Data from: When less is more and more is less: the impact of sampling effort on species delineation

Taxonomy is the very first step of most biodiversity studies, but how
confident can we be in the taxonomic-systematic exercise? One may
hypothesise that the more material, the better the taxonomic delineation,
because the more accurate the description of morphological variability. As
rarefaction curves assess the degree of knowledge on taxonomic diversity
through sampling effort, we aim to test the impact of sampling effort on
species delineation by subsampling a given assemblage. To do so, we use an
abundant and morphologically diverse conodont fossil record. Within the
assemblage, we first recognize four well established morphospecies but
about 80% of the specimens share diagnostic characters of these
morphospecies. We quantify these diagnostic characters on the sample using
geometric morphometrics, and assess the number of morphometric groups,
i.e. morphospecies, using ordination and cluster analyses. Then we
gradually subsample the assemblage in two ways (randomly and by mimicking
taxonomist work) and redo the ‘ordination + clustering’ protocol to
appraise the evolution of the number of clusters related to sampling
effort. We observe the number of delineated morphospecies decreasing when
increasing the number of specimens, whatever the subsampling method,
resulting mostly in less morphospecies than expected. Such rather
counter-intuitive influence of sampling effort on species delineation
highlights the complexity of taxonomical work. This indicates that new
morphotaxa should not be erected based on small samples, and encourages
researchers to largely illustrate, measure, and quantitatively compare
their material to better constrain the morphological variability of a
clade, and so to better characterize and delineate morphospecies. --