 After constructing their model, E. O. Wilson and his graduate student Daniel Simberloff tested the model by devising natural experiments in the Florida keys (Simberloff &amp; Wilson 1970). They had islands defaunated of varying sizes and distances from the mainland. They could then evaluate the predictions and assumptions of the model. They determined that species abundances returned to their previous equilibria and species richness on an island appeared to be determined by the size of the island and its distance from the mainland. However, Simberloff was able to show that the equilibrium model predicted that the species turnover rate was much higher than what was measured (Simberloff 1976). In some ways, it is not a surprise that the model was predictively inaccurate since it was highly idealized. MacArthur and Wilson had assumed distance alone determines the immigration rate and size alone determines the extinction rate. MacArthur and Wilson wrote,