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The cicadas use prime numbers as their emergence period time I thought they mention it in the article. I think that fact is the most fascinating part. >2, 3, 5

The cicadas use prime numbers as their emergence period time I thought they mention it in the article. I think that fact is the most fascinating part. >2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, ... and so on

knowaveragejoe 3y ago
I recall that this has something to do with the ebb and flow of their predator's populations, over the eons it has aligned with periods of declining predator population.
dylan604 3y ago
There are youtube videos that talk about this. Using 2,5,7 while being prime, just didn't offer enough separation to offer the best protection from predators. A smaller prime number allows the possibility that a predator could be around for more than one emergence. Evolutionary pressures found a balance at the 13/17 year gaps to mimimize that from occurring.
- madcaptenor 3y ago
  I've also heard - but don't remember why - that there's some reason why primes of form 4n+1 would be preferred to primes of form 4n-1, which is why you don't see 11-year or 19-year cicadas.
  - dylan604 3y ago
    After further thinking back on this, it wasn't just survival from predators. It also had to do with the sharing of resources with different broods. At 13/17 combos, the overlap seems to balance out that each brood has the resources to continue with low risk of sharing. Every couple hundred years seems to be far enough that the species is not at risk of competition ending one of the broods.
LgWoodenBadger 3y ago
What does it matter whether their cycles are primes when their predators all have cycles of 1?
- weberer 3y ago
  It becomes a problem if broods emerge two years in a row. Then the predator population would not have enough time to die down before the second emergence.
- zem 3y ago
  if predators breed annually, that means that one year is the clock-tick, not the cycle. as a very simplified example, let's say there is some fixed availability of prey. so if there are a ton of predators born and/or come to maturity in one year, they will exhaust the food supply, spend their time and energy fighting for food or starving, and have a population crash next year. the reduced population that year will have a glut of food and a surplus of time and energy for breeding, leading to a boom the year after that, for a two-year cycle with a one-year tick.
data-ottawa 3y ago
Stuff like this is so cool. The golden ratio is really neat too, it works out to the longest period between overlaps for leaves and petals, which maximizes energy per cost. An interesting aspect of that is that phi =1+1/phi, which if you expand that fraction it becomes 1+1/(1+1/(1+1/(...))), so it's actually the irrational number least approximatable by rationals. All repeating rotations are rational ratios, and so phi, being the least appriximable gives the angle with the least overlap for leaves over any number of leaves.

knowaveragejoe 3y ago

I recall that this has something to do with the ebb and flow of their predator's populations, over the eons it has aligned with periods of declining predator population.

dylan604 3y ago

There are youtube videos that talk about this. Using 2,5,7 while being prime, just didn't offer enough separation to offer the best protection from predators. A smaller prime number allows the possibility that a predator could be around for more than one emergence. Evolutionary pressures found a balance at the 13/17 year gaps to mimimize that from occurring.

madcaptenor 3y ago
I've also heard - but don't remember why - that there's some reason why primes of form 4n+1 would be preferred to primes of form 4n-1, which is why you don't see 11-year or 19-year cicadas.
- dylan604 3y ago
  After further thinking back on this, it wasn't just survival from predators. It also had to do with the sharing of resources with different broods. At 13/17 combos, the overlap seems to balance out that each brood has the resources to continue with low risk of sharing. Every couple hundred years seems to be far enough that the species is not at risk of competition ending one of the broods.

LgWoodenBadger 3y ago

What does it matter whether their cycles are primes when their predators all have cycles of 1?

weberer 3y ago
It becomes a problem if broods emerge two years in a row. Then the predator population would not have enough time to die down before the second emergence.
zem 3y ago
if predators breed annually, that means that one year is the clock-tick, not the cycle. as a very simplified example, let's say there is some fixed availability of prey. so if there are a ton of predators born and/or come to maturity in one year, they will exhaust the food supply, spend their time and energy fighting for food or starving, and have a population crash next year. the reduced population that year will have a glut of food and a surplus of time and energy for breeding, leading to a boom the year after that, for a two-year cycle with a one-year tick.

data-ottawa 3y ago

Stuff like this is so cool. The golden ratio is really neat too, it works out to the longest period between overlaps for leaves and petals, which maximizes energy per cost. An interesting aspect of that is that phi =1+1/phi, which if you expand that fraction it becomes 1+1/(1+1/(1+1/(...))), so it's actually the irrational number least approximatable by rationals. All repeating rotations are rational ratios, and so phi, being the least appriximable gives the angle with the least overlap for leaves over any number of leaves.