Inter-annual Variations of True Species Richness in a Subtropical Butterfly Assemblage: An Estimation Based on Least-biased Extrapolations of Species Accumulation Curves

More or less strong inter-annual variations of species richness are well known in insects in general and in butterfly in particular. Yet, such variations generally rely upon more or less partial samplings and are rarely reliably documented in relevant terms of “true” total species richness (instead of “simply” observed number of species). In addition, equity of sampling completeness between annual inventories proves hard to ensure in practice and had long remained difficult to check properly. Thus, as neither standardized sampling procedures nor rarefaction procedure at a same sampling size may reliably warrant the equity of sampling completeness, asymptotic estimations of total species richness should imperatively be implemented for each annual inventory. This implies that, among the different estimators of the number of missing species available in the literature, the least-biased one should be adequately selected at first, for each annual inventory. As such a procedure of selection is now made available, it becomes possible to tackle relevantly the issue presented above. Applying this procedure to the field data recorded (and already published) by Lee et al. for butterfly assemblages at Mount Gariwang-san (south Korea), surveyed during several years, I show that (i) “true” inter-annual variations of species richness may indeed vary in a large range - from simple to double - along successive years; (ii) annual total species richness represents only a limited part - comprised between less than ≈ 40% and at most ≈ 80% - of the potential species richness of the site (i.e. the true species richness along several years pooled together) .