Wild cats need to count calories, too news.sciencemag.org/plants-animals/2014/10/wild-cats-need-count-calories-too A sleek cheetah races with legs outstretched, leaping with a great burst of energy to bring down a fast-moving antelope. That iconic image of this African wild cat needs a footnote. The world’s fastest runner actually spends very little time and energy at full speed, a new study finds. Instead, its most strenuous activity is simply walking around in the hot sun, looking for potential prey (1). Its much the same story for the cheetah’s American cousin, the puma, which spends more than twice as much energy locating prey than researchers had predicted (2). Scientists have long wanted to know how large carnivores spend their days and how many calories they need to survive. Until now, researchers have had only rough estimates of the animals’ total daily energy expenditure. Yet this information is key to managing wildlife, says Terrie Williams, a wildlife physiologist at the University of California (UC), Santa Cruz. For these animals, the bottom line is do you have enough calories to live and to reproduce? That’s been a missing piece of information. Her group and another independent research team have taken some innovative steps to quantify energy use in wild cats. Williams and her colleagues developed a collar that monitors the movement and activity of pumas living in Californias Santa Cruz Mountains, and they calibrated the collar by testing captive pumas on a treadmill. A different team spent weeks tracking cheetahs from dawn to dusk, analyzing the animals feces to determine energy use. As a result, they were able to more finely divide up the day in terms of the different types of activity the animals were engaged in, says John Laundré, a large carnivore ecologist at UC Riverside, who was not involved in either study. Cheetah populations have plummeted in the last century, from about 100,000 in 1900 to about 10,000 today. Some researchers think lions and hyena are in part to blame for the decline. They are able to steal dead prey from the cheetahs, forcing them to spend what seems like an inordinate amount of energy in high-speed chases after more food. To figure out if food theft was really a big problem, Michael Scantlebury, a conservation physiologist at Queens University Belfast in the United Kingdom, and colleagues studied 19 cheetahs in two South African reserves. His team put radio collars on the animals, injected them with water with heavy hydrogen and oxygen atoms so these elements could be traced, recorded the animals behaviors, and collected their feces to check for how fast those atoms were used, an indicator of metabolic rate. We knew exactly where they were, what they were doing, and what they were eating, he says. The cheetahs spent about 3 hours a day walking around—which uses up about 42% of their energy budget. They chase prey less than twice a day, about 38 seconds per sprint, Scantlebury and colleagues report online today in Science. That [time for] energy expenditure is really short, Laundré says. Either they catch them or they give up. And the cheetahs are successful catching prey about half the time. Only four out of 43 times did the cheetahs lose their catch to hyenas or lions—not enough to put a strain on the cheetahs, Scantlebury says. He calculates that even if 25% of the prey were stolen, the cheetahs could compensate by just adding about an hour to the time they spent wandering around. He worries, however, that in an effort to please tourists, game managers will increase the numbers of large predators in reserves, putting the cheetahs at greater risk of having their meals stolen out from under them. He found that cheetahs dont hunt when lions are nearby, or they move away—which could be energetically costly. Also, the data indicate that life would be tough on these animals if prey were scarce or inaccessible because of boundary fences that break up the landscape, forcing the cheetahs to spend a lot more time searching. Williams and UC Santa Cruz ecologist and co-author Christopher Wilmers had long wanted to study the energetics of the local pumas. Unlike cheetahs, which hunt by day in very open landscapes, pumas are active at night in rugged territory and so are hard to watch. To monitor the movements of the cats, Williams and their colleagues developed collars equipped with GPS and devices that measure changes in acceleration and magnetic fields. By analyzing collar data for captive pumas walking or running on a treadmill, pouncing on dead prey, and going through their daily routines in a fenced yard, the researchers learned how to use the collar to figure out an animals activity as well as its location. It gives you information about a very secretive animal, Scantlebury says. The pumas spend about 2 hours a day looking for food. Some wander around quite a bit—and it takes a fair amount of energy for them to traverse the rugged terrain, Williams and her colleagues report online today in Science. Others just sit and wait. Of that time, the actual kill—a powerful pounce that can take down animals larger than the puma itself—takes just seconds in a high energy burst. And the pumas moderate the power of the bounce depending on the size of the prey, the researchers discovered. Ultimately the animals are using strategy to keep the [energy] cost as low as possible, Williams says. However, their results indicate that she and others have underestimated by 2.5 times what it costs these animals to make a kill. And wildlife managers should take heed. If we’re going to have carnivores in a system we’ve got to provide what they need to live, she adds. Those provisions should include not just enough prey, but the right landscape for capturing that prey, Laundré says. In that terrain, predators will expend less energy. “The better they are able to balance their energy needs, the better they will do. Video: Wild cats need to count calories, too video.sciencemag.org/News/3817875203001/1 A sleek cheetah races with legs outstretched, leaping with a great burst of energy to bring down a fast-moving antelope. That iconic image of this African wild cat needs a footnote. The world’s fastest runner actually spends very little time and energy