Comparing the richness of engineered and unengineered patches is not sufficient to determine the overall effect of the engineer on species richness at the landscape scale. Changes in richness at the patch scale can have important consequences for the evenness of the distribution of species across the landscape. However, the effect of the engineer on richness at the landscape scale will be negligible unless there are species found in engineered patches that are not found elsewhere in the landscape. Collins and Uno (1983) found that species richness was lower inside buffalo wallows than in the surrounding prairie. However, since buffalo wallows form ephemeral wetlands and thus contain an assemblage of species different from those found just outside the wallows, the authors suggest that the presence of buffalo wallows increases the species richness of the prairie. Thus, even in systems where engineered patches have lower species richness than non-engineered patches, the existence of species uniquely present in the engineered patches will result in ecosystem engineering having a positive effect on richness at the larger scale.