When we last left our population of anaerobic friends, we had the beginning population (Anae1) and two offspring of the same individual (Anae1#101). Anae2#1 had an additional mutation that deactivated one enzyme, but was not phenotypically different from the parent population, and Anae3#1 had an additional mutation that affected two enzymes, and thus its phenotype, by reducing the efficiency and rate at which energy is generated.

So these clones of Anae1#101 will also reproduce, though at different rates, and at the same time, the parent population is still reproducing. For simplification, let's say thateach anae1 member reproduces twice per day, so anae2 will also reproduce twice, but anae3 only reproduces once. So over time, anae1 and anae2 eclipse anae3 in terms of numbers, and it can't compete. The scenario can take a number of different directions depending on the circumstances, all of which fall into natural selection:

Scenario 1: Anae3 is overwhelmed by the other populations. Due to limited space or resources, the scant numbers of Anae3 die off before they can reproduce to keep up the numbers, but the other populations are capable of making up for losses. Anae3 disappears.

Scenario 2: Scenario 1 plus additional phenotypic mutations in anae3 offspring (anae4) that allow the individual to more efficiently reproduce.

Scenario 3: Anae1 and anae2 reproduce too quickly, using up local resources, and die off, whereas slow replicating anae3  doesn't require as fast a turnover of resources and survives.

Scenario 4: Scenario 3 plus phenotypic changes in one or both of the offspring of the  populations (anae5 and anae6) that reduce their reproduction time. Allowing them to survive as well.

Another possibility is

Scenario 5: Survival of all three lineages by spread to other ocean vents for resources.

 In scenarios 2, 4, and 5 we have three populations genetically, but the phenotypes are the same. These are still the same species. It is going to take more changes to evolve.

Let's take a mixture of these scenarios as we proceed. Let's say that not only do the original populations move to separate environments and survive (with their left behind predecessors dying out at the original vent due to a sudden lack of resources - for simplicity), but they've resulted in new phenotypic changes. So we have vent 1 with anae1 (including anae1#101 genetic offspring) and anae 5; vent 2 with anae2 and anae6; and vent 3 with anae 3 and anae4.

Anae4 is the result of anae3#101 engulfing another microorganism and using the energy it produces to reproduce more efficiently (because of integration of the genomes, this characteristic is passed on).

Anae5 is what would've been anae1#564 but it has a mutation in a gene that determines the color of the outer membrane layer of the organism. It is now visible to small fish who like the taste of anae.

Anae6 is anae2#101 with a mutation in the other enzyme (similar to anae 3, but at a different point in the gene)

So...which vent do we want to follow first?