Can yeasts eat other yeasts?

No yeast doesn't eat other yeast. Yeast eats sugar, glucose to be specific. If there is no glucose around but there are other sugars, starches or alcohols, yeast creates machines (enzymes) to convert these into glucose. The yeast carries information in its DNA for dozens of machines specific to many food sources.

Flour has a lot of starch in it, which is made of long chains of sugar molecules. Flour carries its own enzymes that work on the starches and chop them into simple sugars. This happens after the flour has been rehydrated with water or other liquids. Then the yeast uses the sugars for energy.

Yeast is a one-celled microorganism growing all around us and on us. It grows when it has food and water, and suspends growth when it does not. In suspended animation, it is light enough to be blown by the wind, like a seed. If there is water and food where it lands, it will reproduce and continue the cycle.

Yeast eats sugar, glucose to be specific. If there is no glucose around but there are other sugars, starches or alcohols, yeast creates machines (enzymes) to convert these into glucose. The yeast carries information in its DNA for dozens of machines specific to many food sources.