Situations where factors of production can be used to produce different goods so that an increase in the supply of one commodity requires a reduction in the supply of another commodity.
Below is a diagram to illustrate this in a supply and demand framework. In this instance farmers use their land to rear animals to produce products such as beef and lamb. However if farmers decide to use more land to rear cows to help produce more beef this causes the supply of beef to increase. However, as land is required to rear other animals such as land, if there is less land available to rear sheep then the supply of lamb will fall. This is all caused because of scarce supply of land.