The food chain breaks or the animal is replaced by another animal,if possible.
  Redcat answered 5 years ago If an organism is extinct, it will affect the whole food web. For example, if a rabbit is extinct, the food in which the rabbits feed on (carrots/grass) would grow more and the foxes (the ones who usually eats the rabbits) would steadily decreased as there is no more rabbits. Hence, more foxes are gone leading to an increase in number of animals in which the foxes used to prey on other than rabbits. This animals would than increased more as there is more food (grass) in which the rabbits feeds on. Hence more animals of that species will increased leading to an over population as there is fewer predators.I could actually go on and on as there is no stop to this. I in conclusion, he food web would be unbalanced. Hope I help :)..