Easiest way to separate an ale from a lager: temperature you leave the liquid during fermentation. Lagers, you need to keep much cooler during fermentation than ales. That's why most new brewers do ales, because they don't own the necessary equipment to keep the fermenter at a constant, cold temp
Never heard anything about the yeast being in different locations. I've made a lager by adding yeast to to the top before. The yeast is specialized to be "lager" yeast where it works best under the colder conditions than the yeast you use for ales. The yeast does mix in together throughout the liquid, eating sugars everywhere.
The yeast does multiply as it eats, thats the nature of yeast as a "creature". We often do this on purpose before even adding to our beer. We make a small amount of non descript beer a day before brew day. Add the yeast the same day, let it sit for a day... The yeast multiply and multiply. This is called a starter. We add this as our yeast once our beer is brewed