Wednesday, October 11, 2006

Survival physiology: a reassessment of why big, fierce animals are rare

Tuesday 10 October 2006

Physiologists can provide critical information, such as dietary needs, to help efforts to preserve big, fierce animals. Why are lions and tigers and bears rare, oh my? The answer at its most simple is that big, fierce predators on land and sea expend a lot of energy so they must eat a lot, said Terrie Williams of the University of California at Santa Cruz. Williams, who studies the physiology of large predators and wrote "Hunter's Breath" about her seal research, will speak today at the American Physiological Society conference in Virginia Beach "Comparative Physiology 2006: Integrating Diversity" on the scarcity of big, fierce animals. To fully understand the physiological limits on populations of carnivores weighing 50 pounds or more, scientists need to know more about the food they consume, why and how they eat and the environmental consequences of their feeding, Williams said recently in an interview. Talk abstract is available afterwards ->

She said physiology's critical role in species preservation has been underplayed. "We focus so much on the molecular and the genetic that we've forgotten to pay attention to the basic needs." Physiologists can assist in conservation efforts by defining the energy needs of the large mammalian predators, which is "absolutely critical in how we think about conservation." Such information would improve efforts to conserve environments, preserve vulnerable or endangered species and reintroduce predators to areas they once roamed, she said.

"A lot of the focus [is on] . . . saving habitat," Williams said, "with not that much thought about the large, rare animals that we're now starting to find out form the glue that hold these ecosystems together." Without the large predators, ecosystems can collapse. Williams points to the Pacific sea otter population, which usually feed on the fish found in kelp forests. With the recent rapid decline in otters, which she and colleagues attribute to hungry killer whales, sea urchins have taken over, stripping the marine forests. "And you end up with essentially a desert of urchins looking for something to eat," Williams said.

She also points to the decline of the wolf on the East Coast. "With the absence of those animals, you end up with an overrun deer population, interactions with mice and Lyme disease being a huge, huge problem." The reintroduction of large predators can throw a spotlight on the issue of prey and predators when the animals come into conflict with humans. Williams says the recent reintroduction of wolves in the Yellowstone area was an example of where knowing more about the animals' physiology could have helped scientists address the issue of the wolves' subsequent attacks on domestic animals on the region's ranches.

Canids -- the wolves, coyotes, wild dogs -- eat about twice as much as researchers had predicted. Wild canids are highly aerobic animals compared to domestic dogs, she said. "You have to account for that if you're going to" attempt reintroduction. "Whatever energy you're expending, it's going to cost you in food every single day. As you try to reintroduce large predators, do you double how much [food] they need? How do you account for that?" Williams has turned her focus from marine mammals to terrestrial predators. She recently conducted a pilot study using GPS to track feeding coyotes (she found that even wild coyotes like to eat at city dumps) in hopes of studying jaguars in Peru.


Terrie Williams

Ecology and Evolutionary Biology, UCSC, Center for Ocean Health, 100 Shaffer Road, Santa Cruz, CA, 95060.

In 1978 ecologist Paul Colinvaux posed the question, why are big fierce animals rare, and concluded that both body mass and energetic demands were contributing factors. Using these basic parameters, we have examined the role of energetics in the survival of large (> 21 kg) marine and terrestrial mammals. In general, living in aquatic habitats amplifies both resting and active costs such that the energetic requirements of marine mammals are approximately two times higher than those of terrestrial carnivores. Total active energetic cost, defined as field metabolic rate (FMR), increases allometrically for carnivorous mammals and is described by, FMRterrestrial = 777.7mass0.77 for terrestrial species and FMRmarine = 1367.7mass0.76 for marine species where FMR is in and body mass is in kg. A consequence of these relationships is that large carnivores place extraordinary pressure on prey resources. This is evident in human-predator conflicts involving canids and felids, and in the impact of one of the largest marine carnivores, the 3000 kg killer whale, on marine mammal populations in the North Pacific. Since the 1970s the rate of these population declines as well as other animal extinctions have increased markedly. It is likely that bioenergetic processes underlie many of these events, and could be used to mitigate the loss of species through an improved understanding of the basic physiological requirements of big, fierce animals including humans. survival-physiology-a-reassessment-of-why-big-fierce-animals-are-rare

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