i'll jump in that discussion, my background, Process Engineer with specialisation in bioprocess.
I have some expertise en cell culture, fermentation process and some other related fields, but these 2 relates to the current topic. our aquariums are like a small bioreactor, you have a bacterial population, a food source (amonia, nitrates,etc.. carbon).
The bacterial population once a tank is established / cycled will adapt to the avaialable nutrient. Once cycled you have all the bugs you want and need, population will fluctate depending of the surrounding envionment (food (carbone, nitrates), and env. conditions (aerobic, anaerobic, Temp, pH, etc) ). In our tank, 1 type of bacteria cannot process amonia nitrites nitrates, typically different types of bacteria will process different type of 'food', that's the principle of cycling a tank, getting all the needed bugs.
It's true that if you don't feed, bactrial population will decrease. If you feed it will increase. But their is a lag time between low population and high population, once the lag phase is passed, bacterial growth is exponentional, it will grow until it's food source becomes the limiting factor, the death rate will match the new cells, that's where you want your aquarium to be. If the food source is depleted the population will decrease, it can happen drasticaly, and you don't want that to happen, dead cell will generate poluent in the water column. Note that the rate limiting factor could be O2 (oxygen) or something else, think about too much food = exponential growth = less oxygen in the system. In a bioreactor, we can control cell growth rate on nutrient or O2 availability, we try to optimize both.
The risk here, if the food source exceed the bacterial capacity to transform amonia and other poluents to their less toxic by-product, an aquarium could face the equivalent of a mini-cycle, build-up of residus,etc by the time the lag phase is passed.
You also don't want a huge load of bacteria to die of starvation, this will release poluent in the water colomn.
It would be preferable to maintain a constant bacterial population and have a stable system.
as an exemple, you have an established aquarium with many fish (constant system or in equilibrium). if you remove your fish (food source = poop) for a prolonge period of time, you should be feeding your system to maintain your bacterial population if you want to reintroduce the fish all at once. if you don't feed, you have the risk of introduciing a lot of waste to process without the proper bacterial population. your system will get back into an equilibrium state, but it can take some time (think about build up, amonia impact on fish,etc).
and bacteria are also a food source for the micro fauna and the ecosystem, another argument to keep system stable.
i don't know if i helped or not, i stated some already known information, but i could relate some of our aquarium reality to my professional 'expertise' just trying to feed the discussion.
