How the Functional Constitution of Plant Communities in Field Margins Affects Wild Bee Community Composition and Functional Structure

Abstract

Concerns about a global decline in pollinators have called for more knowledge about the drivers of wild pollinator abundance and diversity in agroecosystems. Maintaining flowering plants in agricultural field margins is often recommended as a cost-effective and efficient method of offering habitat for wild pollinator conservation. This research involved a three-year, multi-farm study, examining Mediterranean cereal field margins in order to investigate which general and functional characteristics of margin plant communities were important for sustaining wild bee abundance, diversity, community evenness and functional diversity. Wild bees were collected and identified to genus, and a database was compiled listing the morpho-physiological features and behaviours of the observed genera. A database was also compiled of the flowering plant species observed and relevant trait values. General and generalized linear models indicated that margins with a higher percentage of trees and shrubs and higher floral richness displayed positive effects on wild bee diversity and visits to flowers in Mediterranean cereal agroecosystems. They also indicated that high plant functional diversity, in terms of flower colour and morphology, as well as high nectar accessibility, were important to encourage bee visits and community evenness within wild bee assemblages in these field margins. This study stresses the importance of maintaining protected field margins and, when necessary to restore their functionality, sowing floral mixtures with diverse native species, including trees and shrubs, and providing plenty of accessible nectar and a diverse assortment of colours and shapes.