Preprint Article Version 1 This version is not peer-reviewed

Soil Arthropods Indicate the Range of Plant-facilitation on the Soil of Mediterranean Drylands

Version 1 : Received: 27 February 2020 / Approved: 28 February 2020 / Online: 28 February 2020 (12:20:37 CET)

How to cite: Meloni, F.; Martinez, A.S. Soil Arthropods Indicate the Range of Plant-facilitation on the Soil of Mediterranean Drylands. Preprints 2020, 2020020429 (doi: 10.20944/preprints202002.0429.v1). Meloni, F.; Martinez, A.S. Soil Arthropods Indicate the Range of Plant-facilitation on the Soil of Mediterranean Drylands. Preprints 2020, 2020020429 (doi: 10.20944/preprints202002.0429.v1).

Abstract

Drylands are arid and semiarid ecosystems, where the lack of rains imposes harsh conditions for the survival of organisms. These ecosystems are also susceptible to degradation and desertification, and their conservation depends on the understanding of the ecological functioning of vegetation and soil. In drylands, the vegetation is spatially structured as a mosaic of patches (vegetation) and interpatches (bare soil), a consequence of plant-plant interactions (facilitation and competition). Empirical data and modeling approaches reinforce the role of ecological facilitation for the maintenance of all organisms in drylands. However, the actual range of facilitation is still poorly known. Here, we explored data of meso- and micro-arthropods found in soil as bioindicators to infer the range of facilitation provided by plants to soil. We regarded data of abundances and species densities (independent samples) collected in random patches and bare soil places as dependent variables. Data of patch size and distances between bare soil and patches were arranged in a single shuffle, producing a 1-d coordinate system centered at the border of the patch. Discrete portions of this system are taken to calculate averages and variances of abundance and species density, and we investigated how soil communities variate across the patch border. We employ techniques of signal analysis to reduce the data noise and obtain a smooth and continuous behavior, which allowed us to fit a logistic function. Our findings indicate that soil communities suddenly change from simple patterns to numerous and diverse communities in bare soil regions, meaning that the influence of vegetation on soil goes beyond the patch border. We interpreted the variations in fauna as a consequence of the positive influence provided by plants (or its lack) on surrounding bare soil. We observe a fast decaying of fauna quantities at 0.35 m outside the patch border, a threshold that reveals the mean range of facilitation provided by plants. However, the changes in soil communities outside the patches seem not necessarily related to the efficiency of soil processes mediated by arthropods, which seem to be more active inside large patches. Concluding, we found a minimum patch-size (radius ~ 0.5 m) able to maintain high diverse communities in soil, and an average distance of vegetation influence along the patch border (halo between 0.35 and 0.50 m). This information can be interpreted in terms of facilitation provided by plants to soil conditions, which seems to differ from the quantitative functionality of soil processes. Our findings contribute to the general understanding of the ecological functioning of drylands, as well as to better plan conservation actions.

Subject Areas

ground arthropods; spatial ecology; drylands; logistic function; biological diversity; ecological functioning; threshold values; desertification; conservation.

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