A new paper has just come out:
Rohde, K. and Rohde, P.P. (2008). How to measure ecological host specificity. Vie et Milieu-Life and Environment 58 (2), 121-124.
It deals with the following problem: most parasites infect more than one host species, nectar feeding birds, as well as bees and other insects, usually visit more than one plant species, etc. Nevertheless, they often have preferences for particular “host” species. How do we measure this? Obviously, just counting the host species is unsatisfactory, because this would ignore such preferences. Our index considers not just the number of hosts, but the intensity and frequency of their use as well.