Wild bee and floral diversity co‐vary in response to the direct and indirect impacts of land use

Alexandra D Papanikolaou,Stuart P M Roberts,Ingolf Kühn,Oliver Schweiger,Mark Frenzel,Michael Kuhlmann,Simon G Potts,Peter Poschlod

doi:10.1002/ecs2.2008

Abstract

AbstractLoss of habitat area and diversity poses a threat to communities of wild pollinators and flowering plants in agricultural landscapes. Pollinators, such as wild bees, and insect‐pollinated plants are two groups of organisms that closely interact. Nevertheless, it is still not clear how species richness and functional diversity, in terms of pollination‐relevant traits, of these two groups influence each other and how they respond to land use change. In the present study, we used data from 24 agricultural landscapes in seven European countries to investigate the effect of landscape composition and habitat richness on species richness and functional diversity of wild bees and insect‐pollinated plants. We characterized the relationships between the diversity of bees and flowering plants and identified indirect effects of landscape on bees and plants mediated by these relationships. We found that increasing cover of arable land negatively affected flowering plant species richness, while increasing habitat richness positively affected the species richness and functional diversity of bees. In contrast, the functional diversity of insect‐pollinated plants (when corrected for species richness) was unaffected by landscape composition, and habitat richness showed little relation to bee functional diversity. We additionally found that bee species richness positively affected plant species richness and that bee functional diversity was positively affected by both species richness and functional diversity of plants. The relationships between flowering plant and bee diversity were modulated by indirect effects of landscape characteristics on the biotic communities. In conclusion, our findings demonstrate that landscape properties affect plant and bee communities in both direct and indirect ways. The interconnection between the diversities of wild bees and insect‐pollinated plants increases the risk for parallel declines, extinctions, and functional depletion. Our study highlights the necessity of considering the interplay between interacting species groups when assessing the response of entire communities to land use changes.

Highlights

Land cover change is a major threat to biodiversity and ecosystems leading to changes in species richness, abundance, and composition (Sala et al 2000, Millennium Ecosystem Assessment 2005, Newbold et al 2015)
We found that increasing cover of arable land negatively affected flowering plant species richness, while increasing habitat richness positively affected the species richness and functional diversity of bees
We found that bee species richness positively affected plant species richness and that bee functional diversity was positively affected by both species richness and functional diversity of plants

Summary

INTRODUCTION

Land cover change is a major threat to biodiversity and ecosystems leading to changes in species richness, abundance, and composition (Sala et al 2000, Millennium Ecosystem Assessment 2005, Newbold et al 2015). Decreasing cover of semi-natural areas leads to declines in wild bee species richness and abundance (Steffan-Dewenter et al 2002, Le Feon et al 2010, Papanikolaou et al 2017) and to reduced wild bee visitation rates and fruit set of different crops (e.g., Holzschuh et al 2012, Klein et al 2012). Less is known regarding the effect of semi-natural areas on native plant diversity and pollination success, increased cover of semi-natural habitats has been shown to be associated with higher plant species richness (Billeter et al 2008) and increased visitation rates of native plants (Steffan-Dewenter et al 2001), while increasing proximity to semi-natural areas has been found to increase seed production of native plants (Schmucki and de Blois 2009, Jakobsson and Agren 2014) with potential positive effects on wild plant communities. We focus on the effect of landscape composition on species richness and functional diversity of insect-pollinated plants and wild bees. Taking into account the interdependence of flowering plants and their pollinators, we expect that landscape composition and habitat diversity have both direct and indirect effects on plant and bee diversity; that is, changes in plant diversity caused by altered landscape properties (direct effect) may subsequently cause changes in bee diversity (indirect effect) or the other way around

MATERIALS AND METHODS

RESULTS

DISCUSSION