Terra incognita of soil biodiversity: unseen invasions under our feet

Whilst cartographers of the 19th century endeavoured to chart the last unknown lands, the great challenge for biologists in the 21st century is to fill the gaps on the biodiversity map of the Earth. And one of the largest gaps concerns the biodiversity of soils, a terra incognita right under our feet. The study of soil biodiversity, and particularly the complex communities of small invertebrates, has suffered from a severe ‘taxonomic impediment’ (Decaëns [Decaëns T, 2010]) leading to great uncertainties about total species richness, phylogenetic diversity, geographical structure, temporal dynamics of soil organisms, and consequently about their role on ecosystem function (Bardgett & van der Putten [Bardgett RD, 2014]). However, the revolution in high‐throughput sequencing is now revealing the hidden biodiversity of the soil with unprecedented detail (e.g. Arribas et al . [Arribas P, 2016]). In a noteworthy from the Cover article in this issue of Molecular Ecology, Cicconardi et al . ([Cicconardi F, 2017]) apply these new tools to study soil communities of Collembola in three distant oceanic islands of volcanic origin, obtaining a striking result: only 38 of 70 species (54%) are exclusively found in a single island, with the remaining shared among islands or with other distant regions, suggesting a massive recent introduction of soil species, whose impact is entirely unknown.