Flowering resources distract pollinators from crops: Model predictions from landscape simulations

Abstract

1. Enhancing floral resources is a widely accepted strategy for supporting wild bees and promoting crop pollination. Planning effective enhancements can be informed with pollination service models, but these models should capture the behavioural and spatial dynamics of service-providing organisms. Model predictions, and hence management recommendations, are likely to be sensitive to these dynamics.2. We used two established models of pollinator foraging to investigate whether habitat enhancement improves crop visitation; whether this effect is influenced by pollinator foraging distance and landscape pattern; and whether behavioural detail improves model predictions. 3. The more detailed central place foraging model better predicted variation in bee visitation observed between habitat types, because it includes optimized tradeoffs between patch quality and distance. Both models performed well when predicting visitation rates across broader scales. 4. Using real agricultural landscapes and simulating habitat enhancements, we show that additional floral resources can have diverging effects on predicted crop visitation. When only co-flowering resources were added, optimally foraging bees concentrated in enhancements to the detriment of crop pollination. For both models, adding nesting resources increased crop visitation. Finally, the marginal effect of enhancements was greater in simple landscapes. 5. Synthesis and applications. Model results help to identify the conditions under which habitat enhancements are most likely to increase pollination services in agriculture. Three design principles for pollinator habitat enhancement emerge: (a) enhancing only flowers can diminish services by distracting pollinators away from crops, (b) providing nesting resources is more likely to increase bee populations and crop visitation and (c) the benefit of enhancements will be greatest in landscapes that do not already contain abundant habitat. K E Y W O R D S agriculture, bees, central place foraging, ecosystem services, habitat enhancements, pollination, pollinator, pollinator habitat

The effectiveness of flower strips and hedgerows on pest control, pollination services and crop yield: a quantitative synthesis

“…The ‘exporter’ hypothesis (Morandin and Kremen, 2013; Kremen et al ., 2019) predicts enhanced delivery of ecosystem services through functional spillover from floral plantings ( sensu Blitzer et al ., 2012; Albrecht et al ., 2007; Morandin and Kremen, 2013; Pywell et al ., 2015; Tschumi et al ., 2015, 2016; Sutter et al ., 2017). However, according the ‘concentrator’ hypothesis (Kremen et al ., 2019; also referred to as the ‘aggregation’ hypothesis (Venturini et al ., 2017a) or the ‘Circe principle’ (Lander et al ., 2011)), resource‐rich floral plantings temporarily compete with flowering crops and concentrate pollinators and natural enemies from the surrounding agriculture into the floral plantings, potentially resulting in (transiently) reduced crop pollination and pest control services (Nicholson et al ., 2019). This may explain why plantings fail to enhance crop pollination or pest control services, even if they successfully promote local pollinator or natural enemy abundance in restored habitats (e.g.…”

Foraging distances in six species of solitary bees with body lengths of 6 to 15 mm, inferred from individual tagging, suggest 150 m-rule-of-thumb for flower strip distances

“…Increased flight requirements reduce adult lifespan (Schmid-Hempel and Wolf 1988), and absences from the nest increase brood cell parasitism, as parasites enter the nest while the nest owner is away (Seidelmann 2006). Proximity of nesting and foraging sites is therefore crucial for the reproductive success of bees, and we need more data on foraging distances to predict the effects of habitat enhancements for conservation purposes (Nicholson et al 2019).…”

Bee communities and pollination services in adjacent crop fields following flower removal in an invasive forest shrub

“…This suggests that L. maackii flowers were distracting many small species from the adjacent crop field, which should reduce pollination of nearby crops that co‐flower (Nicholson et al. ).…”