DOI: 10.5061/dryad.brv15dvjt
title: Wildflower plantings and honeybee competition impact nutritional quality of wild bee diets

description: Wildflower habitats planted along field borders are a widely promoted
 strategy for supporting bees in agricultural landscapes. However,
 honeybees (Apis mellifera), which are often stocked at high densities in
 crop lands, can compete with wild bees for pollen and nectar, potentially
 limiting the successfulness of wildflower plantings in supporting diverse
 bee communities. Using weekly samples of five study sites in Northern
 California we assessed how plants in pollinator-friendly seed mixes varied
 in their ability to provide bees with abundant and nutritious pollen under
 intense honeybee competition. We quantified pollen production, protein and
 lipid content, and end-of-day pollen availability for different plant
 species. We also sampled bee visits to flowers and assessed the
 composition of pollen on bee bodies. Using these data, we investigate how
 the nutritional quality of pollen in wildflower plantings and honeybee
 abundance impacted native bee pollen nutrition. Bees collected more
 nutritious pollen (i.e., pollen with more protein) from plantings with
 more nutritious plant species (i.e., sites with more high-protein plants).
 However, as honeybee abundance increased, the nutritional quality of
 native bee diets declined. We also detected important interactions between
 honeybee abundance and the nutritional quality of flowers in plantings,
 such that, for some bee taxa, there was no impact of competition on pollen
 diet quality in high-nutrition plantings.
description: <strong>Please see the meta data file (README.md) for more
 detailed information about variable names and their
 interpretation. </strong>
 <strong><em>Study sites</em> <em>and
 pollinator surveys</em> - </strong>We conducted this work in
 the California Central Valley at five replicated wildflower plantings
 neighboring conventionally managed Almond orchards. Sites varied in
 honeybee abundance due to spatial variation in the placement of commercial
 apiaries. In 2017 and 2018, we surveyed bees and their visits to flowering
 plants over four sample rounds from April – May. We netted insects
 actively visiting flowers during 10-minute walks of two 100
 m<sup>2</sup> transects sampled once in the morning and once
 in the afternoon (40 minutes total). Netted pollinators were collected
 individually in separate vials to minimize pollen contamination and
 euthanized using dry ice, except for bumblebee queens, which we
 identified, swabbed for pollen, and released. We collected up to twenty
 honeybees during netting transects and counted any additional honeybees.
 Bees were identified to species or morphospecies by expert taxonomists
 (Skyler Burrows, USDA Bee Lab, Logan, Utah, and Joel Gardner, University
 of Manitoba, Canada). In statistical analyses (and in data provided here),
 we grouped bees into five categories: <em>Apis mellifera</em>,
 <em>Bombus</em> spp., Megachilidae, Halictidae, and “Other
 bees” (comprising Andrenidae, Colletidae, and non-corbiculate Apidae). The
 datafile "beeflow_df.csv" contains information on pollinator
 species identifications, associated taxonomic groupings used in
 statistical analyses, the identity of the flowering plant species a given
 pollinator was visiting when collected, and site-level information on
 honey bee abundance. <strong><em>Pollen
 availability in flowers -</em></strong> At the end of each
 sampling day, we assessed pollen availability for the most abundant and
 well-represented plant species: <em>Clarkia unguiculata, Clarkia
 williamsonii, Collinsia heterophylla</em>,<em> Eschscholzia
 californica, Lupinus densiflorus</em>, and<em> Phacelia
 californica</em>. We measured pollen availability as the proportion
 of dehisced anthers with pollen visible to the naked eye, using one to
 three flowers on 10-20 “open-pollinated” (i.e., unmanipulated) plants. The
 datafile "pollen_avail_df.csv" contains information on the
 number of dehisced anthers with and without pollen for flowers of
 different plant species sampled at different sites. 
 <strong><em>Nutritional quality of pollen from
 different plant species</em></strong> -  We grew monospecific
 flower plantings for each of the ten most-visited plant species
 (representing 96% of floral visits and 92% of bee-collected pollen). We
 covered each planting with organza fabric prior to anthesis to prevent
 insect visitation, collected fresh pollen from flowers, and assessed
 pollen protein and lipid content. As we harvested pollen for macronutrient
 analyses, we also collected data on the number of florets sampled and the
 mg of pollen extracted from those florets, giving us an estimate of pollen
 production per floret.
