The relationship between vector species richness and the risk of vector-borne infectious diseases

Infectious diseases can impact human welfare and impede wildlife
management. Much recent research explores whether biodiversity increases
or decreases infectious disease risk. Here we theoretically study the
relationship between vector species richness and the risk of vector-borne
diseases by an epidemiological model of a single host and multiple
vectors. The model considers that vectors are involved in interspecific
feeding interference that causes transmission interference and in
interspecific recruitment competition that mediates susceptible vector
regulation. The model reveals three possible shapes of the vector
richness-disease risk relationship: monotonic amplification, hump-shaped,
and monotonic dilution patterns. Monotonic amplification pattern occurs
across a wide parameter region. Hump-shaped or monotonic dilution patterns
are found when transmission interference is strong and recruitment
competition is weak. Unexpectedly, susceptible vector regulation does not
only promote dilution but can strengthen amplification if coupled with
strong transmission interference. Our results suggest that vector richness
might be more likely to cause amplification rather than dilution, and
shifts in the community mean trait values of vectors could also affect
disease risk along the vector richness gradient.