Ask any baker what organism drives their sourdough starter and they will say Saccharomyces cerevisiae — brewer's yeast, the same species that makes beer and bread. It is the most studied microorganism in human food history.
It is not the dominant yeast in sourdough starters. Across all flour types (all-purpose, bread, whole wheat) and all feeding schedules tested, the yeast genus Kazachstania rapidly became the most abundant fungus. Not Saccharomyces. The organism most bakers assume drives their starter is a minority player.
The bacterial communities responded to flour type as expected — different Lactobacillus species dominated different flours. Flour choice shapes the bacterial side of the fermentation. But the fungal community converged to the same endpoint regardless of input. Kazachstania dominated every starter, on every flour, on every feeding schedule.
This asymmetry is the finding. The factor bakers can control — flour selection — governs the secondary microbial community (bacteria, which produce acid and flavor). The dominant organism (the yeast that produces CO₂ and drives the rise) is governed by constraints the baker cannot see or change. The input you choose determines the flavor but not the leavening. The substrate affects only the workers you didn't hire.
In complex ecosystems, the variable you control may govern only the secondary players. The dominant organism finds its own way, indifferent to the substrate, governed by competitive dynamics invisible from outside the jar.