Hm, Shen, that does not make much sense: if increasing "nrg required for repro" makes bots more fit, then they will outcompete the earlier bots and become more populous. The only exception is if the mutation just appeared and did not have time to spread yet. But then by the next snapshot these bots should dominate.
Actually, there is another exception - speciation. If some bots evolve towards reproducing at lower nrg and having a lot of children and at the same time some bots evolve towards reproducing at higher nrg and having less children, then the "most populous" would be skewed towards the former bots. But that would be a major breakthrough - I don't think anyone ever saw two different species of bots co-exisitng and co-evolving. This would simply blow my mind!