DOI: 10.5061/dryad.vdncjsxwf
title: Adjacent crop type impacts potential pollinator communities and their pollination services in remnants of natural vegetation.

description: Aim: Pollination plays a crucial role in the conservation of many
 plant species persisting in fragmented, human-dominated landscapes.
 Pollinators are known to be instrumental in maintaining genetic diversity
 and metapopulation dynamics for many plant species and are important for
 providing ecological services that are essential in agricultural
 landscapes where populations of native plants are highly isolated.
 Numerous studies have explored the value of remnant native vegetation for
 supporting pollination services to crop species; yet the effect of
 mass-flowering crops on the pollinator communities and the pollination
 services they provide to native plant communities persisting in fragmented
 landscapes are less well-understood. Here, we assess the
 influence of the presence and phenology of a mass-flowering crop to
 pollinator community structure, abundance and pollen load composition in
 remnant vegetation in complex agricultural landscapes. 
 Location: South-west Western Australia, Australia.
 Methods: We recorded the composition and abundance of insect
 flower visitors and their pollen loads in isolated remnants of York
 gum-Jam woodlands adjacent to canola (insect-attracting) or wheat
 (non-insect-attracting) fields over two years. 
 Results: All bees were much more sensitive to adjacent crop type
 (neighbouring canola or wheat) than non-bee pollinators. Honeybees were
 the most abundant pollinators in canola fields during peak flowering.
 Honeybee abundance increased in canola-adjacent reserves post-canola
 bloom, potentially indicating a movement into reserves as crop flowering
 waned. Native bees were the most diverse in remnant
 vegetation.  Pollen loads of native bees were more mixed
 (increased pollen richness and evenness) when sampled next to canola
 fields compared to wheat fields.  Main conclusion: The
 availability of potential insect pollinators to remnant wildflower
 communities in agricultural landscapes is context dependent. Whether
 sampled communities were adjacent to wheat or canola in a landscape
 significantly impacted the abundance of potential pollinators in certain
 landscape elements, but not others, and the composition of pollen loads
 carried by these insects. Results offer novel insights about the influence
 of landscape context on pollinator communities and the potential
 pollination services available for the conservation of native plant
 species in highly fragmented agricultural landscapes.
description: <em><strong>Study
 System</strong></em> This study was conducted across 235 km of the
 central wheatbelt of SW Western Australia (distance from north-most to
 southeast-most remnant) in July-September of 2015 and 2016 (Supplementary
 Figure 1). The Eucalypt woodlands of the Western Australian Wheatbelt
 account for a substantial proportion of the native vegetation in the
 region (about 44.6 percent) though are made up of fragmented patches
 dispersed within an agricultural matrix of wheat, canola, barley, oats,
 and lupins (DAWE, 2015). A major sub-group of this woodland type in this
 region is the York gum-Jam woodlands (YGJW), currently listed as a
 Priority III Critically Endangered Ecological Community under the EPBC Act
 (DAWE, 2015). This woodland supports an overstorey dominated by two main
 tree taxa, <em>Eucalyptus
 loxophleba</em> subsp. <em>loxophleba</em>(York gum)
 and <em>Acacia acuminata</em> (Jam). The understorey in these
 woodlands is a mosaic of largely native shrubs, perennial grasses, and
 annual forbs (Dwyer, et al., 2015). Annual forbs in this system are
 dominated by representatives of the Asteraceae, Goodeniaceae, and
 Araliaceae families with some common species known to require insects for
 pollination (Lai et al., 2015; Staples et al., 2016). The canopy trees in
 this system do not flower at the same time as canola and wheat, but the
 wildflower understorey does, with flowering starting at approximately the
 same time as canola (in July), extending up to two months after canola and
 wheat flowering stops in late August. In this study region, we selected 24
 YGJW remnants (12 each year: six canola (<em>Brassica
 napus</em>), six wheat (<em>Triticum </em>sp.)), each
 greater than 0.1km2 and in intact condition (DAWE, 2015), supporting
 diverse annual wildflower communities. Some remnants were included in both
 study years, but with swapped categories between years due to crop
 rotations, while others were only studied for one year (see Supplementary
 Table 1). Across the two years, we established 324 sampling plots; with
 252 sampling plots inside remnants, which were then divided into two
 groups: 108 core plots (&gt;200 m from the agricultural edge) and 144
