Survival Of The Mathematical

May 30 2013 @ 2:19pm

One of Derek Thompson’s commenters explains Stephen Jay Gould’s theory about why cicadas emerge on prime-numbered years:

[Gould's] thought was that it dealt with predators having a large production of young every few years. For example, if the cicadas produced every 16 years instead of 17 a bird species producing lots of young every 4 years and smaller broods in the other 3 years would have a bounty for their birds when it intersects with the cicada year. Therefore those that produced heavily every 4 years AND hit the jackpot on the cicadas every 4 cycles could produce enough that year to offset the inefficiency of producing too many in the other 3 years.

But since the cicadas are on a prime number timer this strategy doesn’t work. Producing too many young every 4 years misses the big year that comes on the 17th year as it does the 13th year. Making that a really crappy survival strategy.

Update from a reader:

That theory is not Stephen Jay Gould’s. There is a long history of discussion of the periodical cicadas’ life history going back at least to Darwin. I can’t be sure who suggested it first, but the theory goes back at least to Monte Lloyd and Henry Dybas in 1966.  Gould, as was his custom, was commenting on the work of others in his popular monthly column for Natural History (in fact, Gould credits Lloyd and Dybas in his original column, which makes him, in some respects, a sort of ur-blogger). If you want to get into all things cicadical, look at the website of Chris Simon at the University of Connecticut and click on the left on “Periodical Cicadas”.

Dan Nosowitz describes another fascinating survival strategy – “predator satiation”:

It’s contrary to the survival strategies of almost every other animal: it intends for a huge percentage of its population to be eaten. It doesn’t care. The idea is to overwhelm predators with numbers, since the predators can only eat so many. The only other species that practices predator satiation in the US is the salmon.

[Cole Gilbert, a professor of entomology at Cornell University] estimates that anywhere from 15 to 40 percent of this brood will be eaten, but the density of Brood II is massive. There could be up to 1.5 million cicadas per acre, so even a loss of 40 percent leaves, well, probably still a couple billion cicadas from this brood alone. That said, 1.5 million per acre is very high; many areas won’t have one percent that many. Gilbert estimates that the brood will need between 3,000 and 4,000 cicadas per acre “to swamp the predators.” So each acre will need significantly more cicadas than that to survive to breed in that area again.