Body size–density relationships and species diversity in parasitic nematodes: patterns and likely processes

We examined the patterns of body size distribution in parasite nematodes in relation to species diversity and abundance. We hypothesized that parasite body size is optimized and we used the net transmission rate as a fitness function. The net transmission rate was derived from classical epidemiological models. We tested the predicted patterns emerging from the optimal model using observed patterns of nematode distribution and abundance of terrestrial mammals. Our model predicts a value for the slope of the relationship between parasite body size and host body size that is found for the oxyuroids, a highly host-specific group of nematodes with direct life cycles.