Spatial microdistribution of mites and organic matter in soils and caves

Spatial variability is a key to understanding the structure and function of soil biodiversity. This research addressed the question of whether a mite centimetric spatial pattern corresponds to that of organic matter in two caves and in the mineral horizon of three forest soils. Therefore, different statistical tools were used and compared: classic aggregation analysis through variance-to-mean ratio and Morisita's index, nested hierarchical ANOVA and Moran's I autocorrelation coefficient. The spatial pattern of organic matter was generally found to be of the gradient or patch type, influenced by slope and trees. Cave sediments far from the entrance contained smaller patches of organic matter than deep soil and cave entrances. Mite density spatial patterns sometimes corresponded to that of organic matter in soils but never in caves. Correlograms of mite species composition were significant in soils but not in caves. The difference between the space available in caves compared with that in the tortuous pores of soil is thought to be a major structuring factor for mites, by influencing their mobility. Correlograms were the most dependable spatial analysis tools, as they could be statistically tested and used to clarify the patterns detected by the nested hierarchical ANOVA method.