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equally high speeds in order not to end up as lunch for an even faster animal.
For other, more sedentary animals, speed is less important. Herbivores may
not need to be able to travel quickly to gain a meal, but they might need to
move rapidly in order not to become a meal. Plants are not going anywhere,
at least not very quickly, and so animals that depend on plants for their food
may take their time. Not all animals need to be fast; the fast ones do not need
to be fast all the time. Many of them spend a good deal of their time at rest. It
is only when a predator turns up that they might need to be able to turn on
the speed as and when necessary.
Many predators use speed as a way of hunting their prey, though the
acceleration of a predator is often more important than its top speed to its
success in hunting. The critical factor to the outcome of a hunting chase is
distance between predator and prey at the time the chase commences. If
the predator manages to get close enough to its prey, it will have enough
time to accelerate to a speed that is higher than the prey. If the chase
begins with the predator too far from the prey, the predator will not be
able to sustain its speed to catch it. This is of course if the predator and prey
engage in a straight chase, which is often not the case; swerving and turning
usually contribute to the success or failure of the prey's efforts to escape.
Interestingly enough, very fast animals that depend on high speed to catch a
prey animal often also depend on very slow speeds for their success as they
try to position themselves to close the gap between themselves and their
prey. They do this by stealth, and to be stealthy an animal needs to be slow
and silent.
In very general terms, larger animals are more capable of higher speeds than
smaller ones. There are obvious exceptions, of course; the giant tortoise and
the elephant are two. There are differences, however, some of them great, in
terms of the speed of animals of similar sizes.
Maneuverability
An animal's physiognomy determines how maneuverable it is, which does
not simply make it easier for the animal to get around but rather like speed
maneuverability may be an issue of life or death. Animals often depend on
their maneuverability to escape the clutches of a predator. The ability of the
hunted to swerve sharply at speed is a tactic that compensates for a top
speed that may be slower than that of the hunter. A gazelle might not be
able to outrun a cheetah in a straight race; to elude a predator the gazelle
needs to depend on its maneuverability and the speed with which it can
make these maneuvers. The ability to execute very tight turns at speed
has therefore become an evolutionary imperative for the survival of some
species.
The point in the chase at which an animal executes its evasive maneuver
is critical to its successful escape. If the acceleration of the prey's swerve
