Impact of human disturbance on bee pollinator communities in savanna and agricultural sites in Burkina Faso, West Africa.

Dethardt Goetze,Kathrin Stenchly,Drissa Coulibaly,Souleymane Konaté,Kangbeni Dimobe,Stefan Porembski,K Eduard Linsenmair,Ingolf Steffan‐Dewenter,Alain Pauly,Katharina Stein

doi:10.1002/ece3.4197

Abstract

All over the world, pollinators are threatened by land‐use change involving degradation of seminatural habitats or conversion into agricultural land. Such disturbance often leads to lowered pollinator abundance and/or diversity, which might reduce crop yield in adjacent agricultural areas. For West Africa, changes in bee communities across disturbance gradients from savanna to agricultural land are mainly unknown. In this study, we monitored for the impact of human disturbance on bee communities in savanna and crop fields. We chose three savanna areas of varying disturbance intensity (low, medium, and high) in the South Sudanian zone of Burkina Faso, based on land‐use/land cover data via Landsat images, and selected nearby cotton and sesame fields. During 21 months covering two rainy and two dry seasons in 2014 and 2015, we captured bees using pan traps. Spatial and temporal patterns of bee species abundance, richness, evenness and community structure were assessed. In total, 35,469 bee specimens were caught on 12 savanna sites and 22 fields, comprising 97 species of 32 genera. Bee abundance was highest at intermediate disturbance in the rainy season. Species richness and evenness did not differ significantly. Bee communities at medium and highly disturbed savanna sites comprised only subsets of those at low disturbed sites. An across‐habitat spillover of bees (mostly abundant social bee species) from savanna into crop fields was observed during the rainy season when crops are mass‐flowering, whereas most savanna plants are not in bloom. Despite disturbance intensification, our findings suggest that wild bee communities can persist in anthropogenic landscapes and that some species even benefitted disproportionally. West African areas of crop production such as for cotton and sesame may serve as important food resources for bee species in times when resources in the savanna are scarce and receive at the same time considerable pollination service.

Highlights

During the last century, conversion of natural habitats and land-use intensification at habitat and landscape scale have been the major drivers of global environmental change in terrestrial ecosystems (Sala et al, 2000)
Our findings suggest that wild bee communities can persist in anthropogenic landscapes and that some species even benefitted disproportionally
West African areas of crop production such as for cotton and sesame may serve as important food resources for bee species in times when resources in the savanna are scarce and receive at the same time considerable pollination service

Summary

Introduction

Conversion of natural habitats and land-use intensification at habitat and landscape scale have been the major drivers of global environmental change in terrestrial ecosystems (Sala et al, 2000). Many pollinators visit crop habitats for foraging, but might need to return to natural habitats to complete their reproductive cycle because of the frequent disturbance regime in agricultural fields (Greenleaf, Williams, Winfree, & Kremen, 2007; Holzschuh, Steffan-Dewenter, Kleijn, & Tscharntke, 2007). This underlines the importance of natural and seminatural habitats which can provide spillover (i.e., movement of organisms and their function between natural habitats and agricultural sites) of pollinators and their pollination services to nearby cropland and vice versa (Blitzer et al, 2012)

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Discussion

Conclusion