The yield of animal-pollinated crops is threatened by bee declines, but its precise sensitivity is poorly known. We therefore determined the yield dependence of Hokkaido pumpkin in Germany on insect pollination by quantifying: (i) the relationship between pollen receipt and fruit set and (ii) the cumulative pollen deposition of each pollinator group. We found that approximately 2500 pollen grains per flower were needed to maximize fruit set. At the measured rates of flower visitation, we estimated that bumblebees (21 visits/flower lifetime, 864 grains/visit) or honeybees (123 visits, 260 grains) could individually achieve maximum crop yield, whereas halictid bees are ineffective (11 visits, 16 grains). The pollinator fauna was capable of delivering 20 times the necessary amount of pollen. We therefore estimate that pumpkin yield was not pollination-limited in our study region and that it is currently fairly resilient to single declines of honeybees or wild bumblebees.
Single visit deposition of pumpkin pollen of three bee species groups in 2015
Original source: single visit deposition (SVD) experiments in the field, pollen extracted by acetolysis; Open Office org Calc was used to create the file; abbrevations: "species" = bee species group ("bumble" = Bombus terrestris, B. lucorum; "halictid" = several Halictidae, mainly Lasioglossum malachurum; "honey" = Apis mellifera), "IT.span" = intertegular span.
SVD.bee-species_pumpkin_2015.csv
R script for the analysis of the single visit deposition data
Data analysed "SVD.bee-species_pumpkin_2015.csv"; software R 3.2.2 (2015) used
R_script_SVD.R
Pollen grains at bagged and open anthers in 2012 and 2015
Data collected in the field; Open Office org Calc used to create the data file.
pollen.anther.csv
R script analysing pollen at the anther data
Data file used for the analysis "pollen.anther.csv", software R 3.2.2 (2015) used to create the file.
R_script_pollen.anther.R
Visitation rates of bee groups in videos in 2014
Visitation rates collected by in total 54 hours of video recording in 18 fields in 2014. Open Office Org Calc was used to create this data file. "no.visits" = number of visits by the corresponding species groups, "species" = species group {"bumble" = Bombus terrestris, B. lucorum, B. lapidarium; "halictid" = several Halictidae, mainly Lasioglossum species; "honey" = Apis mellifera}, "start.time" = starting time of the video at three different time periods (7:00 am, 8:30 am, 10:00 am).
vis.rate_video2014.csv
Handling time of bee individuals (video data) in 2014
Handling time of the 2100 bee individuals are derived from the videos recorded in 18 fields in 2014. Open Office org Calc was used to create the data file. Abbreviations: "species" = three different bee species groups ("bumble" = Bombus terrestris, B. lucorum, B. lapidarius; "halictid" = several Halictidae species, mainly Lasioglossum species; "honey" = Apis mellifera), "handling.time.s" = total time bees spent handling the flower in seconds, "nectar.time.s" = total time bees spent on/at the stigma and feeding nectar, "group.halictid" = halictid species were divided into two size classes (length ~ 6 mm or ~ 8 mm), "successful.visit" = visit, where stigma was touched = nectar.time.s > 0; "start.time" = starting time of the video divided into three time periods (7:00 am, 8:30 am, 10:00 am).
handling.time_video2014.csv
R script analysing video data
Data files analysed "vis.rate_video2014.csv" and "handling.time_video2014". Software R 3.2.2 (2015) was used.
R_script_video.data_lmer.R
Pollen-yield experiment data from 2014 and 2015
Data from hand-pollination experiments in fields with different levels of pollen deposition in 2014 (5 levels) and in 2015 (7 levels). Details see manuscript and Table S1 in the supplementary material. Open Office Calc used to create this file. Abbreviations: "harvestable" = 1, if pumpkin fruits could be harvested, "marketable" = 1, if pumpkin fruits weigh more than 800 g.
pollen.yield.2014_2015.red.csv
R script analysing the hand-pollination data
Data files used "mean_hpa.csv" and "pollen.yield.2014_2015.red". Software R 3.2.2 (2015) used for analysis.
R_script_yield.R
Calculated pollen deposition per bee species group
Formulas used for the calculation from "R_script_SVD". Data used in the formulas from field data "handling.time_video2014.csv", "vis.rate_video2014.csv", "SVD.bee-species_pumpkin_2015.csv", one sheet per bee species group (d.bumble, d.honey, d.halictid). Microsoft Excel used to create the file.
calculated deposition.model.xls
R script modelling the contribution of bee groups to pumpkin yield
Single visit pollen deposition data is the calculated data from the file "calculated deposition.model.xls". Data file used "mean_hpa.csv". Software R 3.2.2 used.
R_script_model.R
Mean values of fruit set per pollen deposition level
Mean values of set of harvestable pumpkins per pollen deposition level derived from data file "pollen.yield.2014_2015.red.csv". Open Office Calc used to create the file. Abbrevations: "pollen.est" = estimated level of pollen deposition, "mean" = mean value of set of harvestable pumpkins, "mp2" = mean value + E-13 in percent.
mean_hpa.csv