-variation due to a range of representative forms, as stated. Varying ability to deal with the environment. That's one of the key parts of the theory.
If A and B aren't co-evolving, but competing for the same set of resources, sure.
- are you still talking about species A here? Or do you mean a "different kind of" B, that competes better than any other A or B..?
OK, but competition between species and between members of the same species has been covered way back in the start of this thread. So this organism, this B species, gets a mutation that gives it an advantage? Does it get the advantage by having the gene or does it get the advantage by expressing the gene?
Obviously, when it uses the thing -just like a screwdriver or a chisel, say. Another word for screwdriver is "tool".
Does expressing a gene have purpose? Does the organism care what happens?
Genes are tools, that get used. Now someone tell me organisms don't do this, and that using a tool isn't adapting a tool.
By now you should have some idea why people like me suggest you read up on the subject. You have been given an explanation but you have not understood, just as I suggested.You are asking to be spoon fed, If your present question is answered, you will come back with another and so on ad infinitum. All because you cannot be bothered to do a bit of work on the subject yourself.
If you had read up on evolution and got stuck at some point and explained your problem, I would gladly have helped you.