Some carnivores move to search for and capture prey, while others sit and wait

Many carnivores forage throughout their habitat, moving about in search of prey. Examples of species that hunt in this way include wolves, sharks, and hawks. Other carnivores remain in one place and attack prey that move within striking distance (as do moray eels and some snakes, such as mambas and vipers) or enter a trap (such as a spider's web or the modified leaf of a carnivorous plant).

Many carnivores have unusual physical features that help them capture prey. The body form of the cheetah, for example, enables great bursts of speed that allow it to catch gazelles and other rapidly fleeing prey. In another example, most snakes can swallow prey that are considerably larger than their heads (FIGURE 12.8). Unlike those of other terrestrial vertebrates, the bones of a snake's skull are not rigidly attached to one another. This unique feature allows the snake to open its jaws to a seemingly impossible extent. Curved teeth mounted on bones that can move inward then help to pull prey items down the throat. A person with similar adaptations would be able to swallow a watermelon whole.

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FIGURE 12.8 How Snakes Swallow Prey Larger Than Their Heads (A)Snakeshave movable skull bones that allow them to swallow surprisingly large prey. (B) This golden tree snake (Chrysopelea ornate) eating a butterfly lizard larger than its head. View larger image

While some carnivores depend primarily on their physical structure, others subdue prey with poison (e.g., venomous spiders). Still others use mimicry: ambush bugs, scorpionfishes, and many other predators blend into their environment so well that prey may be unaware of their presence until it is too late. Some predators have inducible traits that improve their ability to feed on specific prey species. The predatory ciliate protist Lembadion bullinum has such an inducible offense: individuals gradually adjust their size to match the size of the available prey.

The garter snake (Thamnophis sirtalis) is the only predator known to eat the toxic rough-skinned newt (Taricha granulosa). In some of its populations, the skin of this newt contains large amounts of tetrodotoxin (TTX), an extremely potent neurotoxin. TTX binds to sodium channels in nerve and muscle tissue, thus preventing nerve signal transmission and causing paralysis and death. A single newt can contain enough TTX to kill 25,000 mice—far more than enough to kill a person, as was tragically demonstrated in 1979 when a 29-year-old man died after eating a rough-skinned newt on a dare.

The garter snakes in some populations, however, can eat rough-skinned newts because they can tolerate TTX. These snakes have TTX-resistant sodium channels (Geffeney et al. 2005). Although these garter snakes are protected from the lethal effects of TTX, those individuals that can tolerate the highest concentrations of TTX move more slowly than less resistant individuals—a trade-off between tolerance for the poison and speed of locomotion. In addition, once they swallow a poisonous newt, the snakes are immobilized for up to 7 hours. During that time, the snakes are vulnerable to predation themselves and may also suffer from heat stress.