Deterministic versus stochastic control in ?-diversity, abundance and co-occurrence patterns of a soil nematode assemblage living in a Mediterranean soil

In this paper we studied the determinism-stochasticity trade-off affecting the structure of a soil nematode assemblage. Specifically, in a field experiment that lasted six months, the soil temperature and moisture con-ditions were manipulated in 14 plots. The generic composition of the soil nematode assemblage was explored by estimations of beta-diversity, its turnover and nestedness components and by fitting rank abundance models. Further the associative aspects between the assemblage members and between them and habitat attributes were accounted for by analyzing the niche overlap based on Pearson correlation coefficients. Using variation parti-tioning and null models, we found that the generic diversity of the assemblage was more strongly determined by non-registered lateral experimental factors (stochastic control). By contrast, the deterministic control-less strong than the stochastic counterpart-was exerted both in synchronization with the changes in habitat char-acteristics and/or with a time delay. The network analysis showed that, under favorable habitat conditions in July, September and October, reduced network modularity and enhanced connectivity were favored, which probably led to a niche-based deterministic selection that outperformed stochasticity. Conversely, under changing experimental conditions in August and lower temperature in November and December, stochasticity would be superior to niche identity, leading to enhanced modularity and relatively loose networks.