 <strong><em>Assessing pollen diet composition 
 </em></strong>– In the lab, we used fuchsin-tinted jelly cubes
 to remove and stain pollen from bee bodies, which we then melted onto
 microscope slides. When swabbing bees, we focused our effort on scopae
 (i.e., pollen from specialized pollen-collection hairs), but also lightly
 brushed the head and thorax. For <em>Apis</em> and
 <em>Bombus</em>, we used tweezers to dislodge small clumps of
 pollen from multiple areas of corbiculae (i.e., pollen baskets). We
 identified pollen to species using light microscopy and a pollen reference
 collection. In 2018, we assessed pollen from corbiculae and scopae
 separately from pollen removed from other body parts, but ultimately
 pooled pollen from both sources for each specimen in our analyses. Using
 data on the composition of pollen on bee bodies and information on the
 protein and lipid content of pollen from different plant species, we
 calculated the mean protein content and protein-to-lipid (P:L) ratios of
 pollen collected by each bee specimen sampled. In the datafile
 "beeflow_df.csv", these variables are named
 'bee.protein.prop' (estimated protein content of pollen on bee
 bodies) and 'PL.ratio' (estimated P:L ratio of pollen on bee
 bodies). When possible, we separately estimated the protein content and
 P:L ratios for bee scopal/corbicular loads (variable names:
 "load.protein.prop" and "load.PL.ratio"). 
 <strong><em>Estimating nutritional quality of
 wildflower plantings at time of sampling</em></strong> - We
 estimated nutrient availability in wildflower plantings for each site
 sample by calculating the mean protein-to-lipid (P:L) ratio and protein
 content of available pollen. In the datafile "beeflow_df.csv",
 these variables are named 'protein.prop.by.mg' (estimated
 protein content of pollen available in plantings at time of sampling) and
 'PL.ratio.by.mg' (estimated P:L ratio of pollen available in
 plantings at time of sampling). To generate these estimates, we used data
 on the composition of floral resources available in netting transects and
 data on the protein and lipid content of pollen from these plant species.
 On the same day and in the same transects where bees were collected, we
 assessed flowering species composition by counting and identifying all
 flowers in 10 evenly spaced 1m<sup>2</sup> quadrats. To
 account for the fact that not all plants produce the same amount of
 pollen, we weighted the contribution of different plant species by their
 pollen abundance, where pollen abundance was calculated as the number of
 florets of a given species counted during a site sample multiplied by the
 pollen production per floret of that same species.  
description: # Wildflower plantings and honeybee competition impact nutritional quality
 of wild bee diets. Journal of Applied Ecology. ## Description of the data
 and file structure Bee pollen nutrition and associated sampling data
 ("`beeflow_df.csv`"): This dataset provides information on each
 bee specimen collected, associated bee taxonomic data, the plant species
 the bee was visiting when collected, information on the estimated
 nutritional quality of pollen on bee bodies, as well as the estimated
 nutritional quality of pollen in wildflower plantings for the site and
 sample round in which the bee specimen was collected. Variable names are
 described below and more details about how we performed analyses can be
 found in the associated publication. * poll.species - pollinator species
 identity of sampled bee * poll.genus - genus of sampled bee * poll.family
 - family of sampled bee * bee.taxon - broader taxonomic grouping of bee
 species for analyses * plant.species - plant species the bee was visiting
 when collected * PL.ratio - estimated Protein to Lipid (P:L) ratio of
 pollen on sampled bee * bee.protein.prop - estimated protein content of
 pollen on sampled bee, measured as a proportion * bee.lipid.prop -
 estimated lipid content of pollen on sampled bee, measured as a proportion
 * load.PL.ratio - estimated Protein to Lipid (P:L) ratio of bee
 scopal/corbicular loads, NA stands for "not available" *
 load.protein.prop - estimated protein content of bee scopal/corbicular
 loads, measured as a proportion, NA stands for "not available" *
 total.honey – honey bee abundance, measured as the total number of honey
 bees visiting flowering plants during morning and afternoon netting
 transects * honey.scale – honey bee abundance, scaled from 0 – 1 (with 1
 being the max. honey bee abundance observed across all samples) * site –
 site name * sr – sample round * year – year in which data were collected *
 protein.prop.by.mg - estimated protein content of pollen available in
 plantings at time of sampling, measured as a proportion * PL.ratio.by.mg -
 estimated Protein to Lipid (P:L) ratio of pollen available in plantings at
 time of sampling Pollen availability data
 ("`pollen_avail_df.csv`"): This dataset provides information
 about pollen in flowers measured at the end of the day across different
 sites. Variable names are described below and more details about how we
 collected data and performed analyses can be found in the associated
 publication. * site – site name * sr – sample round * plant.code - field
 code used for plant species sampled (Clarkia unguiculata = CLAUNG, Clarkia
 williamsonii = CLAWIL, Collinsia heterophylla = COLHET, Eschscholzia
 californica = ESCCAL, Lupinus microcarpus var. densiflorus = LUPDEN,
 Phacelia californica = PHACAL) * unique.plant.id – unique id for the
 individual plant sampled during a given site / sample round *
 anthers.with.pollen – number of dehisced anthers with pollen visible to
 the naked eye * dehisced.anthers – number of dehisced anthers