Feeding strategies of soil macrofauna: a microcosm study on assimilation efficiency and litter consumption across 19 tropical species

Detritivorous macrofauna play a key role in litter decomposition through litter consumption and the breakdown of organic matter. Species may differ in the way they influence the decomposition process due to variations in their life history traits creating an important functional diversity which remain poorly explored in tropical ecosystems. Furthermore, most feeding experiments investigating this process are conducted in microcosms without soil. However, this can alter the environment and the availability of nutrients for the fauna, and in turn inducing contrasting responses to the presence of soil challenging the accuracy of consumption rate estimates. We investigate these questions by comparing feeding performances of 19 tropical species, representing four taxonomic classes ( i.e. diplopods, isopods, gastropods and earthworms) through monospecific microcosm experiments, with and without soil, measuring specific litter consumption rate and assimilation efficiency. Without soil, our results show specific litter consumption rate ranging between 7.1 ± 1.0 mg/g/day for the snail Pleurodonte discolor and 383± 79.6 mg/g/day for a woodlice species (Thrichorhina sp). We showed that there was a link between specific litter consumption without soil and macrofauna fresh biomass which is class-specific and strongly dependent on the presence of soil. In addition, detritivorous macrofauna tend to compensate for their consumption by having a higher specific litter consumption when soil was not available questioning methods usually used for estimating this important feeding parameter. On average, assimilation efficiency of gastropods (71%) and isopods (70%) was higher than diplopods (18%), however there was a strong intra-class variability with species having very contrasted feeding strategies within a same class especially for diplopods. Measuring feeding performances for a large number of detritivorous macrofauna allowed us to bring an important brightening on the functional diversity of these species often classified into a single functional group “litter-transformers”.