EARTH SCIENCE geology, the environment, and the universe 2008 (32)

Swim the Okavango Explore the African Landscape Dig for Dinosaurs W hat is it like to scuba dive with crocodiles in the Okavango delta? Or fly in a bush plane over the African continent? Or dig for dinosaurs in China? The National Geographic Expeditions allow you to share in the excitement and adventures of explorers, scientists, and environmentalists as they venture into the unknown Each Expedition takes you on a journey that enriches your learning about our dynamic planet 890 David Doubilet/National Geographic Image Collection eXpeditions! Table of Contents 892 Tracing the Human Footprint 898 State of Rock 904 Okavango 910 Super Storms 916 The Next Big One 922 Jewels in the Ash 928 Frogs 934 Night Vision Use with Chapter Use with Chapters and Use with Chapters and 10 Use with Chapters 11 and 13 Use with Chapter 19 Use with Chapter 21 Use with Chapter 26 Use with Chapters 27 and 28 For more information on these Expeditions, visit glencoe.com You can also link to original National Geographic articles that cover these topics and more 891 George Steinmetz/National Geographic Image Collection 892 NG Maps/National Geographic Image Collection Peter Ragg eXpeditions! Africa by Air Tracing the Human Footprint From a low-flying plane is how ● ABOVE: Biologist J Michael Fay catches some sleep after eight hours in the air On board this and another Cessna, Fay, pilots, photographers, and others risk their lives to map humanity’s impact on tropical forests, savannas, and deserts Along the way on this “Megaflyover” they struggle against malaria, sandstorms, and brushfires and try to keep the planes, computers, digital cameras, and GPS systems running ● LEFT: The map of Africa shows the zig-zag route taken by Michael Fay during a joint project—the Human Footprint—of the Wildlife Conservation Society (WCS) and the National Geographic Society J Michael Fay sees the land on a mild December morning, as an heirloom Cessna 182 carrying him and three others approaches the Aïr Massif, a vast range of highlands standing up from the Sahara The Cessna is painted scarlet and specially equipped for collecting data The plane looks like a toy, or an enameled piñata, but it bears serious purposes, not candy With a young Austrian pilot named Mario Scherer at the controls, and Fay in the right seat amid a rat’s nest of custom-rigged digital hardware and cables, it caresses the topography, circling here, dipping a wing there, rising nervily through high notches to put peaks close at eye level on each side Mounted in its right door is a high-resolution digital camera that automatically, every 20 seconds, takes a vertical shot of the ground The photos, each tagged with Global Positioning Satellite (GPS) data registering exact time, latitude, longitude, and altitude, are uploaded into a computer on Fay’s lap, through which he can add notes A similar computer, scrolling out a map along the plane’s flight line, rests under his left elbow Fay’s attention flicks constantly, tirelessly, between the computer screens and the terrain passing below 893 ● ABOVE: The Namib Desert is just one of the 104 terrestrial ecoregions identified in Africa Among Earth’s driest places—and perhaps the oldest desert—it boasts orange sand dunes made sharp and steep by the blowing wind ● BELOW: The Ituri Forest in the Congo is a vastly different type of ecoregion from the Namib Desert in terms of the amount of rainfall, types of vegetation, and animal life The Realities of Land Use Today is our tenth day of survey flying in Niger, and the 187th day since Fay and his chief pilot, Peter Ragg, departed from an airfield in South Africa Fay’s aerial enterprise is closely linked with an ambitious initiative of the Wildlife Conservation Society — the Human Footprint project That project involves a program of multidimensional mapping to show gradients of wildness and human impacts around the world Fay himself, a restless individualist with a surprisingly good nose for politics, wants nothing less than to change the way the world perceives and uses ecosystems and natural resources — starting with perceptions in Washington, D.C The ultimate goal of his Africa Megaflyover, he says, is to convince “the powers that be, in particular the U.S Congress,” that integrating natural resource management into American foreign policy is “a very, very smart thing to And a good investment.” Wherever humans live at high population densities, making unsustainable demands on natural systems, he notes, you eventually see ecological breakdown Unmet needs and tensions lead toward conflict A pilot himself, he recognized the value of low-altitude flying to illuminate the realities of land use 894 (t)George Steinmetz/National Geographic Image Collection,(b)George Steinmetz/National Geographic Image Collection George Steinmetz/National Geographic Image Collection eXpeditions! A bush plane shows you patterns you’ll never perceive from the ground It allows flexibly targeted coverage (“Let’s circle that spot again”) and the capture of fine details you can’t get from a satellite Africa, the continent he knows and loves best after 25 years of working there, was the logical place What Is Africa? Of course Africa isn’t really a place; it’s a million places Nowadays it encompasses 47 countries (not counting Madagascar and other islands) with a total population of 900 million humans It can also be parsed into 104 terrestrial ecoregions, each unique in its physical and climatic features Each