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UDPviper t1_iw8q8al wrote

Reply to comment by PlaidBastard in Are there any K-Strategists insects? by [deleted]

I saw a vid of sea horses where it stated only 1-2% of around 1000 or so births per father survive to adulthood. Brutal odds.

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mabolle t1_iwhzend wrote

You can actually do this math for any species at all, without knowing anything about its biology except how many offspring they tend to have.

Think of it this way: animal and plant populations may fluctuate wildly from year to year, but in the medium-term, we can assume that the per-year average total population of a species is more or less stable — neither increasing or decreasing. This necessarily means that (assuming equal sex ratios, which most species have) each female is having, on average, two offspring per year that survive long enough to have their own offspring. That's one offspring per female to replace herself, and one to replace her male partner. Some females will have much more than two offspring survive to adulthood, and some will have none, but the per-female average is approximately two.

So if you find out that a species tends to have approximately 1000 offspring, you can divide 2 by 1000 to get the survival rate. If the typical litter size is four, you know that only half of them on average will make it. If a species tends to have a million offspring, it's two in a million.

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