You’ve got some of that wrong. The only reason animals don’t use up all of their food source is because other animals further up the chain use them for food. When you remove the predators that feed on deer for example, you end up with an unchecked population of animals that strip everything edible and then some die of starvation.
You’re also attributing human qualities to animals that haven’t yet evolved to where we are mentally.
No humans actually shit in their drinking water. Not sure where you get this. If you have a stream or river moving fast enough than defecating in it is smarter than anywhere near where you may be camped but animals don’t even think that far ahead.
Animals also roam based on the season (like humans used to), they can shit all over an area and by the time they come back it’s become food to eat.
We are on the same page for the bigger picture but you need to work on your argument if you want to be taken seriously.