During perception, the sensory receptors are active and they receive stimulus from their surroundings. However, the complete perception of any stimulus is interpreted by the brain because only brain is capable of differentiating between the sensory stimulus based on the pathway followed by them. On the basis of perceived information, action potential signals are generated that are sent back to the sensory organ (perceiving the stimulus at their end) for further responses.
When wolves were removed from the habitat, the elk thrived, causing a population increase. more elk means an increase in the need for food. The leaves of an aspen tree make good food for elk causing over-grazing and soon, the "aspen trees will be eaten out."
