A new index of interactivity in parasite communities.

A new index of interactivity which allows objective evaluation and comparison of interactivity in communities between different host species is presented. The index is derived from the equations for species-accumulation curves generated using non-linear regression (with the Levenberg-Marquardt algorithm) of sample infracommunity richness data. It is advantageous in that it requires only presence/absence data to calculate, is applicable to all parasite taxa (including asexual species), is largely independent of sample size and allows objective comparison of parasite communities while correcting for differences in total richness. Iterative randomisation of infracommunity richness values to generate a mean value for the index avoids spurious results which may be generated by heterogeneity in infracommunity richness and the variation this produces in the non-linear regression results.