Lyme disease, a vector-borne zoonosis, is affected by loss of species by a process known as the dilution effect (7), whereby increasing species diversity decreases disease prevalence by diluting the availability of competent hosts with increased numbers of noncompetent hosts. Little research on the dilution effect has been carried out beyond its effect on Lyme disease (8) , yet the global implications of the phenomenon-if the effects are applicable to other types of diseases and transmission dynamics-could have substantial and enduring effects on human health and conservation.