In addition to having a positive effect on species richness, habitat area can influence the presence of predators, which can indirectly influence prey richness. While these direct and indirect effects of area on richness occur simultaneously, no research has examined how predation might contribute to variation in species-area relationships (SARs). We extend MacArthur and Wilson’s equilibrial theory of island biogeography by including predation-induced shifts in prey extinction, and predict that predators will reduce slopes of prey SARs. We provide support for this with data from two insular ecosystems: (1) orthopteran richness in Ozark glades (rocky herbaceous communities within a forested matrix) with and without insectivorous lizards, and (2) zooplankton richness in freshwater ponds with and without zooplanktivorous fishes. Our results emphasize that anthropogenic activities yield simultaneous changes in processes altering diversity and that it is critical that we understand how these components of anthropogenic change interact to impact diversity.