The Allee effect in hosts can weaken the dilution effect of host diversity on parasitoid infections

Although numerous studies have shown disease prevalence to be influenced by changes in biodiversity, few studies have explored which factors affect the relationship between biodiversity and disease. When species richness increases, the abundance of host species decreases due to the limited available resources. Low population density may yield a low population growth rate and a high chance of extinction caused by a variety of mechanisms such as mate limitation and inefficient cooperative defense/breeding, i.e. the Allee effect. However, few studies investigating the diversity-disease relationship have taken the Allee effect into account. Here, using a multi-host-parasitoid model, we found that the Allee effect can weaken the host dilution effect, to a degree that depended on the strength of the Allee effect and the aggregation of parasitoid attack. The Allee effect within hosts can protect them from being parasitized and increase the risk of host-parasitoid system collapse. These results may provide an alternative explanation for non-linear relationships between biodiversity and parasitic disease prevalence, and, therefore, can contribute to reconciliation of current disputes over dilution effects.