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 a 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 southwest of Buenos Aires province, Argentina. We dissected the quantity components of the pollinator effectiveness landscape by estimating two quantitative subcomponents: visitation rate and flower tripping rate. Also, we estimate pod set as a qualitative component without dissecting it in subcomponents. 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 bee flower tripping rate and pod set were as high as managed ones. In fact, wild bees were more effective in promoting flower tripping than one of the managed bees (A. mellifera). This approach allowed us to assess which effectiveness components and 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.