Open Data

Communities of soil insects in tropical rainforests are among the richest and most complex, but the mechanisms structuring them remain mostly unknown. Identifying whether nutrient availability plays a relevant role in the assembly of these communities poses several challenges due to the diverse nutritional requirements of insects. We investigated the importance of nutrient availability in accounting for the abundance, richness and composition of soil-insect communities in two tropical rainforests. We sampled soil insects 72 one square-meter sampling points across three topographic levels at two sites in French Guiana, counted all specimens and characterized each assemblage using DNA metabarcoding. We then determined the importance of nutrient availability by measuring 19 nutrient concentrations and ratios from pools of litter and topsoil.We collected 18,000 specimens from 17 different orders.Despite an extraordinary diversity and spatial heterogeneity, the concentrations of sodium (Na), potassium (K), magnesium (Mg) and calcium (Ca) positively correlated with either the abundance or the richness of the communities. We found similar relationships when analyzing the data separately for Blattodea, Coleoptera, Hymenoptera and Orthoptera, the most abundant insect orders with the most OTUs. These micronutrients were also important predictors of the composition of the assemblages. We did not find effects for nitrogen or phosphorus, and only the concentration of carbon in the litter strongly influenced the compositions of the hymenopteran and orthopteran communities. This lack of effect indicated that the availability of macronutrients was not a relevant driver of the communities in tropical rainforests as it is for plants and microbes, in contrast to micronutrients.Our results demonstrated that the availability of micronutrients played a large role in species selection during the assembly of the soil-insect communities in these tropical rainforests.The high unexplained variance, however, suggests that additional neutral and niche deterministic processes, such as stochastic population drift and biotic interactions, likely play complementary roles in structuring insect communities in the soils of tropical rainforests.