one harbors a distinct plant and animal community Ecoregions in many cases transcend national boundaries Within or near all ● ABOVE: Lake Natron straddles Tanzania and Kenya Along Kenya’s section of the lake, microorganisms living in the water’s salty crust create a palate of these ecoregions live people whose most pink Pigments in the organisms cause the feathers of the flamingos that elemental struggles and aspirations trandepend on the lake for food to turn pink scend ecological boundaries as well as national ones Africans want better and None of these concerns is unique to Africa fuller employment They want food But Africa particularly deserves special attention security and education for their children They Africa’s glories and successes deserve special attenwant good governance, free of oppression and cortion, too African peoples produce magnificent art, ruption They want fair, sensible arrangements for graceful cultures, terrific music, great works of the the management of wild landscapes and natural resources — arrangements chosen and controlled by mind, and astonishing acts of political and moral courage Africans They want peace Along with the human struggles come human impacts Although some areas of Africa are less Documenting Ecological Dimensions heavily inhabited than they might be, others are Fay’s intent is to document the ecological dimenoverburdened, eroded and blighted by the presence sions of that variousness His conceptual starting and demands of too many people Because the point was the World Wildlife Fund map of 104 African landmass is so large, climate change may African ecoregions and the Human Footprint projaffect its interior regions by bringing considerably ect, conceived by Eric W Sanderson and a team of higher temperatures and worse droughts and floods This contributes to increased desertification colleagues at the WCS and Columbia University and new patterns of disease Poaching wildlife, both Sanderson’s group used nine different geographic for subsistence and commercially, is an old problem data sets (measuring factors such as road density, railways, population density, nighttime lighting) to but still serious Timber harvesting, even when represent the weight of human influence all over done selectively, often brings workers who empty the planet, including Africa a forest of its fauna for bush meat 895 ● ABOVE: A herd of buffalo is seen wallowing in the muddy swamps of the Zambezi Delta in Mozambique Protection efforts there seem to have buffalo populations increasing Beginning the Megaflyover ● ABOVE: View of an area near the Mahajamba River on Madagascar reveals a rocky terrain Madagascar is considered a hot spot for conservation because its unique flora and fauna are found nowhere else and there are tremendous population and resource pressures on the land 896 The first takeoff was on June 8, 2004, from Swartkop Air Force Base near Pretoria Soon after,— OK, it was five minutes — Fay’s network of digital gizmos suffered an outage The camera quit, the computers went to battery power, and he sniffed a hint of electrical fire Oh well, he thought, better a data-system meltdown than full-on engine failure within sight of the runway He re-rigged Hopping his way across southern Africa and then northward on a chain of one-day flights, Fay arranged collaborations wherever possible He assisted local conservationists, field scientists, or national agencies with their aerial-survey needs as well as adding data to his own comprehensive trove Wherever he went, Fay tried to complement the aerial data-gathering with contacts, conversations, and observations on the ground Many computer crashes, camera shutdowns, and other minor problems have followed that first glitch above Swartkop Most were easily repaired There have also been a few dire aviation scares, caused by high winds, drastic loss of oil pressure, and other forms of mischance (t)George Steinmetz/National Geographic Image Collection, (b)George Steinmetz/National Geographic Image Collection Fay wanted to cover as many of the 104 regions as time, budget, and politics would allow Then he would present an enormous body of data — between what is possible to what is actually happening — to decision-makers and say: Here’s some information that might be relevant to your resources-andsecurity planning Fay recruited Ragg, an experienced bush pilot (and, in an earlier life, a successful optometrist in Austria), who offered his flying skills and the use of his two vintage airplanes, one for primary data gathering, one for support Ragg in turn enlisted his fellow Austrian, Mario Scherer, who had found African bush flying a lively change from his recent work as a war-crimes investigator in Kosovo Fay drummed up support from various sources—the Human Footprint lab at WCS, the WILD Foundation, the Bateleurs (an Africa-based organization of bush pilots volunteering for conservation), and, as chief financial sponsor, the National Geographic Society (t)George Steinmetz/National Geographic Image Collection, (c)George Steinmetz/National Geographic Image Collection eXpeditions! By the time I [David Quammen] met them in Niger, Fay and his pilots had flown 600 hours, crisscrossing 16 countries, usually at about 150 meters (500 feet) above the ground One of the Cessnas had gotten a new engine Both planes needed maintenance Theme of Absence From the air over Niger we enjoyed some notable sights A pair of addaxes skittered like sand crabs along a linear dune Seven Barbary sheep galloped up sausage-like towers