Why should species be ecologically restricted? Why doesn't one omni-talented species evolve and put all the others out of business? When we can answer that question, we will clearly know the explanation of the habitat pattern. We shall know why we see more diversity in places with a greater variety of physical and chemical conditions. But, it turns out, we will also be well on our way to understanding most other diversity patterns too.

The seeds of our answer lie in the very mechanisms of speciation. None of the mechanisms, however, will help without the basic assumption of evolutionary ecology, the tradeoff principle. So, I begin there.

The tradeoff principle

Suppose one single phenotype – call it the super-hero phenotype – could do everything better than any other. Natural selection would discover it and promote it. All other phenotypes would disappear. Only one homogeneous super-hero species would remain.

The tradeoff principle asserts that a super-hero species does not exist and has never existed. (I omit saying ‘will never exist’ because I fear that the onslaught of the human species against all others has not finished.) It says that phenotypes excel at most functions by losing the ability to perform other functions well.