Chapter 9 Summary

Summary

When a mammal or other animal runs, its metabolic rate typically increases linearly with its speed. Metabolic rate and speed are related by a J-shaped power function in swimming fish. For animals engaged in flapping flight, metabolic rate is expected to exhibit a U-shaped relation to speed, but this theoretical expectation is not always observed in real animals.
Cost of transport is the energy cost of covering a unit of distance. The speed that minimizes the cost of transport is the speed that maximizes the distance that can be traveled with a given amount of energy.
Running animals, animals flying by flapping flight, and swimming fish exhibit three distinctive and coherent allometric relations between minimum cost of transport and body weight. For animals of any particular body size, running is the most expensive way to cover distance, flying is intermediate, and swimming by fish is the least expensive. Within any one locomotory group, the minimum weight-specific cost of transport decreases as body size increases.

An animal’s maximum rate of O₂ consumption (V̇_{O_2max}) is significant for two principal reasons. First, it determines the maximum rate at which sustained, aerobic exercise can be performed. Second, it serves as a benchmark by which the strenuousness of submaximal aerobic work can be assessed. Sustained work becomes more strenuous—and more quickly fatiguing—for an individual as it demands a higher proportion of the individual’s V̇_O₂max.
Major phyletic groups sometimes exhibit consistent differences in V̇_O₂max. Among vertebrates—as a rough but important rule of thumb—V̇_{O_2max} in mammals and birds is about an order of magnitude higher than V̇_{O_2max} in fish, amphibians, and nonavian reptiles of similar body size, assuming that the latter groups are at body temperatures near mammalian and avian levels. Within a single phyletic group, V̇_{O_2max} typically tends to vary with body size in an allometric fashion, with small-bodied species having higher V̇_O₂max per gram of body weight than large-bodied species.
Individuals of a species that are similar in age and gender typically vary considerably in V̇_O₂max. Some of this variation can be attributed to differences in training. Usually a significant proportion of the variation can also be attributed to inheritance and/or early developmental effects.