Performance of species richness estimators across assemblage types and survey parameters

Abstract

Aim A raw count of the species encountered across surveys usually underestimates species richness. Statistical estimators are often less biased. Nonparametric estimators of species richness are widely considered the least biased, but no particular estimator has consistently performed best. This is partly a function of estimators responding differently to assemblage-level factors and survey design parameters. Our objective was to evaluate the performance of raw counts and nonparametric estimators of species richness across various assemblages and with different survey designs.Location We used both simulated and published field data. MethodsWe evaluated the bias, precision and accuracy of raw counts and 13 nonparametric estimators using simulations that systematically varied assemblage characteristics (number of species, species abundance distribution, total number of individuals, spatial configuration of individuals and species detection probability), sampling effort and survey design. Results informed the development of an estimator selection framework that we evaluated with field data.Results When averaged across assemblages, most nonparametric estimators were less negatively biased than a raw count. Estimators based on the similarity of repeated subsets of surveys were most accurate and their accumulation curves appeared to reach asymptotes fastest. Number of species, species abundance distribution and effort had the largest effects on performance, ultimately by affecting the proportion of the species pool contained in a sample. Our estimator selection framework showed promising results when applied to field data.Main conclusions A raw count of the number of species in an area is far from the best estimate of true species richness. Nonparametric estimators are less biased. Newer largely unused, estimators perform better than more well known and longer established counterparts under certain conditions. Given that there is generally a trade-off between bias and precision, we believe that estimator variance, which is often not reported when presenting species richness estimates, should always be included.

Evaluating estimators of species richness: the importance of considering statistical error rates

“…). Because the performance of species richness estimators often increases for less diverse communities (Reese, Wilson & Flather ), we expect our results to represent an optimistic or best‐case scenario that is broadly applicable to many assemblages. The example data set consisted of catch data of fish in 52 Florida lakes between 2006 and 2010 (Bonvechio et al .…”

“…However, many studies have demonstrated that the efficacy of this extrapolation depends on the number of species observed, the shape of the species‐abundance distribution (O'Hara ; Doi & Mori ) and the relative vulnerabilities of species to the sampling method (Brose, Martinez & Williams ; Walther & Moore ; Hortal, Borges & Gaspar ; Beck & Schwanghart ; Reichert et al . ; Reese, Wilson & Flather ). These inconsistencies have resulted in the development of a large number of estimators with unique properties and a plethora of scientific studies seeking the best estimator for particular systems.…”

Spatial richness patterns of soft-bottom fish in the Colombian Caribbean continental shelf and slope

“…The other estimators provided plausible values ranging from an average of 99 (bootstrap) to 265 (Chao) predicted species per spatial unit for an average of 79 observed species per spatial unit. The performance of asymptotic species richness estimators depends on a variety of assemblage attributes (e.g., species abundance distribution, spatial aggregation and species detection probability), sampling design and effort (Reese et al, 2014). Sources of the georeferenced occurrences are heterogeneous, although each were based on bottom trawling, in the sense that they included a diverse array of surveys and cruises with different field designs and spatial and temporal coverage (García and Armenteras, 2015).…”

Biodiversity and Habitat Characteristics of the Bycatch Assemblages in Fish Aggregating Devices (FADs) and School Sets in the Eastern Pacific Ocean

“…Some authors have demonstrated that a raw count of the number of species in an area is far from the best estimate of true species richness (Reese et al, 2014). Despite its wide appeal and apparent simplicity, accurate estimates of species richness can be remarkably difficult to achieve using only the observed number of species.…”