulations of flooding, taking into account various scenarios of sea-level rise, we were able to develop indices: the index for flood risk and for erosion risk," said Reimann. The flood risk index takes into account the potentially-flooded area and the maximum flood depth of each World Heritage Site. The erosion risk index is based on the distance of each site from the coastline and the physical properties of the coast, which largely determine the degree of erosion. These include, among others, the material properties of the coast, from sandy through to rocky, and the availability of new sediment.
The increase in flood risk of up to 50 percent and erosion risk of up to 13 percent are based on an assumed average sea-level rise in the Mediterranean region of 1.46 meters by the year 2100. This increase could occur with a five percent probability (95th percentile) under a high-end climate change scenario (RCP8.5). "Even if such a high sea-level rise has a low probability of occurring by the year 2100, this scenario cannot be ruled out, due to the high uncertainties in relation to the melting of the ice sheets," said Professor Vafeidis. "In addition, such a scenario is quite relevant from a risk management perspective, since a 5% probability in this context is not low."
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|When dandelion seeds fly, a ring-shaped air bubble forms as air moves through the bristles, enhancing the drag that slows their descent.|
The discovery, which confirms the common plant among the natural world's best fliers, shows that movement of air around and within its parachute-shaped bundle of bristles enables seeds to travel great distances -- often a kilometre or more, kept afloat entirely by wind power.
Researchers from the University of Edinburgh carried out experiments to better understand why dandelion seeds fly so well, despite their parachute structure being largely made up of empty space.
Their study revealed that a ring-shaped air bubble forms as air moves through the bristles, enhancing the drag that slows each seed's descent to the ground.
This newly found form of air bubble -- which the scientists have named the separated vortex ring -- is physically detached from the bristles and is stabilised by air flowing through it.
The amount of air flowing through, which is critical for keeping the bubble stable and directly above the seed in flight, is precisely controlled by the spacing of the bristles.
This flight mechanism of the bristly parachute underpins the seeds' steady flight. It is four times more efficient than what is possible with conventional parachute design, according to the research.
Researchers suggest that the dandelion's porous parachute might inspire the development of small-scale drones that require little or no power consumption. Such drones could be useful for remote sensing or air pollution monitoring.
The study, published in Nature, was funded by the Leverhulme Trust and the Royal Society.
Dr Cathal Cummins, of the University of Edinburgh's Schools of Biological Sciences and Engineering, who led the study, said: "Taking a closer look at the ingenious structures in nature -- like the dandelion's parachute -- can reveal novel insights. We found a natural solution for flight that minimises the material and energy costs, which can be applied to engineering of sustainable technology."
From Science Daily