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Supporting Information
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Appendix S1. Wind tunnel description and methodological issues
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We used a newly built wind tunnel at Stockholm University (Fig. S1). Wind was created by a
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radial fan connected to the wind tunnel. To avoid vibrations caused by the fan motor, the fan and
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the tunnel itself were placed on two separate tables (without direct contact), and the connection
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between the fan and the tunnel was flexible. To reduce the background levels of particles in the
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tunnel we filtered the inflowing air to the fan using NSB/290 (class G4) filters (Camfil, Trosa,
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Sweden). However, when increasing the filtering capacity the maximum possible wind speed
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decreased. To reach wind speeds of 4.3 m/s we could therefore not completely remove the
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background level of particles (Fig. 1). Therefore, the method may be less suitable for species
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with few spores, as the spores released from such species may be difficult to separate from the
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background level of particles. We attached the sporophyte and started the experiments at 0.8 m/s
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(instead of 0 m/s) for two reasons. First, starting the fan created an initial wind gust that was
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somewhat higher than the desired wind speed, which potentially could affect spore release.
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Second, the initial background level of particles caused by spore release during attachment of the
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studied capsule in the tunnel was reduced more quickly when starting the experiment at a low
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wind speed. To create a laminar air flow through the experimental chamber in the tunnel, the air
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went through a package of thin pipes (plastic straws), ’airflow straighteners’, covering the whole
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opening (Fig. S1). In experiments with turbulence we added a frame (Fig. S1) with horizontal
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threaded rods across the tunnel (experiments with laminar air flow were performed with an
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empty frame).
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Fig. S1. The wind tunnel with (a) a transparent window, (b) an isokinetic probe (inflow diameter
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70 mm) attached to a (c) particle counter for detecting spore release, (d) a hotwire anemometer
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for measuring wind speed, (e) a sporophyte attached to (f) a crocodile clamp, (g) a frame with
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five horizontal rods across the tunnel for creating turbulence, (h) a package of pipes (5 mm in
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diameter) for creating laminar wind flow, (i) an outflow of the fan that is connected to the tunnel,
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(j) a radial fan, and (k) filters for the inflow air. The wind tunnel was painted black inside and
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was illuminated by a LED lamp attached to its ceiling. Scale in centimeters.
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Table S1. Prior distributions (all uninformative) and final estimates of model parameters
Parameter
Description
Prior distribution
Parameter estimate:
mode (95% credible interval)
β1
Wind speed
N(0,.001)†
-1.00 (-1.44 – -0.54)
β2
High turbulence
N(0,.001)
-0.95 (-1.37 – -0.54)
β3
(Wind speed)2
N(0,.001)
0.15 (0.06 – 0.24)
β4
Interaction term
N(0,.001)
0.78 (0.62 – 0.92)
τ1
Precision of log(particle)
Ga(.001,.001)‡
2.79 (2.26-3.38)
Φ
Random intercept
N(0,.001)
0.99 (0.45– 1.52)
τ2
Precision of intercept
Ga(.001,.001)
19.0 (3.65-221.4)
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† N(a,b) signifies a normal distribution with mean a and precision b.
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‡ Ga(a,b) signifies a gamma distribution with scale a and shape b.
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