CASE 7 PREDATOR–PREY: A GAME OF LIFE AND DEATH

We just saw that metabolic rate increases with activity level. A by-product of metabolism is the generation of heat, which is a necessary consequence of the second law of thermodynamics (Chapters 1 and 6). Animals have several mechanisms for dissipating excess heat, including sweating, changes in blood flow, and (in dogs, for example) panting.

Cheetahs, as top predators, are one of the fastest land animals, capable of speeds up to 70 mph (114 km/h). Such extreme speed generates a lot of heat. Interestingly, instead of releasing the excess heat as it builds up, the cheetah stores it, dissipating it only after a chase.

The amount of heat that cheetahs store during a sprint can be considerable, on the order of 60 times the heat produced at rest. Heat storage raises the cheetah’s body temperature. Cheetahs can therefore reach remarkable speeds but can sustain them only for short durations and must rest for long periods of time between sprints. Because their bodies can support only so much heat storage, cheetahs do not run when the temperature of their environment reaches approximately 105°F (41°C). In other words, the amount of time a cheetah runs and the distance it covers are limited by its body temperature.

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Gazelles, common prey of cheetahs, have similar heat storage mechanisms and are similarly known for their speed and agility. Goats, by contrast, do not store heat as they increase their activity levels, instead dissipating it through evaporative mechanisms. But goats are not known for their speed. Heat storage therefore seems to enable quick bursts of speed, and has evolved as an adaptation among both predators and prey to achieve short, rapid sprints.