If we discount those cicadas with life cycles of ten years or fewer (as being too close to predator life cycles), we find that the most successful emergence rates for cyber cicadas are thirteen and seventeen years-precisely what we find in the wild. They found exactly what Gould had suggested: cicadas with a prime-numbered life cycle had the most successful evolutionary strategy. To test this hypothesis, researchers from Brazil’s Universidade Estadual de Campinas used a computer simulation, very similar to John Conway’s Game of Life, in which simulated cicadas and predators battled it out in a hundred-by-hundred-cell matrix. In Gould’s example, a cicada that emerges every seventeen years and has a predator with a five-year life cycle will only face a peak predator population once every eighty-five (5 x 17) years, giving it an enormous advantage over less well-adapted cicadas. Cicadas that emerge at prime-numbered year intervals, like the seventeen-year Brood II set to swarm the East Coast, would find themselves relatively immune to predator population cycles, since it is mathematically unlikely for a short-cycled predator to exist on the same cycle. Prime numbers, however, can only be divided by themselves and one they cannot be evenly divided into smaller integers. By this reasoning, any cicada with a development span that is easily divisible by the smaller numbers of a predator’s population cycle is vulnerable. Since most predators have a two-to-ten-year population cycle, the twelve-year cicadas would be a feast for any predator with a two-, three-, four-, or six-year cycle. Gould, in his essay “Of Bamboo, Cicadas, and the Economy of Adam Smith,” these kind of boom-and-bust population cycles can be devastating to creatures with a long development phase. According to the paleontologist Stephen J. Now, imagine an animal that emerges every twelve years, like a cicada. The subsequent decline in hares can lead to a drop in the swollen predator population fewer predators can then result in more hares surviving to reproduce and the cycle begins again.
Meanwhile, predators like lynxes and raptors celebrate the hare bubble by gorging themselves and reproducing like mad. That still left an unanswered question: What was behind the rise and fall of the hare populations? A recent hypothesis is that the population of hares rises and falls due to a mixture of population pressure and predation: when hares overpopulate their environment, the population becomes stressed-the fact that the food supply is gobbled up certainly doesn’t help-which can lead to decreased reproduction, resulting in a drop in next year’s hare count.
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