ecography ecog-02461 · edaphic properties enable facilitative and competitive interactions...
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Ecography ECOG-02461Cramer, M. D., Barger, N. N. and Tschinkel, W. R. 2016. Edaphic properties enable facilitative and competitive interactions resulting in fairy circle formation. – Ecography doi: 10.1111/ecog.02461
Supplementary material
1
Supplementary material
Cramer, M.D., Barger, N.N. and Tschinkel, W.R. 20XX. Edaphic properties enable facilitative
and competitive interactions resulting in fairy circle formation. – Ecography 000: 000–000.
Appendix 1
Figure A1 Hypothetical relationship between feedback strengths in fairy circles in a shorter-
grass matrix.
Figure A2 Aerial image image showing fairy circles with hand-drawn polygons around each.
Figure A3 Proportion of the soil volume comprising different particle sizes between sites used
for infiltration measurements.
Table A1 Comparison of the proportion of the soil volume (%) comprising different particle
fractions between sites used for infiltration measurements.
Figure A4 Variation in water infiltration rates with soil texture (proportion of sand, silt and clay).
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Figure A1. Hypothetical relationship between positive (+) and negative (-) feedback strengths (y-
axis, blue line) portrayed in the context of fairy circles (FC) in a shorter-grass matrix. The
nominal range over which positive and negative feedbacks operate is shown. Peripheral grasses
between fairy circle and matrix are shown to be larger than those in the matrix. Blue arrows
indicate possible resources fluxes (i.e. water and nutrients) in the soil. The average distance
between fairy circle peripheries at our study site is shown for reference. Peripheral grasses are
shown to have short-range positive feedbacks due to focussing of resources and longer-range
negative feedbacks due to competitive resource depletion.
Feed
backstrength
+
-
Short-rangeposi5vefeedback
Long-rangenega5vefeedback
FC Matrix FC
5.7m
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Figure A2. A Google earth image showing fairy circles (24.9638°S, 15.9735°E) with hand-
drawn polygons around each. A vehicle track through the site that is more than a decade old has
not eliminated fairy circles that it intersects. Faint game tracks are also visible.
50m
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Figure A3. Comparison of the proportion of the soil volume (%) comprising different particle
sizes (log scale) between sites used for infiltration measurements (Fig. 1) that either had fairy
circles (FC) present or in which there were no fairy circles present (No FC) within 75 m of the
soil sampling point. The grey ribbons represent the 95% confidence bands.
0
2
4
6
-1 0 1 2 3Particle size (Log, μm)
Volu
me
(% p
er s
ize
clas
s)
FCNo FC
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Table A1 Comparison of the proportion of the soil volume (%) comprising different particle
sizes (upper limit of each class in µm: clay <4, silt <62, very fine sand <125, fine sand <250,
medium sand <500, coarse sand <1000, very coarse sand <2000) between sites used for
infiltration measurements (Fig. 1) that either had fairy circles (FC) present or in which there were
no fairy circles present (No FC) within 75 m of the soil sampling point. The P values were
determined using Student’s t- tests (n = 35).
Component No FC FC P
Clay 4.7 ± 1.3 2.4 ± 0.3 0.015
Silt 12 ± 2 7.1 ± 0.6 0.016
Sand 84 ± 4 90 ± 1 0.014
Very fine sand 22 ± 2 19 ± 1 0.248
Fine sand 32 ± 5 30 ± 2 0.603
Medium sand 20 ± 2 22 ± 1 0.329
Coarse sand 9 ± 3 17 ± 2 0.116
Very coarse sand 0.3±0.2 2.9±0.6 0.079
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Figure A4. Variation in water infiltration rates, represented by the colour of the points, with soil
texture (proportion of sand, silt and clay). The blue line represents the linear model for variation
in texture with the 95% confidence interval shown by the grey ribbon. The size of the points
indicates the variation in fairy circle perimeter lengths from the absence of fairy circles (0 m) to
a maximum average of 29 m per fairy circle in a site.
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7580859095100
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Clay
(%)
Sand (%)
Silt (%)
Clay
Sand Silt
FC perimeter (m)●
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0102030
500100015002000
Infiltration rate (mm h−1)