A system of two noncompeting prey species and one predator is studied, and a graphical method to determine the equilibrium densities of the populations is presented. The method is used to study the behavior of two different systems: with nonterritorial and territorial (self-regulated) predators respectively. It is shown that the introduction of an alternative prey reduces the equilibrium density of the first prey if the predator is not territorial. This is an example of apparent competition. If the predator is self-regulated, then the introduction of an alternative prey may, under some conditions, lead to an increased equilibrium density of the first prey population: apparent mutualism.