Plant-flower visitor interactions in dry cryophilic grasslands of Sierra de Guadarrama

We collected data throughout the flowering period (13 June to 28 July 2011) for a total of 10 census days for each sampling site at Nevero and 11 census days for each sampling site at Peñalara. There was one additional census day at Peñalara in order to balance the number of hours surveyed at the two localities (approximately 160 hours per site). Weather conditions determined the number of census days, as warm, dry and light wind conditions are unusual in high-mountain environments. Observations were made on sunny days without wind from 10:00 to 18:00 h when the environmental conditions at these altitudes allow visitor activity. To collect visitation data, we established two 60 x 100m sampling plots at each locality (Pastures and Encroached Pastures) where we established 10 linear transects across the width of the plots (60m long and 5m wide).
We made successive walks through the line transects, noting the identity and number of contacts between plant and insect species. This methodology was used to observe the complete area of each sampling plot. We recorded a plant-flower visitor interaction when an insect maintained contact with the reproductive organs of a flower for more than 1 second. Thus, all flowering visiting insects that feed on flowers were recorded, regardless of the efficacy of their visit. The two sampling sites at each locality were simultaneously surveyed by two work teams. Insects were captured and determined to the lowest taxonomic category possible with the help of experts. Table S1 contains acronyms used for plant and visitors.