cause a shift in the labour supply curve include changes in preferences, availability of alternative opportunities and migration. Changes in preferences - More women choose to work rather than stay at home to look after their children, increasing the supply of labour. Availability of alternative opportunities – The supply of labour depends on the opportunities available in other labour markets. Migration – Another important source of shrifts in the supply curve of labour lies in the movement of workers from on region/country to another. Price elasticity of resource supply The price elasticity of resource supply (PERS) equals the percentage change in the quantity of resource supplied induced by a percent change in price of the resource. Monopolist factor demand If the producer of a good is a monopoly, the factor demand curve is also the MRPL curve. The curve is downward sloping because both the marginal product of labor and marginal revenue fall as output increases. This contrasts with a competitive firm, for which marginal revenue is constant and the downward slope is due solely to the decreasing marginal product of labor. Therefore, the MRPL curve for a monopoly lies below the MRPL for a competitive firm. The implications are that a monopoly or any firm operating under imperfect market conditions will produce less and hire less labor than a perfectly competitive firm at a given price. Monopsony and oligopsony The definition of a monopsony is an economic market structure that comprises a sole purchaser of a particular good or service in the factor market. In comparison to a monopoly, the primary difference between the two market structures lies in the entities they control. A monopoly is a situation in which a single seller dominates the market. A monopsony is a situation in which a single buyer dominates the market. In this situation, a firm sets the market price it will pay for the factor rather than taking it as market-determined, and the amount of the factor to purchase is chosen at the same time subject to the constraint that the price-and-quantity combination is a point on the market's factor supply curve. Furthermore, monopsonists are typically more prevalent in factor markets in comparison to product markets. A monopsonist is an area of concern for factor markets as, a monopsony has the ability to heavily influence the prices and quantity in the factor market, this is due to the firm’s market