The spectacular success of their descendants illustrates the remarkable power of natural selection. According to a new study comparing the athletic abilities of different types of animals, modern marine mammals are so well adapted to aquatic life that they are as efficient in swimming as specialized land mammals are in running. Terrie Williams, an associate professor of biology at UCSC, found that elite animal athletes, from horses to killer whales, achieve an optimal efficiency for locomotion that is determined more by their basic mammalian physiology than by their mode of transportation. In an article published this month in the Philosophical Transactions of the Royal Society of London, Biology, Williams presented a comprehensive analysis of the energetic costs of locomotion in terrestrial, aquatic, and semiaquatic mammals. Her findings indicate that for specialized mammals, whether they run across the plains, swim through the oceans, or fly across the evening sky, the energetic cost of moving through the environment is about the same.
Energy requirements do vary with an animal's size due to metabolic factors.
A swimming grey whale, for example, expends less energy per pound than a bottlenose dolphin. But Williams was surprised to find that the relationship between body mass and energy use is the same for mammals that run, swim, and fly, whereas mammals, fish, and birds show distinct differences. Williams analyzed physiological data from a wide variety of animals, drawing on her own research for some animals, such as dolphins, and on published data for others. The trick is the chassis has to be adapted to the environment, and that means specializing. Semiaquatic animals that try to have it both ways, like muskrats and mink, pay a high price for their versatility, sacrificing energetic efficiency for the ability to move back and forth between land and water.