Biotic interactions as a structuring force in soil communities: evidence from the micro-arthropods of an Antarctic moss model system.

Current meta-community theories postulate that the structure of local communities depends on dispersal, environmental filtering, and biotic interactions. However, disentangling the relative effects of these factors in the field and for diverse assemblages is a major challenge. A solution is to address natural but simple communities (i.e. with low numbers of species in few trophic levels), wherein one of these factors is predominant. Here, we analyse the micro-arthropod community of a moss-turf habitat typical of the Antarctic Peninsula region, and test the widely accepted hypothesis that this system is abiotically driven. In the austral summers 2006/7 and 2007/8, we sampled nearly 80 units of moss from four islands in the Argentine Islands. Using variance partitioning, we quantified the relative contribution of: (1) multiple scale spatio-temporal autocorrelation; (2) environmental effects; (3) the island effect. Little variance (1 %) was accounted for by sources 1 (1 %, significant) and 2 (<1 %, not significant). The island effect significantly accounted for the largest amount of variation (8 %). There was a relatively large effect of spatially structured environmental variation (7 %). Null models demonstrated that species co-occurred less frequently than expected by chance, suggesting the prevalence of negative interactions. Our data support the novel hypothesis that negative biotic interactions are the most important structuring force of this micro-arthropod community. The analysed system is a good proxy for more complex communities in terms of taxonomic composition and the functional groups present. Thus, biotic interaction might be a predominant factor in soil meta-community dynamics.