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Background Landscape composition is known to affect both beneficial insect and pest communities on crop fields. Landscape composition therefore can impact ecosystem (dis)services provided by insects to crops. Though landscape effects on ecosystem service providers have been studied in large-scale agriculture in temperate regions, there is a lack of representation of tropical smallholder agriculture within this field of study, especially in sub-Sahara Africa. Legume crops can provide important food security and soil improvement benefits to vulnerable agriculturalists. However, legumes are dependent on pollinating insects, particularly bees (Hymenoptera: Apiformes) for production and are vulnerable to pests. We selected 10 pigeon pea (Fabaceae: Cajunus cajan (L.)) fields in Malawi with varying proportions of semi-natural habitat and agricultural area within a 1 km radius to study: (1) how the proportion of semi-natural habitat and agricultural area affects the abundance and richness of bees and abundance of florivorous blister beetles (Coleoptera: Melloidae ), (2) if the proportion of flowers damaged and fruit set difference between open and bagged flowers are correlated with the proportion of semi-natural habitat or agricultural area and (3) if pigeon pea fruit set difference between open and bagged flowers in these landscapes was constrained by pest damage or improved by bee visitation. Methods We performed three, ten-minute, 15 m, transects per field to assess blister beetle abundance and bee abundance and richness. Bees were captured and identified to (morpho)species. We assessed the proportion of flowers damaged by beetles during the flowering period. We performed a pollinator and pest exclusion experiment on 15 plants per field to assess whether fruit set was pollinator limited or constrained by pests. Results In our study, bee abundance was higher in areas with proportionally more agricultural area surrounding the fields. This effect was mostly driven by an increase in honeybees. Bee richness and beetle abundances were not affected by landscape characteristics, nor was flower damage or fruit set difference between bagged and open flowers. We did not observe a positive effect of bee density or richness, nor a negative effect of florivory, on fruit set difference. Discussion In our study area, pigeon pea flowers relatively late—well into the dry season. This could explain why we observe higher densities of bees in areas dominated by agriculture rather than in areas with more semi-natural habitat where resources for bees during this time of the year are scarce. Therefore, late flowering legumes may be an important food resource for bees during a period of scarcity in the seasonal tropics. The differences in patterns between our study and those conducted in temperate regions highlight the need for landscape-scale studies in areas outside the temperate region.
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Plant Communities in the Americas Are Highly Bee Dependent Regardless of Biome or Local Bee Diversity
ABSTRACT AimAll bees depend on angiosperms for survival, while many angiosperms depend on bees for reproduction. However, bee and flowering plant species richness do not peak in the same geographical regions of the world, suggesting that the flora in regions where bees are not as diverse, such as the tropics, may be relatively less bee‐dependent. We test this assumption by analysing whether local relative bee diversity can predict the proportion of angiosperm species that attract bees (i.e., “bee flowers”). LocationThe Americas. Time PeriodPresent. Major Taxa StudiedBees and angiosperms. MethodsWe map the proportion of bees to angiosperm species using recently available datasets of geographic distribution for both taxa. We then combine data from surveys on pollination systems for 56 floristic communities to estimate the proportion of angiosperm species with bee flowers in different regions. Finally, we test whether the proportion of bee flowers in a community can be predicted by a combination of relative bee species richness and abiotic environmental variables. ResultsBroad distribution maps show that the relative richness of bees in relation to angiosperms decreases in tropical areas; however, there is no evidence that tropical floristic communities are less dependent on bees. Interestingly, the proportion of angiosperm species with bee flowers was almost always found to be around 50% across biomes, with some variation depending on the habitat type and method of data collection. Main ConclusionsOur results suggest that plant communities can be highly bee‐dependent even where bees are relatively less diverse. While lower species richness does not mean lower abundance, and fewer bee species of specific life histories can still provide adequate pollination supply for a large number of angiosperm species, this pattern may impact how bee flowers interact with bees in different areas, and consequently how bees and bee flower specialisations have evolved over time.
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- Award ID(s):
- 2102006
- PAR ID:
- 10649892
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Global Ecology and Biogeography
- Volume:
- 34
- Issue:
- 8
- ISSN:
- 1466-822X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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