Abstract
Background“The enigma of soil animal species diversity” was the title of a popular article by J. M. Anderson published in 1975. In that paper, Anderson provided insights on the great richness of species found in soils, but emphasized that the mechanisms contributing to the high species richness belowground were largely unknown. Yet, exploration of the mechanisms driving species richness has focused, almost exclusively, on above-ground plant and animal communities, and nearly 35 years later we have several new hypotheses but are not much closer to revealing why soils are so rich in species. One persistent but untested hypothesis is that species richness is promoted by small-scale environmental heterogeneity.Methodology/Principal FindingsTo test this hypothesis we manipulated small-scale heterogeneity in soil properties in a one-year field experiment and investigated the impacts on the richness of soil fauna and evenness of the microbial communities. We found that heterogeneity substantially increased the species richness of oribatid mites, collembolans and nematodes, whereas heterogeneity had no direct influence on the evenness of either the fungal, bacterial or archaeal communities or on species richness of the large and mobile mesostigmatid mites. These results suggest that the heterogeneity-species richness relationship is scale dependent.ConclusionsOur results provide direct evidence for the hypothesis that small-scale heterogeneity in soils increase species richness of intermediate-sized soil fauna. The concordance of mechanisms between above and belowground communities suggests that the relationship between environmental heterogeneity and species richness may be a general property of ecological communities.
Highlights
The great diversity of soil faunal communities was recognised many decades ago [1,2]
The concordance of mechanisms between above and belowground communities suggests that the relationship between environmental heterogeneity and species richness may be a general property of ecological communities
We investigated the influence of this heterogeneity on species richness of soil mites, springtails and nematodes, and the evenness of some components of the microbial communities, as these groups represent a large, not exhaustive, part of the soil food web
Summary
The great diversity of soil faunal communities was recognised many decades ago [1,2]. The exploration of the mechanisms underlying observed patterns of species richness has, to a great extent, been limited to above-ground terrestrial and aquatic plant and animal communities [7]. There is increasing evidence for equivalent positive relationships at smaller spatial scales (e.g. within habitats) for plants [12,13,14] and aquatic invertebrates [15,16,17], with some evidence for soil fauna It has been shown, for example, that the diversity of soil mites increases with microhabitat diversity within sites [18,19], and that the species richness of both soil mites and nematodes increases with the complexity and heterogeneity of the litter layer [20,21,22,23,24]. Due to the intricate nature of soils only a few attempts have been made to explain species richness at such spatial scales, and none of these have tested the importance of small-scale heterogeneity directly
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