Community Assembly Reveals How Environmental Controls Over Rodent Competition Drive Deer Mouse Density and Hantavirus Infection.

Host diversity can strongly influence disease prevalence, but whether it dilutes or amplifies disease remains debated. We applied community assembly theory to examine whether conditionality from abiotic and biotic filtering could explain variation in rodent diversity and Sin Nombre hantavirus (SNV) prevalence across 24 locations in the southwestern United States. Overall, community composition, not diversity per se, drove diversity-disease relationships. Environmental factors determined community composition, which regulated primary host abundance and SNV infection via resource competition. Across roughly half the communities, dilution effects emerged because added species increased dietary overlap, reducing focal host abundance and SNV infection. In other communities, environmental and biotic structuring favoured competitors, suppressing host abundance and SNV infection across diversity levels. Our results highlight how environmental structuring and substitutive assembly processes interact to influence diversity-disease patterns. Community assembly theory provides a framework for integrating abiotic and biotic processes to inform landscape-scale disease patterns.