DOI: 10.5061/dryad.p869n
title: Data from: Direct and indirect effects of shrub encroachment on alpine grasslands mediated by plant-flower visitor interactions

description: Mutualistic interactions structure ecological communities and they are
 strongly influenced by the combined effect of different drivers of global
 change. Land-use changes and global warming have elicited rapid shrub
 encroachment in alpine grasslands in recent decades, which may have
 detrimental outcomes for native alpine forbs. In spite of the importance
 of this process, we lack knowledge about how shrub encroachment modifies
 community-wide patterns of plant–pollinator mutualistic interactions.
 Based on the functional biodiversity hypothesis (FBH), which predicts
 higher pollinator biodiversity in species-rich plant communities, we asked
 whether the increase in nutritional resources available for pollinators
 due to shrub expansion modifies pollinator niche breadth and species
 richness, and whether these changes affect plant–plant interactions. For
 this purpose, we compared quantitative plant–flower visitor interaction
 network assemblages at replicated plots in two habitat types in dry
 cryophilic grasslands of Sierra de Guadarrama (Spain): (i) encroached
 pastures (EP) and (ii) pastures dominated by forb species where shrub
 species are absent (PA). As predicted by FBH, flower visitor richness
 increased in EP, but their niche breadth did not vary. Furthermore, shrubs
 had more interactions with flower visitors and received more visits per
 plant than forbs in EP in agreement with their significantly higher
 linkage and strength. Overall, results revealed that moderate levels of
 shrub encroachment affected the flower visitation patterns of forb species
 in alpine grasslands as flower visitor diversity increased and plant–plant
 competition for shared flower visitors became greater. These findings
 highlight the need to use an integrative approach to study the cascading
 effects of global change drivers on species interactions and their impact
 on the structure and functioning of threatened ecological communities.
description: Plant-flower visitor
 interactions in dry cryophilic grasslands of Sierra de
 GuadarramaWe 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.LaraRomero_etal_2016_FunctionalEcology.xlsxTable S1. Acronyms used for plant and visitorsTable S1 contains acronyms used for plant and visitors.TableS1_Lararomero_etal_2016_FunctionalEcology.xlsx