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COPYRIGHT 2003 Natural History Magazine, Inc.
A small lizard, caught in the open, flushes ahead of a pursuing monitor. The prey, desperately seeking escape, begins to run a winding course. The tactic could throw a predator off, but the monitor doesn't bite. Rather than engage in a tail chase, the monitor heads straight for a pile of rocks--the only nearby feature to which the hunted animal could possibly escape. The smaller lizard, outsmarted, arrives at the refuge too late.
Such a display of intelligence in monitor lizards, the animals of the family Varanidae, is not unusual. As a rule, monitors do not have to chase their prey very far, and in many cases they seem to anticipate some gambit by their prey. When arboreal lizards are being hunted and run for a tree, they usually spiral around to the back side to ascend; one of us (Sweet) has watched pursuing monitors of two species (Varanus tristis and V. glauerti), on at least three occasions, spiral around the tree in the opposite direction to catch the prey unawares. (Experienced human lizard-catchers do the same thing.)
The black-palmed rock monitor (V. glebopalma), a three-foot-long lizard from northern Australia, hunts by taking up perches on three- to six-foot-high boulders along the margins of ledges, where it has a good view of some area of more-or-less open ground. If it spots prey--such as, in Sweet's observations, a skink or a frog--it literally projects itself off the boulder, dashes after the prey, and then returns with its quarry at top speed to some rock crevice before doing anything like chomping or whacking the prey and gulping it down. "Lizards" don't do this: if they have something in their mouth, they eat it then and there--no matter that something else may be zooming in at top speed in hopes of a double lunch. But monitors do.
Predators and their prey are locked into a co-evolutionary arms race, in which any advantage gained by one calls for a countermeasure by the other. Less sophisticated, or perhaps just unlucky, prey individuals perish. On average, those with better means of escape survive. More effective escape, in turn, favors predators better able to capture evasive prey, and the bar for both species rises in a reciprocating fashion. Similarly, competing lineages of predators--cats and foxes, for example--are also subject to the Red Queen's dictum that "it takes all the running you can do, to keep in the same place."
A common result of such pressures--less adept animals either don't catch a meal or can't avoid being eaten--is the evolution of larger brains and more sophisticated nervous systems, as well as a potential for increased intelligence. A successful carnivore might have better neuromuscular coordination than its peers or its prey; more refined senses (and brain to process the information); or enhanced problem-solving capabilities. Those aspects of neurophysiology co-evolve in turn with ecological and behavioral differences among various kinds of carnivores....
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