Allometric estimation of earthworm ash-free dry mass from diameters and lengths of select megascolecid and lumbricid species

Abstract

We present novel length to ash-free dry mass and preclitellar diameter to ash-free dry mass allometric equations for seven earthworm species from the families Megascolecidae and Lumbricidae, all of which are exotic and most of which are of ecological concern in North America: Eisenia hortensis, Eisenia fetida, Dendrodrilus rubidus, Lumbricus rubellus, Octolasion sp., Amynthas hilgendorfi, and Perionyx excavatus. We also present a length–biomass allometric equation for one enchytraeid, Mesenchytraeus sp. All relationships between length and biomass, and diameter and biomass were statistically significant at the species and family level (P<0.001). The predictive powers of these allometric regressions (as coefficients of determination, r2) were species-specific, and ranged widely from 0.27 to 0.93. Length–biomass regressions provided more predictive power and precision overall than preclitellar diameter–biomass calculations at both the species and the family levels. An ANCOVA followed by orthogonal contrasts determined that, while the slopes of these regressions did not differ significantly between the two earthworm families, significant differences in slopes of length–biomass regressions existed among species within families, indicating the utility of having species-level equations for accurate biomass predictions. With these allometric relationships, we aim to improve the estimation of earthworm biomass in order to facilitate investigations of how exotic-invasive earthworm species impact soil ecosystems.