It has not reached carrying Capacity
No. Natural selection is the non-random survival of randomly varying replicators. The random variation part could be thought of as mutation and recombination that the non-randompart, natural selection, works with.
Well, all natural processes have an element of chance, of course. But natural selection, deterministic as it is, is much less random than, for instance, genetic mutation. Which is why we generally distinguish between the randomness of genetic variation and the non-randomness of the filtering process that is natural selection.
What population? Perhaps you mean if there were no variation for natural selection to select from.
Genetic variation. If there were no variation in the genes/phenotype then natural selection would have nothing to select from.
How it changes in response to its environment.
That would be the Stabilizing Selection where there will me not a lot of genetic variation. The curve of the population allele frequency would be quite thin with the extreme being in the middle.
Evolution is simply genetic change within a poulation. That change can occur in several ways. One is immigration/emigration: individuals moving in or out of a population bring in or take out their alleles with them. Another is genetic drift, or chance events which cause the frequencies of alleles in a population to fluctuate. New mutations can change the allelic frequency as well. Finally, natural selection can cause some alleles to become more common at the expense of others. In short, natural selection is one of several mechanisms that can bring about evolution.
What population? Perhaps you mean if there were no variation for natural selection to select from.
The population has not yet reached the carrying capacity.-apex :D
There is no need for it to occur. Only if the environment changes and less food is found would there be a change. The environment selects the birds that do the best under the new conditions and the others will die.
What would there be to select from if all the organisms in a population were not different in morphology and behavior. Some of these differences are reproductively successful against the immediate environment, and that environment is the natural selector.
Neither. Lamarckian evolution does not take place at all; almost all of his concepts are now known to be incorrect. The population will still undergo mutation, and natural selection for beneficial mutations and against harmful ones will still occur.
What would be selected if organisms did not have differences that lead to better survival and reproduction, or the opposite. That is all natural selection is.
Genetic variation. If there were no variation in the genes/phenotype then natural selection would have nothing to select from.
There would be no adaptive change due to natural selection and only genetic drift due to random events and gene flow due to population mixing would occur. Alleles would change, but without reproductive variation speciation could not occur.
How it changes in response to its environment.
This would occur when organisms showing many genetic differences caused by mutations and genetic recombination reproduce in a changing environment.
Evolution, of course. Evolution can happen without natural selection in some cases; drift, flow. Generally though, natural selection causes evolution and then, by definition, would come first.
Without variation it would not be selecting, just random death of identical units.