DENSITY, BODY-MASS AND PARASITE SPECIES RICHNESS OF TERRESTRIAL MAMMALS

We investigated the relationships between helminth species richness an d body mass and density of terrestrial mammals. Cross-species analysis and the phylogenetically independent contrast method produced differe nt results. A non-phylogenetic approach (cross-species comparisons) le d to the conclusion that parasite richness is linked to host body size . However, an analysis using phylogenetically independent contrasts sh owed no relationship between host body size and parasite richness. Con versely, a non-phylogenetic approach generated a negative relationship between parasite richness and host density, whereas the independent c ontrast method showed the opposite trend - that is, parasite richness is positively correlated with host density. From an evolutionary persp ective, our results suggest that opportunities for parasite colonizati on depend more closely on how many hosts are available in a given area than on how large the hosts are. From an epidemiological point of vie w, our results confirm theoretical models which assume that host densi ty is linked to the opportunity of a parasite to invade a population o f hosts. Our findings also suggest that parasitism may be a cost assoc iated with host density. Finally, we provide some support for the non- linear allometry between density and mammal body mass (Silva and Downi ng, 1995), and explain why host density and host body mass do not rela te equally to parasite species richness.