of dark sandstone along the Djado Plateau Camels stood stuporous and serene in the middle of nowhere Near one village we gawked down at a cluster of saltmaking pits Each pit, a nice disk, variously sized, shone azure or turquoise or coppery green from the mineral solutions of their individual sumps — all together a necklace of bright-colored jewels Mostly what we observed and recorded, though, were variations on a theme of absence Some days we flew a 650-kilometer (400-mile) loop without glimpsing a single animal, and dozens of miles without spotting so much as a plant Even absence is a form of data Niger is a country desolated by recent human-caused losses The addax is nearly extinct here, for instance, and the Barbary sheep, and the desert cheetah Their disappearance from remote habitat areas may correlate with the presence of four-by-four tracks, indicating unimpeded access by poachers Such tracks show clearly from 150 meters (500 feet) up Another sight came into view: a large green oval It was a pond, evidently spring-fed from beneath the sands Water? Fay peered down for a moment, having noticed something, tapped a note into his computer: “no animal tracks.” It hadn’t struck me, ● ABOVE: An old abandoned town north of Dirkou, Niger, is built of blocks of salt The houses without roofs reveal room after room, some only a few feet square Newer towns are built of mud brick and have satellite dishes and telephones ● LEFT: Casablanca, Morocco, is an enormous place, with miles and miles of buildings Water availability is evident from the green vegetation but of course: A water hole out here should attract gazelles and other mammals from many miles around — attract them, that is, if any exist He tapped again: “4x4.” Meaning, tire marks An absence of animal sign, a presence of human sign Cause and effect? Anyway, data The challenge for Fay is that he must deliver meaning from the mountainous pile of facts and photographs he has collected eXpeditions activity Consider the kind of variation there must be to have 104 distinct ecoregions in Africa Verbally illustrate an ecoregion by listing and describing some of its factors 897 898 Frans Lanting/National Geographic Image Collection eXpeditions! Where the Elements Reign` State of Rock ● RIGHT: Blasted by wind, broken by water, the Colorado Plateau spreads across 336,700 square kilometers (130,000 square miles) of Arizona, New Mexico, Utah, and Colorado This arid expanse, best seen by air, has been called useless by some, a landscape that conspires against human settlement For others it’s nature’s grandest work in progress ● LEFT: Hoodoos are columns of rock in fantastic shapes that are found in western North America These appear in Utah’s Bryce Canyon National Park Bizarre Is that the right word for the Colorado Plateau, this thirsty sprawl of gaudy-hued stone festooned with such names as Hell Roaring Canyon, Scorpion Gulch, and Horsethief Point? Edward Abbey began his classic Desert Solitaire with the simple “This is the most beautiful place on earth.” Fiery rock can that to a person Others trying to understand the attraction of the plateau country apply adjectives like “amazing” and “awesome.” In truth, a single adjective may not suffice All the same, as I [Mike Edwards] fly over the plateau on a May morning, looking down on whalebacks of slickrock, on crashing waves of rock, on minarets and pyramids of rock hewn by water and wind—how could any word fit better than “bizarre”? 899 NG Maps/National Geographic Image Collection (tr)O Louis Mazzatenta/National Geographic Image Collection, (cl)Art by Mark Dubeau/National Geographic Image Collection, (cr)Art by Mark Dubeau/National Geographic Image Collection, (bl)O Louis Mazzatenta/National Geographic Image Collection, (br)O Louis Mazzatenta/National Geographic Image Collection eXpeditions! Predator-Prey Relationships Liaoning is situated within a vast region whose primeval flora and fauna are referred to as the Jehol biota The area was characterized by a warm climate and numerous lakes These conditions provided a fruitful environment for plants and animals to differentiate and flourish So many individual fossils have been found that scientists are able to study population dynamics, succession within communities of interacting species, and even predator-prey relationships ● LEFT: A small fish lies next to the head of a fossilized specimen of Hyphalosaurus lingyuanensis, as if predation had been cut off by the sudden death of both predator and prey That the animal, just under four feet long, was indeed a fish-eater is suggested by its small head, needlelike teeth, and pointed snout Hyphalosaurus, which inhabited freshwater, bears a resemblance to Plesiosaurus, a marine creature, in an example of convergent evolution — when distantly related creatures evolve similar traits in similar environments ● LEFT: Scientists who have long known that dinosaurs preyed on mammals were stunned by the discovery of a fossil that turned the tables Found by villagers, the cat-sized mammal’s skeleton contains the remains of its last meal: a young beaked dinosaur called Psittacosaurus Uncertainties remain about the behavior of Repenomamus robustus, says Hu Yaoming of the IVPP ”Did it catch the dinosaur after a pursuit? If so, that suggests it was active in daytime when the dinosaur would also be active But if it was a scavenger, it could have eaten it day or night.” With large pointy teeth and powerful jaws designed for catching and ripping prey, R robustus shows that Mesozoic mammals could