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The enigma of soil animal species diversity revisited: the role of small-scale heterogeneity.

Nielsen UN, Osler GH, Campbell CD, Neilson R, Burslem DF, van der Wal R - PLoS ONE (2010)

Bottom Line: 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.Our results provide direct evidence for the hypothesis that small-scale heterogeneity in soils increase species richness of intermediate-sized soil fauna.

View Article: PubMed Central - PubMed

Affiliation: The Macaulay Institute, Aberdeen, UK. uffe@nrel.colostate.edu

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 findings: To 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.

Conclusions: Our 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.

Show MeSH
Average species richness (mean ± s.e., n = 8) at 0–3 cm depth found in the heterogeneous treatment for the biotic groups sampled.Both sampling regimes used in the heterogeneous treatment are presented: d3 represents the same depth as sampled in the homogeneous treatment, whereas mix represents pooled samples collected across shallow (3 cm), medium (7.5 cm) and deep (12 cm) organic horizons.
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pone-0011567-g003: Average species richness (mean ± s.e., n = 8) at 0–3 cm depth found in the heterogeneous treatment for the biotic groups sampled.Both sampling regimes used in the heterogeneous treatment are presented: d3 represents the same depth as sampled in the homogeneous treatment, whereas mix represents pooled samples collected across shallow (3 cm), medium (7.5 cm) and deep (12 cm) organic horizons.

Mentions: We expected differences in affinity of various groups of soil biota to organic soil of certain depths due to associated differences in soil moisture (i.e. between deep, medium and shallow organic horizons, with deep horizons being more moist than shallow horizons). Hence, we used another sampling regime to determine if certain species within each group were unique to specific organic horizon depths in the heterogeneous treatment only. We explored whether the species richness of soil fauna and microbial community evenness within the heterogeneous treatment was similar when sampling only one organic horizon thickness (7.5 cm only, i.e. the single depth sample as explained in Fig. 1) compared with sampling multiple organic horizon thicknesses (3, 7.5 and 12 cm combined, i.e. the mixed depth sample) from within the same treatment. If some species would occur only in specific organic horizon thicknesses, then the species richness or evenness should be greater in the mixed depth sample. However, we found no apparent difference between the two sampling regimes in the species richness of mites, collembolans or nematodes (Fig. 3) or in the evenness of the microbial communities. This suggests that heterogeneity allowed the co-existence of more species of oribatid mites, collembolans and nematodes, but that the species were not restricted to specific organic horizon thicknesses.


The enigma of soil animal species diversity revisited: the role of small-scale heterogeneity.

Nielsen UN, Osler GH, Campbell CD, Neilson R, Burslem DF, van der Wal R - PLoS ONE (2010)

Average species richness (mean ± s.e., n = 8) at 0–3 cm depth found in the heterogeneous treatment for the biotic groups sampled.Both sampling regimes used in the heterogeneous treatment are presented: d3 represents the same depth as sampled in the homogeneous treatment, whereas mix represents pooled samples collected across shallow (3 cm), medium (7.5 cm) and deep (12 cm) organic horizons.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2903492&req=5

pone-0011567-g003: Average species richness (mean ± s.e., n = 8) at 0–3 cm depth found in the heterogeneous treatment for the biotic groups sampled.Both sampling regimes used in the heterogeneous treatment are presented: d3 represents the same depth as sampled in the homogeneous treatment, whereas mix represents pooled samples collected across shallow (3 cm), medium (7.5 cm) and deep (12 cm) organic horizons.
Mentions: We expected differences in affinity of various groups of soil biota to organic soil of certain depths due to associated differences in soil moisture (i.e. between deep, medium and shallow organic horizons, with deep horizons being more moist than shallow horizons). Hence, we used another sampling regime to determine if certain species within each group were unique to specific organic horizon depths in the heterogeneous treatment only. We explored whether the species richness of soil fauna and microbial community evenness within the heterogeneous treatment was similar when sampling only one organic horizon thickness (7.5 cm only, i.e. the single depth sample as explained in Fig. 1) compared with sampling multiple organic horizon thicknesses (3, 7.5 and 12 cm combined, i.e. the mixed depth sample) from within the same treatment. If some species would occur only in specific organic horizon thicknesses, then the species richness or evenness should be greater in the mixed depth sample. However, we found no apparent difference between the two sampling regimes in the species richness of mites, collembolans or nematodes (Fig. 3) or in the evenness of the microbial communities. This suggests that heterogeneity allowed the co-existence of more species of oribatid mites, collembolans and nematodes, but that the species were not restricted to specific organic horizon thicknesses.

Bottom Line: 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.Our results provide direct evidence for the hypothesis that small-scale heterogeneity in soils increase species richness of intermediate-sized soil fauna.

View Article: PubMed Central - PubMed

Affiliation: The Macaulay Institute, Aberdeen, UK. uffe@nrel.colostate.edu

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 findings: To 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.

Conclusions: Our 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.

Show MeSH