Abstract
The expansion of pollinator-dependent crops, especially in the developing world, together with reports of worldwide pollinator declines, raises concern of possible yield gaps. Farmers directly reliant on pollination services for food supply often live in regions where our knowledge of pollination services is poor. In a manipulative experiment replicated at 23 sites across an Ethiopian agricultural landscape, we found poor pollination services and severe pollen limitation in a common oil crop. With supplementary pollination, the yield increased on average by 91%. Despite the heterogeneous agricultural matrix, we found a low bee abundance, which may explain poor pollination services. The variation in pollen limitation was unrelated to surrounding forest cover, local bee richness and bee abundance. While practices that commonly increase pollinators (restricted pesticide use, flower strips) are an integral part of the landscape, these elements are apparently insufficient. Management to increase pollination services is therefore in need of urgent investigation.
Highlights
Global agriculture has become increasingly pollinator-dependent with a disproportionate increase in the area cultivated with pollinator-dependent crops [1]
It is vital to explore if the local pollinator community can support the expansion of pollinator-dependent crops, especially in developing countries. We address this gap by evaluating the pollen limitation and pollination success of a common oil crop with a manipulative experiment across a heterogeneous agricultural landscape in southwestern Ethiopia
We found severe pollen limitation across a heterogeneous agricultural landscape in southwestern Ethiopia, which we suggest to be linked to the low bee abundance found in the landscape
Summary
Global agriculture has become increasingly pollinator-dependent with a disproportionate increase in the area cultivated with pollinator-dependent crops [1]. We analysed the pollen limitation of rapeseed in relation to bee abundance and richness that we sampled with vane and pan traps in the same homegardens. On local pollinator communities and pollen limitation, we included weights (alpha) on the land-use variables to scale the impact of land use as a function of distance from the homegarden (equation (2.1)):. We thereafter analysed total number of seeds per plant, as a proxy for yield, in relation to forest cover in the surrounding landscape, altitude, flower abundance and the area of annual crop within one hectare plot with site as random effect. We evaluated if local bee abundance and richness affected the pollen limitation of the plants by adding one of the following variables to the final model: abundance of bees including honeybees, abundance of bees without honeybees and bee species richness, and included their interaction with treatment. We graphically evaluated all models by plotting the distribution of the residuals, the residual variation between treatments and the standardized residuals versus fitted values and versus each explanatory variable [32]
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