compete with the smaller dinosaurs for territory — and food Its stomach contents, shown in the inset at the right, included a hind limb of the young beaked dinosaur, along with a forelimb and several teeth These bones are well articulated — still joined to other bones in their natural positions — suggesting that R robustus, rather than chewing, swallowed food in chunks 925 Bird-Dinosaur Relationships “The site preserved not just bones but often whole skeletons,” says paleontologist Hans-Dieter Sues of the Smithsonian Institution, “and some birds were preserved so well you can distinguish between male and female Liaoning is unique.” During the 1990s Liaoning jumped from the pages of scholarly journals onto front pages everywhere through a series of spectacular discoveries of archaic birds and — more intriguingly — dinosaurs with feathers These fossils bolstered the once controversial but now widely endorsed theory that modern-day birds descended from dinosaurs They also provide much new evidence in the ongoing debate about how flight originated Fossils are being uncovered faster than paleontologists can describe the specimens and spread the new knowledge through scientific papers And Liaoning promises to provide fresh discoveries for many years to come 926 (l)Mark Leong/National Geographic Image Collection, (r)Art by Mark Dubeau/National Geographic Image Collection ● BELOW: In death a pterosaur rests with a wing bone in its mouth, perhaps from the natural collapse of the wing, perhaps, as some scientists speculate, from a struggle before volcanic gases snuffed out its life The pointed beak and the sharp and slender front teeth suggest that it preyed on fish Long before bird and bats took wing, the skies were ruled by pterosaurs, reptiles that were Earth’s first flying vertebrates They arose 230 million years ago during the later part of the Triassic Period and thrived for 165 million years until going extinct at the end of the Cretaceous Period The wingspan of Hoopterus gracilis was nearly four and a half feet, easily exceeding the ten-inch span of Pterodactylus elegans, perhaps the smallest pterosaur, but falling far short of Quetzalcoatlus northropi, whose wings stretched at least 36 feet tip to tip The pterosaurs’ light, hollow bones aided takeoff But their fragility also made fossilization difficult — best achievable in the soft ooze of the seafloor or lake beds like those at Liaoning The discovery of H gracilis and other pterosaurs at Liaoning, some preserved with body coverings of fuzz, extends the known range of pterosaurs (l)Mark Leong/National Geographic Image Collection, (r)Art by Mark Dubeau/National Geographic Image Collection eXpeditions! ● ABOVE, RIGHT: In a rare instance of a vertebrate’s behavior being revealed by its fossil, a new species of troodontid dinosaur was found with its head tucked under a forelimb It represents the earliest known example of a dinosaur displaying the sleeping posture exhibited by modern-day birds The “tuck-in” pose would have preserved body heat, suggesting that, like birds, at least some dinosaurs were warm-blooded Delighted paleontologists named the pigeon-size creature Mei long, meaning “soundly sleeping dragon.” Though it is not known how the dinosaur died, it probably was killed instantly by a thick deposit of volcanic ash or by volcanic gas followed by a covering of ash and mud Mei long adds to the ever increasing evidence of birddinosaur kinship eXpeditions activity Reread the article and make a chart of recent discoveries made at the Liaoning fossil site, naming the discoveries, evidence, and new knowledge, as in the example given Compare your chart with that of a partner Discuss any differences and how your charts could be changed to be more accurate Discovery new species of troodontid dinosaur Evidence skeleton with head tucked under forelimb New Knowledge Earliest known example of posture of modern-day bird, suggesting some dinosaurs were warm blooded 927 928 George Grall/National Geographic Image Collection George Grall/National Geographic Image Collection eXpeditions! The Fragile World of Frogs Stephen Richards, an Australian herpetologist, has ● ABOVE: This young red-eyed tree frog (Agalychnis callidryas) has newly emerged from a pond As a tadpole, this frog survived dragonflies, water beetles, fish, and shrimps As an adult, it must evade bats, birds, snakes—and humanity’s hunger for land ● LEFT: Life and strife begin together as a tiny froglet (Oreophryne sp.) hatches fully formed, bypassing the tadpole stage Miraculously diverse—and in serious decline—frogs signal that something’s amiss in the natural world spent a good deal of his life traversing the woods of Papua New Guinea (PNG) and Queensland, Australia, searching out frogs— and has dozens of new species to show for his efforts “If you want to catch frogs, you’re going to be out at night.” But not just any night Rain is generally a necessity too To a frog the steady spatter is a signal that it’s time to find a mate Male frogs gather near streams and ponds to call to the females The males’ songs have another, coincidental use: They help scientists like Richards find them Richards said, “If they’re not calling, they can be very difficult to find.” Finding frogs has always been a basic herpetological skill But in the past two decades that skill has taken on added importance Increasingly it has become a key tool for monitoring the health of frog populations and species and for helping to identify the causes of some species’ precipitous decline