Effectiveness Landscape of Crop Pollinator Assemblages: Implications to Pollination Service Management

Abstract

There is a growing consensus that the world is facing a pollination crisis. To mitigate crop pollination deficits, some management strategies include the massive introduction of managed bee species, yet quite often they are applied blindly, as information on crop pollination effectiveness for each single pollinator species of assemblages is usually not available. Therefore, the introduction on managed species is not always the best option to improve crop yields. Here, by using the highly pollinator-dependent alfalfa crop (Medicago sativa L.) as case study, we propose the use of the effectiveness landscape framework to identify key crop pollinator species. According to this framework, in a mutualistic interaction, each species effectiveness is represented by the product of a quantitative component and a qualitative one, these being measures of the outcomes of this interaction. We applied this framework for two managed and four wild bee species that visit alfalfa in fields in southwest of Buenos Aires province, Argentina. We dissected the quantity and quality components of pollinator effectiveness landscape by estimating three subcomponents: visitation rate, flower tripping rate as quantitative subcomponents and pod set as a qualitative subcomponent. Our results showed that the contribution of both components and the resulting pollinator effectiveness varied among pollinator species, indicating a contrasting effectiveness of different bee species on alfalfa pollination. For example, pollinator effectiveness was higher for managed than for wild bees, as consequence of their very high visitation rate, however, wild bees flower tripping rate and pod set were as high as managed ones. In fact, wild bees were more efficient in promoting flower tripping than one of the managed bees (A. mellifera).  This approach allowed us to assess which effectiveness subcomponents make pollinator species more or less effective, thus providing valuable information to identify key species to be enhanced to help in closing yield gaps. We suggest that the application of the effectiveness landscape framework would be useful to develop strategies to improve crop pollination service in pollinator-dependent crop systems.

Keywords: alfalfa, Apis mellifera, crop pollination, flower tripping, effectiveness landscape, Megachile rotundata, pollination effectiveness, wild bees