Environmental Engineering Reference
In-Depth Information
metabolism, making such a low-level homeothermic ef-
fort hardly more useful than heterothermy.
An evolutionary compromise is thus in evidence as
advantages of relatively high and stable body temperature
(near the biochemical optimum) are set against the dan-
gers of heat death, water loss, and the costs of metabo-
lism and insulation (Spotila and Gates 1975). The link
between endothermy and the evolutionary success of
birds and mammals is obvious. Possession of a constant
portable microenvironment required countless feeding
and behavioral adaptations and hence very high meta-
bolic rates, but it conferred competitive advantages in
benign environments and opened up even the most in-
hospitable parts of the biosphere for colonization. Our
species could not have succeeded without it; ectothermic
sapience is unthinkable with life as we know it.
The energetics of animal locomotion has been
surveyed by Pedley (1977), Schmidt-Nielsen (1984),
Videler (1993), Alexander (1999a; 2003), and Biewener
(2003). Here I present only the essentials, first by intro-
ducing cross-modal generalizations and then by focusing
on some of the most remarkable performances in run-
ning, jumping, flying, and swimming. Comparisons of
animal locomotion are done best in terms of the cost of
transport (COT), the quotient of metabolic energy used,
and the product of body mass and distance traveled (J/
kg m). This treatment eliminates speed as a variable
and makes it possible to generalize energy requirements
of unrelated species moving at speeds differing by more
than 1 order of magnitude (fig. 4.4).
4.3 Locomotion
Much of the human fascination with animals arises from
our admiration of flying geese, hovering hummingbirds,
jumping salmons, swimming whales, or running horses.
Many feats of animals in motion (from squirting scallops
to gliding tree snakes) are extraordinary, but none more
so than the annual long-distance migrations (Alerstam,
Hedenstr¨m, and ˚ kesson 2003). Among the famous
accomplishments are the annual 3600-km flight of Mon-
arch butterflies from Canada to Mexico, the 11,500-km
swims of loggerhead turtles from California to Japan,
the up-to-1000-km countercurrent advances of Pacific
salmon in Canadian rivers, and the unrivaled 19,000-
km/a peregrination of the Arctic tern between Green-
land and Antarctica. The modalities of long-distance
animal navigation have yet to be satisfactorily explained
(Alerstam 2006).
4.4 Energy cost of transport. Running is always the most, and
swimming the least, energy-intensive mode of locomotion. Fly-
ing falls in between, but only a few flyers are heavier than 10
kg. Based on Schmidt-Nielsen (1972), Tucker (1975), and T.
M. Williams (1999).
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