DOI: 10.5061/dryad.2p2bh
title: Data from: How shrub encroachment under climate change could threaten pollination services for alpine wildflowers: a case study using the alpine skypilot, Polemonium viscosum

description: Under climate change, shrubs encroaching into high altitude plant
 communities disrupt ecosystem processes. Yet effects of encroachment on
 pollination mutualisms are poorly understood. Here, we probe potential
 fitness impacts of interference from encroaching Salix (willows) on
 pollination quality of the alpine skypilot, Polemonium viscosum. Overlap
 in flowering time of Salix and Polemonium is a precondition for
 interference and was surveyed in four extant and 25 historic contact
 zones. Pollinator sharing was ascertained from observations of willow
 pollen on bumble bees visiting Polemonium flowers and on Polemonium
 pistils. We probed fitness effects of pollinator sharing by measuring the
 correlation between Salix pollen contamination and seed set in naturally
 pollinated Polemonium. To ascertain whether Salix interference occurred
 during or after pollination, we compared seed set under natural
 pollination, conspecific pollen addition, and Salix pollen addition. In
 current and past contact zones Polemonium and Salix overlapped in
 flowering time. After accounting for variance in flowering date due to
 latitude, Salix and Polemonium showed similar advances in flowering under
 warmer summers. This trend supports the idea that sensitivity to
 temperature promotes reproductive synchrony in both species. Salix pollen
 is carried by bumble bees when visiting Polemonium flowers and accounts
 for up to 25% of the grains on Polemonium pistils. Salix contamination
 correlates with reduced seed set in nature and when applied
 experimentally. Postpollination processes likely mediate these deleterious
 effects as seed set in nature was not limited by pollen delivery.
 Synthesis: As willows move higher with climate change, we predict that
 they will drive postpollination interference, reducing the fitness
 benefits of pollinator visitation for Polemonium and selecting for traits
 that reduce pollinator sharing.
description: salix and pv phenology
 dataFlowering phenology data
 (Julian day) for Salix spp. and Polemonium viscosum specimens collected
 from 25 sites in the Colorado Rocky Mountains between 1907 and 2009. The
 location, altitude, mean minimum June temperatures, and the latitude and
 longitude estimated using Google Earth are provided for each
 specimen.2016 population
 surveyPollen counts on stigmas
 from naturally pollinated P. viscosum flowers. Pollen identified as Salix
 and P. viscosum (denoted by “pv” in the data file) were quantified using
 light microscopy. Salix pollen contamination was estimated as the
 frequency (proportion) of total pollen identified as Salix pollen. The
 site name, unique sample number (“sample ID), and the distance (m) from
 the focal plant to the nearest Salix spp. plant are
 included.pollen purity vs seed
 setAverage seed set per
 flower for naturally pollinated plants at Pennsylvania Mountain, Colorado.
 Pollination success (conspecific pollen deposition and germination rates)
 and contamination (proportion of pollen from Salix spp.) were quantified
 for one flower per inflorescence.pollination
 experimentData from the
 pollination contamination experiment. Individual plants found within
 groups of P. viscosum plants were randomly assigned to one of three
 pollination treatments: no pollen supplementation, conspecific (P.
 viscosum) pollen supplementation, and Salix spp. pollen supplementation.
 The plant number, group number, number of flowers pollinated, number of
 seeds produced, and average seeds per flower are
 provided.