Data from: A multivariate test of disease risk reveals conditions leading to disease amplification

Theory predicts that increasing biodiversity will dilute the risk of
infectious diseases under certain conditions and will amplify disease risk
under others. Yet, few empirical studies demonstrate amplification. This
contrast may occur because few studies have considered the multivariate
nature of disease risk, which includes richness and abundance of parasites
with different transmission modes. By combining a multivariate statistical
model developed for biodiversity–ecosystem–multifunctionality with an
extensive field manipulation of host (plant) richness, composition and
resource supply to hosts, we reveal that (i) host richness alone could not
explain most changes in disease risk, and (ii) shifting host composition
allowed disease amplification, depending on parasite transmission mode.
Specifically, as predicted from theory, the effect of host diversity on
parasite abundance differed for microbes (more density-dependent
transmission) and insects (more frequency-dependent transmission). Host
diversity did not influence microbial parasite abundance, but nearly
doubled insect parasite abundance, and this amplification effect was
attributable to variation in host composition. Parasite richness was
reduced by resource addition, but only in species-rich host communities.
Overall, this study demonstrates that multiple drivers, related to both
host community and parasite characteristics, can influence disease risk.
Furthermore, it provides a framework for evaluating multivariate disease
risk in other systems.