Quantifying crop pollinator dependence and its heterogeneity using multi‐level meta‐analysis

Abstract

Biotic pollination can benefit crop production, but its effects are highly variable. To maximise benefits from this ecosystem service, we need a greater understanding of the factors that cause variation so that ecological intensification can be more effectively applied. We focus on understanding the benefits of pollination to faba bean Vicia faba. We use a literature review followed by multi‐level meta‐analysis to estimate overall benefits of pollination to faba bean yield and to quantify variation (heterogeneity) in these benefits associated with different contextual factors (e.g. plant genotype, growing environment). Our overall estimate of pollination benefit to faba bean yield, expressed as the percentage yield reduction without pollination, is 32.9% (confidence interval: 21%–43%). Based on the prediction intervals, which include the heterogeneity in pollination benefit, there is an 80% chance that pollination will increase yield of a faba bean crop. Half of all heterogeneity in pollination dependence was due to differences between plant genotypes. The number of beans per plant showed similar pollination dependence to yield mass per plant while pod number and number of beans per pod underestimated yield benefits. There was weak evidence to suggest pollination benefits vary between pollinator species, with honeybees showing a smaller yield increase. Differences in the experimental method used to assess pollination benefit did not significantly affect the estimate, including the growing environment, measurement scale, or whether the effects of experimental pollinator enclosures were controlled. This suggests that simplified experimental studies comparing yield of open‐pollinated and enclosed plants can provide reliable insights into pollination benefits across a large range of plant genotypes and landscapes. Synthesis and application. We found high variability in pollination benefits both between and within publications in our meta‐analysis. Plant genotype, how yield was measured, and pollinator species affected the level of pollination benefit. Despite variability in pollination benefits due to various contextual factors (both inside and outside of grower control), there is a high likelihood that biotic pollination will increase faba bean yield. Our findings support ecological intensification and specifically the management of pollinators to maximise pollination benefits to faba bean production.

High insect pest damage increases faba bean (Vicia faba) yield components but only in the absence of insect pollination

“…This is likely due to nectar deprivation at the start of the study, which meant that B. terrestris shifted from robbing nectar to legitimate visit later in the season when there were less flowers open. The low frequency of legitimate flower visits could, explain why the decrease in bean weight per plant due to lack of pollination (15%) was modest when compared to results from a recent meta-analysis of faba bean pollinator dependency (37% on average, Bishop & Nakagawa, 2021) or an experiment using the same cultivar (Tiffany) and bumblebee hives (61%, Raderschall et al, 2021). In addition, a recent field study using the cultivar Tiffany, found no dependence on insect pollination , indicating high variation in pollination benefit within this cultivar, likely mediated by environmental conditions.…”

“…Despite high variation between faba bean cultivars in their dependency on pollinators (Bishop et al, 2020;Bishop & Nakagawa, 2021), lack of insect pollination generally leads to lower yield in faba bean crops (Cunningham & Le Feuvre, 2013;Free & Williams, 1976;Raderschall et al, 2021;Riedel & Wort, 1960;Suso et al, 1996;Suso & del Río, 2015). This study confirms that lack of pollination decreases several faba bean yield components and is in line with a recent cage experiment using the same cultivar (Tiffany), where bean weight per plant and beans per pod but not individual bean weight benefitted from insect pollination (Raderschall et al, 2021).…”

“…Over the past 50 years, faba bean cropping area has been declining due to yield instabilities, associated to abiotic stress, pest and pathogen pressure (Karkanis et al, 2018), and possibly uneven insect pollination. Faba beans are partially dependent on insect pollinators (Bishop & Nakagawa, 2021). While insect pollination generally increases faba bean yield and yield stability (Suso & del Rio, 2015;Suso & Maalouf, 2010), pollination dependence within cultivars varies greatly, from -4 to 46% (loss in yield per plant without pollination) (Bishop et al, 2020).…”

Insect pest damage increases faba bean (Vicia faba) yield components but only in the absence of insect pollination

“…Over the past 50 years, faba bean cropping area has been declining due to yield instabilities, associated to abiotic stress, pest and pathogen pressure (Karkanis et al, 2018 ), and possibly uneven insect pollination. Faba beans are partially dependent on insect pollinators (Bishop & Nakagawa, 2021 ), with honeybees and bumblebees being the dominant pollinators in Northern Europe (Nayak et al, 2015 ; Raderschall et al, 2021 ). While insect pollination generally increases faba bean yield and yield stability (Suso & Maalouf, 2010 ; Suso & del Río, 2015 ), pollination dependence within cultivars varies greatly, from −4 to 46% (loss in yield per plant without pollination) (Bishop et al, 2020 ).…”

Paternal outcrossing success differs among faba bean genotypes and impacts breeding of synthetic cultivars

“…Faba bean is pollinated by wild and domestic bees. Without bee pollination, the yield is decreased by more than 30% (Bishop and Nakagawa 2021 ). Both self-pollen and cross-pollen are fertile and fully compatible (Link and Ghaouti 2012 ).…”