Supplementary Materials

Trophic cascading effects of avian predation on a willow in an urban wetland

Pei-Chen Wu, Pei-Jen Lee Shaner

National Taiwan Normal University, Department of Life Science, No. 88, Sec. 4, Tingzhou Rd., Taipei, Taiwan

Table S2. A pre-test of light reduction and microenvironment changes from three different netting types

In order to minimize the effects of the nettings on the willows’ microenvironments, we performed a pre-test on three different netting types (B: mesh size 27 mm, string thickness 0.12 mm, black; S: mesh size 18 mm, string thickness 0.12 mm, black; G: mesh size 18 mm, string thickness 1 mm, green) to determine which has the smallest effects in light reduction, ambient temperature and relative humidity. We purchased 7 potted willow saplings (c. 6 months old) from a flower market in Taipei on June 1st, 2010, and placed them in the campus garden at National Taiwan Normal University. We randomly assigned two saplings to a netting type, leaving one for control (un-netted). We used a wire frame to support the netting around the plant without any of the wire or netting touching the leaves. On July 12th, 2010 (a sunny day), we took three light luminance readings (TES-1335 Digital Light Meter, TES Electrical Electronic Corp., Shanghai, China) both inside and outside the nettings. We did the same set of measurement at 8 am and again at 2 pm on the day (N = 12 for each netting type). From July 12th to 14th of 2010 for a consecutive 48-hr period, we recorded ambient temperature (°C) and relative humidity (%) (H08-032-08 HOBO® Temp/RH Data Logger) inside the nettings (c. 20 cm from the plant). The temperature and humidity were recorded every 30 mins, which were averaged to obtain hourly readings. We tested the effects of netting type on temperature and humidity using generalized linear models with Poisson distribution, the hour was treated as a fixed effect (24-hour time block) and the day as repeated measures (on the same individual sapling). There was no overall difference in temperature between different netting types and control (netting: F3,292 = 0.09, P = 0.97; hour: F23,292 = 4.64, P < 0.0001). However, there was a marginal overall difference in humidity between different netting types and control (netting: F3,292 = 2.51, P = 0.06; hour: F23,292 = 27.69, P < 0.0001). Post-hoc comparisons between the control and each of the three netting types indicate no significant differences in either temperature or humidity (t values for the post-hoc comparisons are provided in the Table). Based on these results, we selected the netting type B for our experiment.

Netting type / Light / Microenvironment
N / Inside (lux) / Outside (lux) / % Reduction / DF / Temperature (°C) / Relative humidity (%)
Mean / SE / Mean / SE / Mean / SE / LS-mean / LS-SE / t / LS-mean / LS-SE / t
B / 12 / 19904 / 4816 / 23708 / 6963 / 6 / 7 / 292 / 28.6 / 0.5 / 0.45N.S. / 88.3 / 2.4 / 0.30 N.S.
S / 12 / 11867 / 3202 / 12782 / 3331 / 7 / 5 / 292 / 28.4 / 0.5 / -0.16 N.S. / 93.2 / 2.5 / -1.46 N.S.
G / 12 / 9409 / 2083 / 11051 / 1905 / 18 / 7 / 292 / 28.4 / 0.5 / -0.14 N.S. / 83.9 / 2.3 / 0.76 N.S.
Control / -- / -- / -- / -- / -- / -- / -- / 292 / 28.2 / 0.8 / -- / 87.0 / 3.4 / --