Estimating terrestrial biodiversity through extrapolation

TLDR

Assessing global biodiversity urgently requires estimation and extrapolation, and future inventories must rely on effective sampling and estimation procedures, especially for hyperdiverse terrestrial groups, with challenges in estimating local species richness and assemblage complementarity across spatial, temporal, and functional scales. The study presents and evaluates multiple estimation methods, introduces a simple complementarity metric with biogeographic examples, and stresses the importance of reference sites for calibrating sampling and assessing true richness and composition. Local richness is estimated by extrapolating species‑accumulation curves, fitting parametric abundance distributions, or applying non‑parametric individual‑based techniques, while a straightforward complementarity measure is proposed to gauge assemblage distinctness. These tools enable rapid, approximate assessment of species richness and faunal or floral composition at comparative sites.

Abstract

Both the magnitude and the urgency of the task of assessing global biodiversity require that we make the most of what we know through the use of estimation and extrapolation. Likewise, future biodiversity inventories need to be designed around the use of effective sampling and estimation procedures, especially for ‘hyperdiverse’ groups of terrestrial organisms, such as arthropods, nematodes, fungi, and microorganisms. The challenge of estimating patterns of species richness from samples can be separated into (i) the problem of estimating local species richness, and (ii) the problem of estimating the distinctness, or complementarity, of species assemblages. These concepts apply on a wide range of spatial, temporal, and functional scales. Local richness can be estimated by extrapolating species accumulation curves, fitting parametric distributions of relative abundance, or using non-parametric techniques based on the distribution of individuals among species or of species among samples. We present several of these methods and examine their effectiveness for an example data set. We present a simple measure of complementarity, with some biogeographic examples, and outline the difficult problem of estimating complementarity from samples. Finally, we discuss the importance of using ‘reference’ sites (or sub-sites) to assess the true richness and composition of species assemblages, to measure ecologically significant ratios between unrelated taxa, to measure taxon/sub-taxon (hierarchical) ratios, and to ‘calibrate’ standardized sampling methods. This information can then be applied to the rapid, approximate assessment of species richness and faunal or floral composition at ‘comparative’ sites.