Change in the Demand Environment

Complements: This shows that if the price of peanut butter goes up and people keep buying it, the price of bread will also go up. This is because peanut butter and bread are complements of each other. One is bought because of the other. If you have peanut butter, you usually eat it on bread so if you buy peanut butter then you must also buy bread. Because of this, if the price and demand of one goes up, then the price and demand of the other will also go up.

Substitute: This shows the decrease in the brand name cereal. You can substitute the brand name cereal for the store brand cereal. You get the same thing for lesser price therefor making the demand of the brand name product go down. Because you a substituting one product for another, you are taking away demand from the original product giving its demand graph a decreasing look.