1.) Organisms are producers when they can make their own food.
2.) If one species in the food web ceases to exist, one or more members in the rest of the chain could cease to exist too. Such as plants, if they didn't give off oxygen and all plants/ trees didn't exists humans would go extinct because we need air to survive.
3.) They would be affected due to the changes that are happening within the city. (I'm not sure on this one)