Here, in PNG, the frogs seem healthy, their populations stable “But what we really know about their populations?” asked Richards “We’re just now beginning to identify the species that live here That’s the situation in many places We could be losing frogs that we’ve never seen.” Variations in Frog Habitats Like a man on a mission, Richards waded into a stream, clambered up a waterfall, and disappeared into the woods Only moments later he reappeared near the top of the fall “Look at this!” he shouted over the rushing water “[This female had] started her journey to the stream, where she’ll lay her eggs,” he said Her chosen male will fertilize the eggs as they emerge from her cloaca “But look where she plans to put her eggs—here in this rushing current It seems the most inhospitable place for a frog to lay eggs or for tadpoles to live.” 929 The torrent-stream frog’s tadpoles thrive in this tumultuous environment because they have evolved enlarged mouths with suction lips that enable them to stick to the surface of a rock while grazing on the algae growing there Where the going was tough for an animal like a frog, they’d been extremely successful, so much so that there were numerous torrent-stream species here One of the joys of frog-watching is discovering the many variations frogs have evolved for the basics of life Frogs were always turning up in places—dry deserts, cold mountains, plunging waterfalls— where they shouldn’t be Their ancestors, the first amphibians, arose some 350 million years ago Amphibians were the first animals with backbones to walk on land Some were large, crocodile-size creatures, but over time they evolved into the three orders of smaller animals known today: the Anura (frogs and toads), Caudata (salamanders and newts), and Gymnophiona (caecilians, wormlike creatures that live in leaf litter or streams) Anurans, the frogs and toads, are the most successful living amphibians, with some 4500 species now known, a count that’s been steadily growing because in the past few years scientists have ferreted out more than 50 new species annually Like most amphibians, frogs spend at least part of their lives in water It might seem that that would limit where they can live, but frogs are found from Arctic tundra to the driest of deserts and from sea-level mangrove swamps to the 18,000-foot-high Tibetan Plateau To survive in such extreme environments, frogs have evolved an impressive range of adaptations The North American wood frog (Rana sylvatica), for instance, can survive freezing temperatures for as long as seven months, relying on a natural antifreeze in its blood to protect its organs Some species in the dry forests of South America secrete a waxy coating to protect themselves from drying out, while the waterholding frogs of Australia store water in their bladder and under their skin for use during droughts Another Australian frog, shaped like a fat turtle, spends most of its life burrowed beneath termite mounds in arid deserts, where it feeds on nothing but termites Reproductive Behaviors Equally intriguing are frogs’ reproductive behaviors Many frogs and toads have a multi-stage life, that passage from tadpole to adult called metamorphosis There are at least a dozen ways frogs can make that journey The standard method begins with fertilized eggs in a pond; the tadpoles hatch, feed on algae, and change into frogs Many other species have evolved methods that bypass the pond In Queensland’s Paluma Range National Park, Adam Felton, a colleague of Richards’s at James Cook University, has been watching a number of ornate nursery frog (Cophixalus ornatus) males “Cophixalus is a microhylid,” Felton explains, “and all Australian microhylids have what we call direct development.” In other words the microhylid froglets develop inside the egg Felton shines his headlamp on a patch of earth “See this little hollow? That’s the male’s nest, and those little clear balls are the eggs he’s guarding—or should be, if he was here.” Dad should be hunkering down on top of those eggs “That protects them, keeps them moist, and may even prevent fungi and bacteria from growing on them.” In South America, male Darwin’s frogs slurp up the fertilized eggs and hold them in their vocal sacs until the froglets emerge In other species females provide the parental care The female poison dart frog (Dendrobates pumilio) not only attends her eggs but also transports the hatched tadpoles to pools in tree holes or within the inner leaves of bromeliads She visits her offspring to lay unfertilized eggs Newly laid green eggs of the red-eyed tree frog, adjoin a clutch whose for them to eat The female Surinam toad (Pipa embryos will soon hatch If attacked by snakes or wasps, the tadpoles can pop out early, escaping to water below pipa), an aquatic species, converts her entire 930 George Grall/National Geographic Image Collection Rachel Ivanyi/National Geographic Image Collection eXpeditions! back to a nursery She and the male swim end over end, transferring the fertilized eggs to pouches in her back Her skin grows over the eggs, sealing them in until the froglets hatch Even tadpoles left on their own sometimes have protective devices In Panama, Stan Rand, a herpetologist with the Smithsonian Tropical Research Institute, guides me to a pond where the tree frog Agalychnis callidryas has laid masses of gelatinous eggs on palm fronds These are a favorite food of an arboreal snake, but when the snake bumps the eggs, the tadpoles hatch prematurely “It’s a 50-50 chance for them,” says Rand “They’ll still face predators in the pond, but if they don’t hatch, they’ll be eaten by the snake.” As wonderful as all these adaptations are, none is— or was—as remarkable as that of Australia’s gastricbrooding frogs, Rheobatrachus Researchers invariably mention the two species in this genus as the most astonishing example of what frogs can The females of this two-inch-long stream dweller swallowed their fertilized eggs or tadpoles, shut down their digestive systems, and hatched their young in their stomachs About a month later the mother opened her mouth and regurgitated her tiny froglets ● ABOVE: No one has seen a gastric brooder in the wild since 1981, and none are in captivity They are apparently extinct Die-offs in Australia Keith McDonald, the chief ranger with Queensland Parks and Wildlife Service, had helped monitor the two known populations of gastric brooders shortly after they were first discovered about 25 years before “I’d been watching this population; I went back three months later,” McDonald recalls He searched for frogs; none were to be found Since the 1970s, more than a dozen Queensland frog species, especially the stream-dwelling types, have experienced sudden, massive die-offs In some cases, such as in these remote Queensland mountains, certain frog populations vanished in a few short months Something in the environment was adversely affecting frogs, but no one was certain what it was or how many factors were to blame Now, after intensive study and monitoring programs, researchers have some strong clues Some of the best leads for the mass deaths have come from the Queensland rain forests Richards and others realized something was wrong with the Queensland frogs shortly after he started a study project in Paluma Range National Park in 1989 That year four species of frogs lived in the clear waters of Birthday Creek Less than two years later two of the frog species—a lace-lid tree frog and a torrent frog similar to those in PNG—had vanished Elsewhere in Queensland, McDonald had noticed that the population of another species, a day frog, which had lived alongside the gastric brooders, was beginning to dwindle “We’d never paid much attention to the day frogs because we were all fascinated by the gastric brooders,” says McDonald “And the day frogs were about as common as fleas on a dog’s back Then phhht! They were gone too.” In 1993 McDonald and other researchers happened to find some of the day frogs as they were dying, one of the first times that frogs had been spotted in the throes of a massive die-off They collected some and sent their remains to Rick Speare, an infectious disease specialist at James Cook University 931 Die-offs in the Americas While the Australian frogs were disappearing, frogs in the rain forests of Costa Rica’s mountains also began to dwindle Most alarmingly the splendid Costa Rican golden toad (Bufo periglenes) vanished Not one has been seen in the wild since 1989 Other frog species disappeared in that habitat too, but not until 1996 did a scientist chance upon a dying population That year Karen Lips, a herpetologist at Southern Illinois University, found dead and dying frogs in the high rain forests of Panama, and like McDonald, she dispatched them to a disease expert These specimens, together with those from Australia and others from the National Zoo in Washington, D.C., led to the discovery of a previously unknown frog killer: a waterborne organism called a chytrid (KI trid) fungus Most chytrids are simply decomposers of plant materials Some are known to live as parasites on plants and invertebrates, but this species is the first discovered to kill vertebrates Scientists not know how the ● BELOW: Lips and Robertson catch, weigh, and measure the frogs, then gently scissor off one back toe—which does not cripple the frog Lips takes the toe clips because they may help us learn more about chytrids In particular, researchers hope to discover why some species are susceptible to it and others are not chytrid kills frogs Speare suspects that the fungus may release a toxin as it eats the keratin (a protein) in the frog’s skin “We’re looking at a newly introduced disease, an emerging pathogen,” Speare said The fungus has been found on 44 Australian frog species and appears to have caused the extinction of four, including the gastric brooders And several U.S frog species are now known to have died from the disease The chytrid is suspected as the main cause of the sudden declines in frog populations in mountainous regions of Central and South America But researchers still not know where the chytrid originated or how it arrived in the Americas or Australia or how they can stop its spread in the wild The discovery of the lethal chytrid is all the more troubling because many of the frogs at highest risk of succumbing to the disease live in places that people have set aside for their protection In the dense rain forest of Panama’s Omar Torrijos National Park, Karen Lips hikes up a rocky stream, counting frogs and toads with her graduate assistant, Jeanne Robertson Lips thinks the chytrid killed Costa Rica’s toads and other montane frogs She found frogs dying from the disease at another Panamanian site and worries that it may have reached this park Our first day of surveying, however, dispels her fear Only a few minutes down the trail, Robertson calls out “Frog!” simultaneously bending down to grab her prize She reveals a three-inch-long golden frog There’s nothing subtle about this hue, and Lips explains that it serves as a