Optimizing Earthworm Sampling in Ecosystems

To quantify the role of earthworms in ecosystems, a precise and accurate estimation of their diversity, abundance and biomass is needed. In this chapter, we contribute to the optimization of earthworm sampling in terms of (1) how to sample, (2) where to sample and (3) how many samples to take. First, we assess optimal concentrations of chemical expellants (allyl isothiocyanate (AITC) and mustard) recently recommended for earthworm sampling. The efficiency of these vermifuges is then evaluated against formalin application using a combined earthworm sampling method (extraction followed by hand sorting). Practical considerations are discussed. Like many living organisms, earthworm populations are neither uniformly nor randomly distributed, but exhibit an aggregated distribution in patches. The range of spatial autocorrelation in these patches is an important variable to consider in spatial sampling designs. Based on a literature overview, guidelines for spatial sampling design are presented. Finally, species rarefaction curves are used to determine the optimal sample size to accurately represent earthworm diversity.