Elephant fish love call:
It is generally assumed that new species develop when an ecological niche, say an unexploited food source becomes available.  The situation now appears to be more complex.  (Communication and Speciation Manuel Leal and Jonathan B. Losos NATURE vol. 467 no. 7312 September 9, 2010 page 159) 

I confess that when I am thinking about it, my reasoning often starts with, “Suppose a new food source becomes available.”  The science of thermodynamics is so well developed and so secure that – life involving energy flow – one tends to think that energy flow, for which you can read food source, is all that life is about.

I should be the last to fall into such a trap.  Life is also about maintaining a population of suitable size, not too big and not too small.  And this acceptable size range is independent of food source. 

Lo and behold, work has run ahead of me.  The elephant fish of Africa (Amegard, M.E. et al. Am. Nat. 176, 335-356 (2010)) generates an electrical field.  And it can use this field to communicate.  Other animals cannot read the signal, so it is a safe channel to use for mate selection.  Thus armed with privileged communication, the elephant fish have undergone a burst of speciation that is not accounted for by their feeding routines.

Once it has been pointed out, it seems perfectly obvious.  I would hate, however, on the basis of this case alone to try to persuade somebody that this proves that animals must limit their population size.  As we say in radiology, “Consistent with but not diagnostic of …”  

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