HOST DENSITIES AS DETERMINANTS OF ABUNDANCE IN PARASITE COMMUNITIES

Several epidemiological models predict a positive relationship between host population density and abundance of directly transmitted macropa rasites. Here, we generalize these, and test the prediction by a compa rative study. We used data on communities of gastrointestinal strongyl id nematodes from 19 mammalian species, representing examination of 66 70 individual hosts. We studied both the average abundance of all stro ngylid nematodes within a host species, and the two components of abun dance, prevalence and intensity. The effects of host body weight, diet , fecundity and age at maturity and parasite body size were controlled for directly, and the phylogenetically independent contrast method wa s used to control for confounding factors more generally. Host populat ion density and average parasite abundance were strongly positively co rrelated within mammalian taxa, and across all species when the effect s of host body weight were controlled for. Controlling for other varia bles did not change this. Even when looking at single parasite species occurring in several host species, abundance was highest in the host species with the highest population density. Prevalence and intensity showed similar patterns. These patterns provide the first macroecologi cal evidence consistent with the prediction that transmission rates de pend on host population density in natural parasite communities.