This post is written by Katie James, PhD Research Student, Natural Resources Institute, University of Greenwich, U.K.

The role of pollinator diversity in crop production

Pollinators play an integral role in crop production within agricultural landscapes due to the part they play in ensuring crop plant sexual reproduction by the transfer of pollen between crops. Studies have shown that greater diversity in pollinator networks results in crops that have higher yields, as well as fewer malformations (Blitzer et al., 2012) which can make the crop undesirable for commercial use due to a lower marketable quality. But the mechanisms within species diversity which facilitate greater yield and fewer malformations are not fully understood. The few studies that have explored the interrelationships between pollinator guilds on crop production and nutritional composition have shown that open-pollinated crops have a higher fat and vitamin E content (Brittain et al., 2014), and are of a better economic quality due to higher weight, fewer malformations and higher graded quality fruits compared to single species or hand-pollinated crops (Abrol et al., 2019). Additionally, it has been shown that wild bees provide not only an economic benefit from higher quality yields but also better shelf life and lower sugar-acid ratios, allowing for better storability of fruit crops (Klatt et al., 2014).

The role of complementarity between pollinators

Previous research has shown that plant visitation from multiple pollinator species produces fruits at a greater economic rate, with higher marketability (Albano et al., 2009). This is attributed mainly to the varying morphologies, behavioral traits and visitation rates of differing pollinator species. The overlap between these traits and behaviors (also known as niche complementarity) is thought to be why a greater diversity of pollinators provides a higher quality, yield and marketable quality. Niche complementarity between pollinator communities can be exhibited across multiple scales including spatial, temporal, seasonally and diurnally (Brittain et al., 2014; Garibaldi et al., 2016; Rader et al., 2013). The concept of niche complementarity, as well as promoting pollinator diversity, acts as a buffer to reduce the loss of pollination services due to species decline (Blüthgen et al., 2011; Inouye et al., 2015; Mallinger et al., 2014).

This overlap between species behavior and visitation is especially valuable in monoculture crops which produce flowers repeatedly over a season (such as strawberry). In high diversity pollinator communities, there will be more variation among pollinator species in their seasonality, thus ensuring more flowers are pollinated, which produces higher yields throughout the growing season whilst enhancing the mutualistic relationship between species, rather than competition for available resources (Grab et al., 2017). Additionally, the size of pollinators and how hairy they are also plays a key role in the effectiveness of a pollinator. Larger bee species, such as Xylocopa sp., which can collect large pollen loads and encounter a larger surface area of the flower, lead to a higher rate of pollination in single-flower visit (Mensah et al., 2011). Pollinators have been shown to visit different levels of floral canopy, possess different approaches to each flower and visit at varying times of the day. In apple orchards, bumblebees prefer the top canopy and tend to approach the flower from above, whereas hoverflies and wild bees prefer the lower canopy; thus, the combination of pollinator guilds provides a level of complementarity on smaller scales, as well as across a region. Species also vary in foraging behavior during the day, with foraging most frequent in the early morning and later afternoon in bees, and secondary pollinators in the morning and midday (Miñarro et al., 2018). Consequently, when considering the future of pollinator management, investigation is required to establish community-level management schemes to account for the role and importance of complementarity and how the interactions between species can be utilized to promote higher yields, quality, and if there is a direct relationship with micronutrient composition.

Future development and project aim

Most global crops that are rich in micronutrients are also pollinator dependent. Micronutrient deficiencies are expected to become more severe in the next 20-30 years due to several interrelated factors, including climate change and a growing human population that is expected to place increasing stress on food supply and production (Bongaarts, 2019). These pressures are likely to be most prominent in areas where micronutrient deficiency is already an issue and especially in developing countries (Eilers et al., 2011). Currently, micronutrient deficiencies are three times more probable in regions of high pollinator dependency for vitamin A and iron (Chaplin-Kramer et al., 2014). If pollinator populations and biodiversity continue to decline, this will induce negative impacts on nutrient availability, and ultimately human health. Therefore, there is a demand for research to find sustainable and non-intensive ways to promote micronutrient-rich food production by way of pollinator promotion, protection and integration within environmental management strategies. Over the next few years, this project aims to examine the relationships between different pollinators and establish the mechanisms which facilitate yield, quality, and micronutrient content of fruit and vegetable crops. It is hoped that this will inform the development and integration of sustainable agricultural management strategies and improve crop production in terms of micronutrient availability and economic enhancement.