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 unpublished data ).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pollinators to production (for further methodological details see Garratt et al., 2014a, 2014b, 2016, and De Groot unpublished data in supplementary material).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).