Pollinator and crop production data
A total of 133 unique data points with information on pollinator
visitation rate and pollinator contribution to crop production were
obtained from databases of previous studies, sampled in various crops in
the UK (Garratt et al. 2014b, a, c, 2016) and the Netherlands (De
Groot et al. unpublished data ). A unique dataset is defined by
their sampling year, crop species and spatial location (see dataset
details in Table 1, Fig. 2). Pollinator data was collected using
transects surveys over a defined distance and time, recording visitors
to crop flowers as Apis or non-Apis species (including
bees and hoverflies). At each site, pollinator contributions to crop
production were measured using pollinator exclusion treatments and
compared with open controls to establish a proportional contribution of
insect pollinators to production (for further methodological details see
Garratt et al., 2014a, 2014b, 2016, and De Groot unpublished data in
supplementary material).
Whenever studies provided more than one crop production metric, we
selected the most pertinent variable to define crop production: seed set
for oilseed rape, pod set for fava bean (Garratt et al. 2014b)
and fruit set for blueberry. For apple, studies conducted in the
Netherlands gave information on fruit quality, i.e., fruit weight. For
studies in apple orchards in the UK, data available concerned final
fruit set at harvest. For each experimental branch, the number of apples
which had developed on experimental inflorescences was recorded (see
Garratt et al., 2014a, 2014b, 2016).
As data from different studies applied different methodologies to
extract information on pollinators and pollination, we calculated
z-scores within each study for crop pollination (i.e., contribution of
pollinators to crop production) and pollinator abundances (Apisand non-Apis pollinators separately). This measure allows for the
standardisation of scores with respect to the other scores into the same
group (site/crop/year) (Garibaldi et al. 2011, 2015).