Parasite richness/sampling effort/host range: the fancy three-piece jigsaw puzzle

In this article, Jean-François Guégan and Clive Kennedy propose an alternative explanation for the confounding effects of host geographical range and sampling effort on parasite species richness using pathway analysis procedure. They suggest that much of the species richness revealed by sampling effort is also a reflection of host range. Thus, the total contribution of host range logically incorporates a contribution from sampling effort. The implications of indirect effects of host range on richness estimates have not previously been discussed, and the authors here attempt to redress the balance. The contribution of host range to richness, as derived from control of sampling effort on richness estimates, therefore, is a mathematical expression that does not take into account the cause-and-effect nature of things.