Wednesday, May 21, 2014

"Infant" Mortality

I've been teaching ecology to 9th- and 10th-graders lately.  While watching a video segment that featured young arctic fox cubs that depended for their survival on their mother's ability to bring home equally-cute snow goose chicks for dinner, I pointed out that, over the long term, both foxes and geese were likely to raise only about two offspring per couple to maturity over their whole lives.  That's the simple consequence of having a stable population: parents can only replace themselves--nothing else will serve.  Of course, that is the overall average over a whole population, over a long enough period to even out variations in resources, etc.  Even so, it is instructive to meditate upon: there are always more young born than can survive. 

In light of this fact, the overwhelming fecundity of trees is even more incredible.  Walking the dogs a few days ago, I found myself looking at a tiny bit of the vast untimely death that is a normal part of life.

Immature Norway maple fruits on sidewalk.

These winged fruits (called "keys') each contain two embryos.  They are only a fraction of the size they normally reach at maturity, so could not survive even if they had landed in a better spot.  Although it has been a bit gusty lately, I'm pretty sure they were aborted, rather than simply blown down.  I can't say why; their loss must represent a significant waste of resources for the tree. 

The only good I can see from such an event is that the tree's loss is inevitably someone else's gain; insects, worms, fungi and the like small creatures will feast on the keys for some time.  And, of course, natural selection could not perfect the Norway Maple Way of Life without the competition for existence that results from too many young competing for a chance at survival.

Don't worry--there're plenty more.

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