at full speed, a new study finds. Instead, its most strenuous activity is simply walking around in the hot sun, looking for potential prey. Its much the same story for the cheetah’s American cousin, the puma, which spends more than twice as much energy locating prey than researchers had predicted. References 1. Flexible energetics of cheetah hunting strategies provide resistance against kleptoparasitism Science 3 October 2014: Vol. 346 no. 6205 pp. 79-81 DOI: 10.1126/science.1256424 sciencemag.org/content/346/6205/79 Editors Summary The costs and benefits of stalking and chasing Organisms live under a constant balance between getting and using energy. Large carnivores may feel this balance more acutely because of the large amounts of energy needed to capture and subdue their prey. Williams et al. and Scantlebury et al. used remote measures of physiology and behavior to identify the hunting strategies of the stalking North American puma and the speedy African cheetah (see the Perspective by Laundré). In both cases the cats hunting strategies are well matched to produce a balance between the energy they spend on the hunt and the energy they acquire from their prey, despite their very different strategies and levels of competition. Science, this issue p. 81 (2), p. 79 (1); see also p. 33 (3) Abstract Population viability is driven by individual survival, which in turn depends on individuals balancing energy budgets. As carnivores may function close to maximum sustained power outputs, decreased food availability or increased activity may render some populations energetically vulnerable. Prey theft may compromise energetic budgets of mesopredators, such as cheetahs and wild dogs, which are susceptible to competition from larger carnivores. We show that daily energy expenditure (DEE) of cheetahs was similar to size-based predictions and positively related to distance traveled. Theft at 25% only requires cheetahs to hunt for an extra 1.1 hour per day, increasing DEE by just 12%. Therefore, not all mesopredators are energetically constrained by direct competition. Other factors that increase DEE, such as those that increase travel, may be more important for population viability. Supplementary Materials sciencemag.org/content/suppl/2014/10/01/346.6205.79.DC1/Scantlebury.SM.pdf 2. Instantaneous energetics of puma kills reveal advantage of felid sneak attacks Science 3 October 2014: Vol. 346 no. 6205 pp. 81-85 DOI: 10.1126/science.1254885 sciencemag.org/content/346/6205/81 Editors Summary The costs and benefits of stalking and chasing Organisms live under a constant balance between getting and using energy. Large carnivores may feel this balance more acutely because of the large amounts of energy needed to capture and subdue their prey. Williams et al. and Scantlebury et al. used remote measures of physiology and behavior to identify the hunting strategies of the stalking North American puma and the speedy African cheetah (see the Perspective by Laundré). In both cases the cats hunting strategies are well matched to produce a balance between the energy they spend on the hunt and the energy they acquire from their prey, despite their very different strategies and levels of competition. Science, this issue p. 81 (2), p. 79 (1); see also p. 33 (3) Abstract Pumas (Puma concolor) live in diverse, often rugged, complex habitats. The energy they expend for hunting must account for this complexity but is difficult to measure for this and other large, cryptic carnivores. We developed and deployed a physiological SMART (species movement, acceleration, and radio tracking) collar that used accelerometry to continuously monitor energetics, movements, and behavior of free-ranging pumas. This felid species displayed marked individuality in predatory activities, ranging from low-cost sit-and-wait behaviors to constant movements with energetic costs averaging 2.3 times those predicted for running mammals. Pumas reduce these costs by remaining cryptic and precisely matching maximum pouncing force (overall dynamic body acceleration = 5.3 to 16.1g) to prey size. Such instantaneous energetics help to explain why most felids stalk and pounce, and their analysis represents a powerful approach for accurately forecasting resource demands required for survival by large, mobile predators. Supplementary Materials sciencemag.org/content/suppl/2014/10/01/346.6205.81.DC1/Williams.SM.pdf 3. How large predators manage the cost of hunting Science 3 October 2014: Vol. 346 no. 6205 pp. 33-34 DOI: 10.1126/science.1260170 sciencemag.org/content/346/6205/33 Being a large carnivore is not easy. First, there is the food, the energy they need to survive, which by definition consists mainly of other animals. This means that meeting daily energetic needs is not as easy as just going out and gathering plants that are waiting around to be found and eaten. Large carnivores often prey on animals that are bigger than themselves and that try to avoid being killed. Foraging by carnivores becomes a two-player game of stealth and fear (1), making it more difficult and thus energetically costly for carnivores to catch enough to stay alive. Large carnivores must balance the energy spent seeking and subduing prey with the energy they get back when they catch something—which does not happen as often as one might think (2–4). Two reports in this issue, by Scantlebury et al. (5) on page 79 and by Williams et al. (6) on page 81, look at how two carnivores, cheetahs (Acinonyx jubatus; see the first photo) and pumas (Puma concolor; see the second photo), tread the fine line of energy losses and gains in order to survive. Photo: (a) For cheetahs, walking around in a hot landscape costs more energy than chasing down prey. (b) The hunt is on. Cheetahs reach famously high speeds during hunting, but Scantlebury et al. show that it is the search for prey rather than the chase itself that is energetically more costly (Figure 1 of 10.1126/science.1260170). (c) Stealthy hunter. Pumas hunt by stalking and ambushing their prey. Williams et al. show that—as in the case of the cheetah—seeking prey is more energetically costly than subduing the prey.
Posted on: Sun, 05 Oct 2014 10:14:08 +0000
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