 remnant edge plots. Remnant plots were divided among those adjacent to
 wheat and those adjacent to canola fields (&lt;50 m from agricultural
 edge; Supplementary Figure 1). The remaining 72 sampling plots were
 established in canola fields adjacent to each woodland remnant bordered by
 canola (Supplementary Figure 1; Supplementary Table 1). Initial surveys of
 wheat fields revealing no flower visiting insects, so these were not
 surveyed further.  <em>Plot-level
 variables</em> In the 24 remnants, vegetation surveys and
 woodland “remnant” characteristics were recorded in 15 x 15 m plots during
 the months of July-September in 2015 and 2016. Measurements included: %
 bare soil within plot, proportion woody debris (i.e., dead logs)
 within each plot (from 0
 to 1 – estimated as the amount of the plot containing woody debris that
 could be used as nesting substrate for solitary bees), % flower cover in
 the plot, and a categorization of the understorey community by dominant
 flowering plant life-history strategy (i.e. predominately native forbs,
 exotic forbs, shrubs or grasses). These measurements were repeated three
 times in each plot, one survey conducted during each flowering season. The
 same data were collected for remnants adjacent to canola, as well as an
 estimate of the canola flowering phenological stage in the relevant
 adjacent field, using three categories: ‘peak’, &gt;70% inflorescences
 flowering; ‘past-peak’, between 40-70%; and ‘late’, end of the flowering
 period with &lt;40% open flowers. Other variables included size of
 remnant (km<sup>2</sup>), size of the agricultural field
 adjacent to the study remnants (km<sup>2</sup>) and distance
 of each plot within the remnant to the nearest agricultural edge
 (m).  <em>Sampling of potential
 pollinators</em> Potential pollinators were collected three times
 from each plot across the canola flowering season (once during early
 canola bloom, peak canola bloom and late canola bloom). We sampled only on
 sunny or partially cloudy, still days in 20-minute time periods during
 peak insect activity times (10 am – 3 pm). The 20-minute timer was paused during insect
 capture and handling time. Preliminary surveys found minimal (often no)
 insect activity outside of this peak activity window possibly due to low
 temperatures (mean minimum temp of 6.1°C for July) early in the morning and late in
 these winter afternoons. Potential pollinators were collected only if they
 landed on a flower and were observed making contact with the anthers or
 stigmas of a flower. We were not able to directly assess whether each
 insect was actively pollinating during each visit, and thus note that
 collected insects in this study are potential pollinators only.  For
 conciseness, however, we refer to them as “pollinators”. Insects were
 captured using sterile plastic containers or bags to ensure all body
 pollen was accounted for and no cross contamination of pollen from
 different individuals occurred. All insects were identified by experts to
 the lowest taxonomic level possible, using collected specimens. Given the
 limited taxonomic work that has been done on Western Australian bees and
 flies, most species were only identifiable to the family or genus
 level.  For species whose taxonomy was unclear, we categorized into
 morphospecies. Due to low samples sizes (n = 36 individuals), wasps were
 excluded from the study. Sampling efforts in canola fields were limited to
 the edge of the crop fields due to access restrictions. All honeybees
 collected in this study were considered to be feral (unmanaged), as
 managed honeybee hives were not used by the canola growers in this region
 during the study years. This is a very sparsely populated region of
 Australia (Perenjori Shire has a population density of 0.07
 people/km2 (ABS, 2017)) and thus we are confident we were aware of all
 homesteads and know that no local farms or households were keeping
 honeybees during the study period. Though feral honeybees are known to
 reach very high colony densities in Australia (Cunningham, et al.,
 2022). <em>Pollen load
 collection </em> We recorded pollen load (the composition and
 number of pollen grains) found on 893 of the 923 individual pollinators
 collected in the 2015 season. The remaining 30 insects had no pollen on
 their bodies. Pollen loads were assessed by swabbing each collection bag
 and insect body with Fuchsin jelly, which was then melted on a glass slide
 and prepared as per Kearns and Inouye (1993) (see Supplementary Material
 Methodology 1). We also created a pollen library to help with pollen
 compositional assessment, using the same Fuchsin jelly approach, where a
 voucher specimen of every flowering plant species in each remnant during
 each visit. Details regarding pollen identification and counting can be
 found in the Supplementary Material Methodology 2.