But the odds are, in that case, that one or both of those populations (or species) will adapt to that conflict by modifying their perception of the niche in a way that lessens the competition. Competition by a rival species is like predation by another species: it is a condition to adapt to, it is not a condition that one "battles" any more than one evolves strategies to combat colder winters or desertification. The natural solution is to adapt: few species have the kind of battle to the death that is characteristic of wars among competing humans.
So in interspecies relations "survival of the fittest" is not the preferred strategy; and in intra-species relations even less so.
A theory of biological evolution based on "the Law of Survival of the Just-Barely-Fit" provides a better explanation of the extinction and evolution of species than that based on "the Law of Survival of the Fittest"; it provides an explanation of the evolution of organisms of increasingly greater complexity, answering the best scientific objection of the Creationists; and it shows that cooperation and creativity are positive factors in human social evolution.
Finally, it can be represented in a mathematical form that can be developed in such a way as to avoid the insertion of ideological constraints.