warning to potential predators: The frog’s skin is laden with lethal poisons We find numerous frogs, including several tiny golden frog babies Lips’s survey will also begin fleshing out the baseline list of frogs found in this park “That’s the thing about frogs,” she said “There’s still so much basic work that needs to be done Dozens of new species are found every year, and we know so little about any of them.” Protecting Frogs The Chiricahua leopard frog (Rana chiricahuensis), once common throughout the Southwest, has nearly vanished from several desert canyons—but has found protection on a rancher’s land Matt Magoffin discovered a healthy population of them 932 George Grall/National Geographic Image Collection George Grall/National Geographic Image Collection eXpeditions! North A America B E Europe C Asia Africa D G South America ● ABOVE: Examples of environmental changes that contribute to a decline in frog populations: (A) ULTRAVIOLET RADIATION: Ultraviolet light can alter DNA cells and suppress immune responses Biologists think UV radiation contributed to massive die-offs of frogs’ eggs in Oregon (B) INTERSPECIES COMPETITION: Non-native fish and voracious bull-frogs stocked for food and sport devour native frogs and their prey Such actions have nearly wiped out the mountain yellow-legged frog in California (C) PARASITES, PESTICIDES: Gruesome deformities have appeared in Canada and the northern U.S Trematode parasites and pesticides and their by-products are suspected (D) CLIMATE CHANGE: Populations of the golden toad, once found in Costa Rica, collapsed when dry weather pushed moisture-giving clouds beyond the habitat Biologists blame global warming (E) POLLUTION: The highly permeable eggs and skin of frogs easily admit toxic substances Acid rain has caused frog declines in Britain, Canada, Scandinavia, and Eastern Europe Heavy metal, fertilizer compounds, and agricultural chemicals also take a toll (F) HABITAT DESTRUCTION: As humans cut trees, drain marshes, pave meadows, and dam rivers, frogs die The world over, habitat loss and alteration is by far the greatest cause of death for frogs—creatures of limited range that can’t easily relocate (G) OVERHARVESTING: Millions of frogs die each year to supply restaurants with frog legs Most come from Indonesia India and Bangladesh banned exports after frog declines led to a rise in mosquitoes, malaria, and pesticide use (H): DISEASE: Saprolegnia, chytrid, iridovirus—such diseases are affecting frogs worldwide F Australia H in a large cattle tank During a bad drought Magoffin trucked a thousand gallons of water every week to the tank to keep the frogs going Now conservationists are using the Magoffin frogs to restock other areas Frogs—Sentinel Species Frogs have thrived from the tundra to the tropics for 190 million years Now they are vanishing—rapidly and perhaps irretrievably Why? Habitat loss is only the most obvious villain Additional causes remain unclear, particularly in Asia, Africa, and other regions where research has been minimal Scientists warn that climate change, pollution, and other factors may be acting together to deform and kill frogs Frogs are regarded as “sentinel species” in ecosystems because of their intimate contact with air, water, and earth “We share the planet,” says Mike Lannoo of the Declining Amphibian Populations Task Force “If something out there is affecting frogs, there’s a chance it’s affecting us too.” eXpeditions activity Research the current status of three of the frogs discussed in the article Make a list of changes in environmental conditions since this article was written that contribute to an increase in the frogs’ populations or add to their decline 933 934 NASA/JPL/CALTECH/Lori Allen and Joseph Hora, Harvard Smithsonian Center for Astrophysics eXpeditions! NASA’s Spitzer Space Telescope Night Vision ● ABOVE: Most space telescopes orbit the Earth, but Spitzer orbits the Sun, trailing Earth by 41.8 million kilometers (26 million miles) — a gap that increases by 17.7 million kilometers (11 million miles) every year The distance keeps the telescope far from the disruptive heat of our planet and reduces the Earth and Moon to mere dots, giving Spitzer an uninterrupted view of large sections of the sky ● LEFT: New stars blaze in a cloud of dust and gas 50 light-years across and 7000 light-years away Ultraviolet radiation from a nearby massive star sculpted the cloud into pillars and canyons; then gravity squeezed the denser clumps until stars burst to life, like those atop the pillars The Spitzer Space Telescope made this image at infrared wavelengths invisible to human eyes There’s a lot hiding in the universe’s dark corners Interstellar dust clouds and inky stretches of deep space can appear dull to ordinary telescopes But to a car-sized telescope 41.8 million kilometers (26 million miles) from Earth, they are alive with light — infrared light, or heat rays Since its launch in August 2003, says Robert Kennicutt, an astronomer at the University of Arizona, NASA’s Spitzer Space Telescope “has opened up half the universe to us.” Nursery of Stars In the process, it has exposed cosmic birthplaces Stars take shape in clouds of gas and dust, and planets emerge in disks of debris around new stars Early galaxies are also swathed in dust Little visible light gets out, but these objects still emit heat — and infrared radiation “If you only look in visible light at these objects, you don’t even see the tip of the iceberg — you see the tip of the tip of the iceberg,” says Charles Lawrence