Tautology in evolution and ecology

A popular tautology is that presented by Volterra's model of competition (Volterra and d'Ancona 1935). It assumes that two popUlations grow in a limited system such that, eventually, increase in one population produces a decline of the other. These conditions are presented as constants in the LotkaVolterra equations, from which a strictly mathematical logic shows that two results may be obtained: one population or the other disappears. Because the argument is logically derived from the assumptions, it is tautological. Nevertheless, the argument has received considerable attention, possibly because the conclusions, which are evident in a verbal statement, are more difficult for us to see in the mathematical form