Often in nature, the life cycles of predators and prey sustain each other. If too-efficient predators would wipe out all the prey, the next generation of predators may starve. If too-wily prey effectively evade predators, then the prey may overpopulate or overcrowd their habitat and die of diseases or from lack of food. Often nature assists predators and prey to achieve a rough balance that sustains both populations and their habitats.
This great blue heron, for instance, is a ruthlessly efficient predator who utterly outmatches the 7-for-a-dollar goldfish in my backyard pond. I've watched it catch a fish a minute.
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I've read many accounts of folks who've had their entire goldfish or koi pond population utterly wiped out by herons.
The goldfish's best defense is its fecundity; a female fish may bear 500 young a year. However, she eats most of them herself.
The goldfish in my ponds typically cluster on the very surface where they get fed. Most of them seem to stay there 24/7, just in case food arrives.
And if the heron arrives instead, it has easy pickings. Thus the fish rarely grow more than about 2-3 inches long.
But random changes in critter behavior often drives evolution. Sometimes odd traits are better adapted to longevity or breeding prowess.
And in the goldfish's case, sometimes the rare trait of extra caution produces fish that lurk below and don't crowd the water's surface, eager for food. Those fish may not eat as much, but they survive for extended periods. This fish is over 6 inches long and probably has dodged herons, frogs, raccoons, skunks, cat and other predators for two or three years.
The great cycle of life, and whims of fate and evolution gifted this wily fish with a little extra patience, unlike its eager, and doomed brothers and sisters. It have survived for years now, and may be responsible for hundreds of offspring that support this goldfish population. Someday it will be a danged hearty meal for the heron, but for the moment it is a breathtaking swirl of black and gold in the tannin-stained pond waters.
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