of the Jet Propulsion Laboratory in Pasadena, California “We look in the infrared because that’s where the photons are.” 935 Art by Bruce Morser/National Geographic Image Collection ● ABOVE: A star exploded 325 years ago, leaving a debris cloud 15 light-years wide called Cassiopeia A This composite image combines data from three space telescopes The Chandra X-Ray Observatory mapped hot gas (blue and green), rich in iron and silicon from the exploded star The Hubble Space Telescope captured wisps of cooler gas (yellow) Spitzer data (red) revealed a shell of dust from interstellar space heated by the blast’s shock wave 936 NASA/JPL/CALTECH/Oliver Krause, University of Arizona Catching those photons, or light particles, meant going into space, because Earth’s atmosphere blocks most infrared Lyman Spitzer, the American astrophysicist for whom the telescope is named, pointed out the advantages of space telescopes back in 1946 Since then, instruments such as the legendary Hubble Space Telescope have proved him right But the Spitzer telescope’s infrared vision is the keenest ever, thanks to a mirror nearly three feet across, sensitive detectors cooled almost to absolute zero, and an orbit far from Earth’s distracting heat eXpeditions! ● RIGHT: Infrared light concentrated by Spitzer’s mirrors falls on detectors chilled close to absolute zero to detect the faint heat of distant objects Ingenious passive cooling technologies — including a solar panel that doubles as a sun shield — help save the liquid helium coolant Three instruments capture and analyze different infrared frequencies: the Infrared Array Camera (RAC), Infrared Spectrograph (IRS), and Multiband Imaging Photometer (MIPS) How and Where Planets Form Already the telescope has gleaned clues about how and where planets form, and even spotted two of them by picking up their infrared glow It is helping astronomers understand how light and radiation from existing stars can trigger the collapse of gas clouds to form new stars And in the far reaches of space, Spitzer is finding young galaxies glowing in the infrared “We’ve made major progress in searching for galaxies at the beginning of the universe,” says Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics “I’m like a child let loose in a toy store.” 937 Bruce Morser/National Geographic Image Collection (A) (C) ● A: A planet in visible light is shown according to an artist’s concept ● B: Spitzer shows an infrared image of a planet ● C: The disk of debris surrounding Vega is at least 20 times the size of our solar system (B) Now You See It Astronomers have detected more than 150 planets around other stars without actually seeing their light But in late 2004, Spitzer captured infrared light from two Jupiter-size planets Both lie so close to their stars that they orbit in three days and are heated to 704°C (1300°F) or more In visible light, each planet is lost in the star’s glare But in the infrared, each emits its own light Key to detecting this infrared glow was the fact that the planets disappear behind their stars on each orbit As astronomers monitored each system with Spitzer, they saw the light dim as the planet vanished, then brighten as it emerged, adding its light to the star’s “We could use the same trick to study light from even smaller planets,” says David Charbonneau of the Harvard-Smithsonian Center for Astrophysics, who led a team that detected light from one planet Unseen planets probably lurk in a disk of debris imaged by Spitzer around the star Vega The disks are made of fine dust, perhaps kicked up by debris from planets shattered by giant collisions 938 (tl)NASA/JPL/CALTECH/Kate Su, University of Arizona, (tr)NASA/JPL/CALTECH, (bl)NASA/JPL/CALTECH/Robert Hurt eXpeditions! ● ABOVE: Dust girdling the Sombrero galaxy is a circle of shadow in a visible-light image ● BELOW: The circle shines when infrared data from Spitzer are added The glow — the result of stars heating the dust — reveals clumpy regions where new stars are forming The bright spot at the galaxy’s center results from a different heat source: a titanic black hole sucking in matter Golden Age of Astrophysics The fun should continue until Spitzer runs out of the liquid helium that helps cool it, in about 2008 Early in the next decade, NASA plans to launch the James Webb Space Telescope, a much larger infrared observatory “This is the golden age of astrophysics,” says Lawrence “A thousand years from now we’ll look back and say that.” eXpeditions activity Research the James Webb Space Telescope Then prepare a presentation about what its location will be in space, special features that distinguish it from previous telescopes, and what astrophysicists expect from the telescope 939 (t)NASA/Space Telescope Science Institute/Hubble Heritage Team, (b)NASA/Space Telescope Science Institute/Hubble Heritage Team and NASA/JPL/CALTECH/Robert Kennicutt, University of Arizona and University of Cambridge ... During the flood they fish, and in the dry season they graze cattle All year round they harvest fruits, cut thatching grass and reeds, and hunt game on these productive lands At Guma, near the top... near the grazing country of the Bié Plateau beneath them, trees not only keep the water in the It was November, and the summer rains were startdelta fresh but also expand the size of their island... Research the status of and plans for conservation on the Colorado Plateau Discuss whether changes in weather have affected the status and plans and how the plans may affect people who depend on the