Blackwell Publishing

Natural selection and variation - What is the struggle for existence?


Why does this excess fecundity exist?

The condition of 'excess' fecundity - females produce more offspring than survive - is universal in nature. In every species, more eggs are produced than can survive to the adult stage. The cod dramatizes the point in one way, because its fecundity, and mortality, are so high; but the same point is true for species which have lower reproductive rates. Darwin once famously calculated that even the slow breeding elephant (pictured opposite) produces far more offspring than could ever hope to reach maturity.

This excess fecundity exists because there are inadequate resources in nature to support all the eggs that are laid and all the young that are born. There are only limited amounts of food and space in the world; a population can expand but there will come a point beyond which the food supply must limit its further expansion. Thus members of a population, and members of different species, compete in order to survive, and this follows from the conditions of limited resources and excess fecundity.

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