How does species diversity high and low have consequences on

Solution

The higher the species diversity, the diversity of the pathogens would also increase, therefore, pathogen infection per individual would decrease. High species diversity , brings along with itself the dilution effect. The dilution effect hypothesis states that biodiversity which is generally measured by species richness, or the number of different species present in a particular spatially defined locality — is protective against infection with zoonotic pathogens (i.e., pathogens transmitted to humans through animal reservoirs).
It is known that not all the organisms are equally competent hosts for all kinds of pathogens infecting a species. With greater biodiversity, comes a greater number of incompetent hosts for a particular pathogen, thus reducing the chances of infection transmission from one species to the other, as they might be incompetent hosts for that particular pathogen which fails to infect them. A classic example of species diversity and pathogen infection could be seen in the US where Lyme disease, a vector borne disease, gave path to the theory of dilution effect and incompetence of hosts for a particular vector.