Species distribution patterns and the scale of host interactions quantitatively but not qualitatively affect the diversity–disease relationship

Abstract Evidence is accumulating to show that changes in host diversity can affect disease risk, yet the relationship between them is still disputed. Understanding what factors influence this relationship will help to reconcile this debate. In this paper, through spatially-explicit simulations, we investigated the effects of host spatial distribution patterns, the scale of host interactions (i.e. local vs. global interactions), the presence or absence of life history trade-offs, and community assembly rules on the diversity–disease relationship when the pathogen was a generalist. The results showed that intraspecific aggregation enhanced disease risk, while increased global interactions between hosts reduced disease risk. For a given host species richness level, the effect of the scale of host interactions on disease risk increased with intraspecific aggregation. However, neither species distribution patterns nor the scale of host interactions could reverse the diversity-disease relationship. The direction and strength of diversity on disease risk depended on community assembly and life history trade-offs. These results suggest that species distribution patterns and the scale of host interactions do not contribute to the discrepancy in results that lead to the debate over dilution effect, highlighting the complexity of mechanisms underlying the diversity–disease relationship.