When reasonably stop sampling? How to estimate the gain in newly recorded species according to the degree of supplementary sampling effort.

9 pagesInternational audienceAim: Register new species gradually becomes more difficult as sampling of a communityprogresses, addressing increasingly rarer species. Thus, although biodiversity assessments wouldideally require complete samplings, only partial samplings are ordinarily achieved when speciesabundances distributions are highly heterogeneous within communities, which is often the case.Then, in the frequent context of partial samplings, answering knowingly whether to continue or stopan ongoing inventory require to tentatively assess the “profitability” of the extra sampling effort. Thatis, trying to estimate the number of species expected to be newly recorded thanks to a given furtherincrease of the sampling size.Methods: Such estimate may be conveniently derived on the basis of the recorded numbers f1, f2,f3, fx, of species already recorded once, twice, three, … x-times within the ongoing sampling. Thederivation involves a Taylor expansion of the species accumulation curve, with the successivederivatives of the species accumulation curve being respectively expressed in terms of thesuccessive recorded values of fx.Results: A simple nonparametric estimator of the expected number of newly recorded species isderived as a function of the foreseen additive sampling effort. Depending only upon the directlyrecorded values of the fx within the ongoing sampling, this estimator is easy-to-implement and, inparticular, does not require recording explicitly the species accumulation curve.Conclusion: The practical interest of this estimator is to offer a convenient way to gauge theadditional sampling effort required for a given increase in sample completeness, thus providingquantitative elements to determine whether further continuing an ongoing sampling looksappropriate or not, in the context of both limited available time expenditure and possible othercompeting priorities