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Sunflower (Helianthus annuus) pollination in California's Central Valley is limited by native bee nest site location
The delivery of ecosystem services by mobile organisms depends on the distribution of those organisms, which is, in turn, affected by resources at local and landscape scales. Pollinatorâdependent crops rely on mobile animals like bees for crop production, and the spatial relationship between flora...
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Published in: | Ecological applications 2016-03, Vol.26 (2), p.438-447 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | The delivery of ecosystem services by mobile organisms depends on the distribution of those organisms, which is, in turn, affected by resources at local and landscape scales. Pollinatorâdependent crops rely on mobile animals like bees for crop production, and the spatial relationship between floral resources and nest location for these centralâplace foragers influences the delivery of pollination services. Current models that map pollination coverage in agricultural regions utilize landscapeâlevel estimates of floral availability and nesting incidence inferred from expert opinion, rather than direct assessments. Foraging distance is often derived from proxies of bee body size, rather than direct measurements of foraging that account for behavioral responses to floral resource type and distribution. The lack of direct measurements of nesting incidence and foraging distances may lead to inaccurate mapping of pollination services. We examined the role of localâscale floral resource presence from hedgerow plantings on nest incidence of groundânesting bees in field margins and within monoculture, conventionally managed sunflower fields in California's Central Valley. We tracked bee movement into fields using fluorescent powder. We then used these data to simulate the distribution of pollination services within a crop field. Contrary to expert opinion, we found that groundânesting native bees nested both in fields and edges, though nesting rates declined with distance into field. Further, we detected no effect of fieldâmargin floral enhancements on nesting. We found evidence of an exponential decay rate of bee movement into fields, indicating that foraging predominantly occurred in less than 1% of mediumâsized bees' predicted typical foraging range. Although we found native bees nesting within agricultural fields, their restricted foraging movements likely centralize pollination near nest sites. Our data thus predict a heterogeneous distribution of pollination services within sunflower fields, with edges receiving higher coverage than field centers. To generate more accurate maps of services, we advocate directly measuring the autecology of ecosystem service providers, which vary by crop system, pollinator species, and region. Improving estimates of the factors affecting pollinator populations can increase the accuracy of pollination service maps and help clarify the influence of farming practices on wild bees occurring in agricultural landscapes |
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ISSN: | 1051-0761 1939-5582 |
DOI: | 10.1890/15-0033 |