DOI: 10.5061/dryad.q2bvq83h7
title: Data from: Crop pollination services: complementary resource use by social vs solitary bees facing crops with contrasting flower supply

description: 1. Many farmers are facing high economic risks if pollinator declines
 continue or temporal and spatial variation in wild bee communities cause
 reduced pollination services. Co-flowering crops might compete for
 pollinators, while they also might facilitate the delivery of pollination
 services. This rarely studied topic is of particular interest with respect
 to the foraging decisions of bees from different functional groups and
 when more sparsely and mass-flowering crops are in bloom at the same time.
 2. The abundance of honey bees, bumble bees and solitary bees in
 strawberry fields was quantified with transect walks along a gradient of
 oilseed rape (OSR) availability (product of OSR land cover and temporally
 changing OSR flower cover). We established a pollination experiment with
 pollination treatments (open-, wind- and self-pollination) to study the
 effects of insect pollination on strawberry fruit weight and quality. 3.
 Changes in OSR availability exhibited contrasting effects on social versus
 solitary bees in strawberry fields. Bumble bees and honey bees were less
 abundant in strawberry fields when OSR availability was high, whereas
 solitary bees were facilitated. With more strawberry flowers we found more
 bees in general. 4. When flowers were open-pollinated they resulted in
 heavier fruits with better commercial grades compared to wind-and
 self-pollinated flowers. A higher bee abundance enhanced the strawberry
 fruit weight and quality but depended on flower order and variety. 5.
 Synthesis and applications. Sparsely flowering crops may compete with
 mass-flowering crops for social bee pollinators while solitary pollinators
 in the field might be even facilitated. To ensure best fruit weight and
 quality it can be beneficial to support bee abundance in the field. While
 some social and solitary bee species can be managed for pollination
 services, wild bees, in particular solitary species, should be conserved
 and promoted for stable crop pollination services in dynamic agricultural
 landscapes.
description: POLLINATOR ABUNDANCE We used standardised
 transect walks to sample flower-visiting bees in our study fields
 (strawberry fields in 8 landscapes). We had four observation periods
 during the strawberry flowering period in May and June. 2015 Flowering of
 both crops started around the end of April and co-flowering continued for
 four to five weeks depending on the location and weather conditions. Two
 transects (each 50 m x 4 strawberry rows) were established within the
 strawberry fields: one at the edge and one inside the field (15 m from
 edge) to account for edge effects. Each transect lasted 15 min and was
 conducted between 9 am and 6 pm while we visited each field in morning and
 afternoon hours. Hence, eight transects have been conducted in each
 strawberry field during the study period. For the observations we chose
 good weather conditions, i.e. days with a minimum temperature of 12°C, no
 rain, low wind speed and low cloud cover. Flower-visiting bees within the
 transect area were counted and identified to species level in the field or
 caught with an insect net for later identification in the laboratory.
 Solitary bees were identified by SB and Frank Creutzburg. Bee individuals
 that escaped from the insect net were not identified to species level, but
 their abundance was counted if they could be assigned to one functional
 group. Bee abundance is quantified as number of individuals per
 transect. We assigned the bees to functional groups
 according to their sociality and level of domestication (i.e. honey bees,
 bumble bees and solitary bees). However, we found one individual of
 <i>Halictus tumulorum</i> which is thought to be primitively
 eusocial. Due to its morphological similarity with other solitary bees, we
 included it in the group of solitary bees for our analyses.
 We quantified strawberry flower cover by counting the number of
 open flowers along two meters of a strawberry row within each transect
 area (edge and inside of the field separately).
 POLLINATION EXPERIMENT Fruit weight and
 commercial grades To investigate the importance of
 insect pollination for strawberry fruit quantity and quality, we
 established a pollination experiment with three treatments (open-, wind-
 and self-pollination). Open-pollinated flowers were left open to allow
 access for all flower-visitors as well as for airborne pollen. To exclude
 only insects, but allow airborne pollen flow, we bagged individual flowers
 in bags with mesh sizes of 1 mm in the wind-pollination treatment. We used
 Osmolux bags (Pantek, France), which are permeable for water vapour
 (http://www.pantek-france.fr/agriculture.html), for the self-pollination
 treatment (exclude insects and airborne pollen). All bags were removed
 after blooming to standardise the fruit ripening. In
 total, we had 40 plants per field, 20 plants at the edge and 20 plants in
 the inside of the strawberry field according to transect location. Five
 plants per transect location were assigned to the self- and
 wind-pollinated treatment and ten plants to the open-pollination
 treatment. Strawberry flowers can be assigned to different orders
 according to their temporal occurrence and position on the stalk. One
 primary flower (first order) usually occur first on the main stalk,
 followed by two secondary flowers which branch off the main first stalk,
 and followed by up to four third order flowers which branch off the second
 stalks. Generally, higher flower orders produce berries with a reduced
 size and weight. For this reason, we included only fruits from 1st to 2nd
 flower orders. Every strawberry fruit was weighted directly after harvest
 and categorized into commercial grades with respect to size, shape and
 colour according to the European Commission. Commercial grades were
 categorized as G1/E, where we pooled Grade Extra and one, G2 as Grade two
 and NM for non-marketable fruits. We used a subset of
 three observation periods since the combined data of bee abundance and
 subsequent fruit yield and quality is only available for three points in
 time.