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1. Conservation in post‐industrial cities: How does vacant land management and landscape configuration influence urban bees?

   https://doi.org/10.1111/1365-2664.13773  

   Turo, Katherine J. ; Spring, MaLisa R. ; Sivakoff, Frances S. ; Delgado de la flor, Yvan A. ; Gardiner, Mary M. ; Garibaldi, ed., Lucas ( October 2020 , Journal of Applied Ecology)

   Rich pollinator assemblages are documented in some cities despite habitat fragmentation and degradation, suggesting that urban areas have potential as pollinator refuges. To inform urban bee conservation, we assessed local‐ and landscape‐scale drivers of bee community composition and foraging within vacant lots of Cleveland, Ohio, USA. Cleveland is a shrinking city, a type of urban area that has an over‐abundance of vacated greenspaces as a result of population loss and subsequent demolition of abandoned infrastructure. As such, Cleveland represents over 350 post‐industrial cities worldwide that are all promising locations for bee conservation.

   Across a network of 56 residential vacant lots (each ~30 m × 12 m), we established seven unique habitats, including seeded native prairies, to investigate how vegetation management and landscape context at a 1,500 m radius influenced urban bee communities. We assessed the distribution of several bee functional traits, diversity and abundance with pan and malaise traps. Foraging frequency was determined with plant–pollinator interaction networks derived from vacuum collections of bees at flowers.

   We observed higher bee richness and increased abundance of smaller sized bees as the size of surrounding greenspace patches increased within a 1,500 m radius landscape buffer. Within habitats, seeded treatments had no effect on bees but greater plant biomass and shorter vegetation were correlated with increased bee richness and abundance. Plant–pollinator interaction networks were dominated by spontaneous non‐native vegetation, illustrating that this forage supports urban bees.

   Synthesis and applications. Our study indicates that proximity to larger greenspaces within an urban landscape promotes overall bee richness and increased occurrence of smaller bee species within residential vacant lots. While we did not observe our seeded native plants enhancing the bee community, native wildflowers were still establishing during the study and may have a greater influence when blooming at higher densities. Importantly, spontaneous non‐native vegetation provided the majority of urban bee's forage. Thus, vacant land that is minimally managed and vegetated with what many consider undesirable ‘weeds’ provides valuable habitat for bee conservation in cities.

    

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2. Small but critical: semi-natural habitat fragments promote bee abundance in cotton agroecosystems across both Brazil and the United States

   https://doi.org/10.1007/s10980-019-00868-x  

   Cusser, Sarah ; Grando, Carolina ; Zucchi, Maria Imaculada ; López-Uribe, Margarita M. ; Pope, Nathaniel S. ; Ballare, Kimberly ; Luna-Lucena, Danielle ; Almeida, Eduardo A. ; Neff, John L. ; Young, Kenneth ; et al ( July 2019 , Landscape Ecology)

   Context Bees are the most important pollinators of crops worldwide. For most bees, patches of semi-natural habitat within or adjacent to crops can provide important nesting and food resources. Despite this, land cover change is rapidly reducing the abundance of semi-natural habitat within agroecological landscapes, with potentially negative consequences for bee communities and the services they provide. Objectives Identify how the availability of semi-natural habitat impacts bee communities across biogeographic regions, which may reveal commonalities and key governing principles that transcend a single region or taxa. Methods We analyze and compare the drivers of bee community composition in cotton fields within Brazil and the U.S. to reveal how land cover and land cover change impact bee community composition across these two regions. Results We show that the most critical factors impacting bee communities in cotton agroecosystems are the same in Brazil and the U.S.: bee abundance increases with cotton bloom density and the abundance of semi-natural habitat. Further, the loss of semi-natural habitat over a 5-year period negatively impacts bee abundance in both agroecosystems. Conclusions Given the importance of bee abundance for the provision of pollination service in cotton plants, our findings highlight the significance of small semi-natural habitat fragments in supporting key ecosystem service providers for both tropical and temperate cotton agroecological systems. We underscore the important role that local land managers play in biodiversity conservation, and the potential contribution they can make to pollination provision by supporting agricultural landscapes that conserve fragments of semi-natural habitat. 

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3. Multiscale habitat mediates pest reduction by birds in an intensive agricultural region

   https://doi.org/10.1002/ecs2.2884  

   Heath, Sacha K. ; Long, Rachael F. ( October 2019 , Ecosphere)

   Habitat augmentation on farms is predicted to conserve biological diversity and support beneficial animals that reduce crop pests. Effectiveness of local habitat enhancement and subsequent pest reduction services can be mediated by the amount of habitat at larger scales. We tested whether the presence and increase of local and landscape scale bird habitat increased avian predator abundance and pest reduction by birds. We surveyed birds and performed a sentinel prey exclosure experiment in walnut orchards in the Sacramento Valley, California,USA—comparing predation probability between orchards with (n = 10) and without (n = 10) woody habitat in uncultivated orchard margins. We digitized seminatural habitat cover in landscapes around orchards to test the effectiveness of avian predators in reducing sentinel prey along a seminatural cover gradient of 0–38%. Experimental prey were diapausing larvae ofCydia pomonella(L.) (Lepidoptera: Tortricidae; codling moth), a significant pest of walnuts, which overwinter in cocoons in orchards, emerge as adults, and produce larvae that feed on the nuts the following spring. Permitting bird access to cocoons increased larval predation from 11% (caged) to 46% (no cage), and predation increased with increasing proportions of seminatural habitat within 500‐m of orchard transects. Predation also increased as the size and bark furrow depth of walnut trees increased, likely because these characteristics were associated with increasing abundance of avian predators with functional traits specific to consuming tree‐dwelling cocoons (e.g., woodpeckers). The presence and increasing complexity of local margin habitat increased the species richness and abundance of avian predators but was not predictive of cocoon predation. Consistent with intermediate landscape‐complexity hypothesis predictions, the effect size of woodpecker abundance on predation was large in simple landscapes (1–20% seminatural cover) and low in complex landscapes (>20% cover). Contrary to predictions, effect size was large in cleared landscapes (<1% cover), suggesting that orchards supported predators in cleared landscapes, with positive effects on pest reduction. We provide evidence that increasing the abundance of avian predators with traits specific for consuming target pests—by retaining old trees and seminatural cover—can increase orchard pest reduction services in an intensive agricultural region.

    

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4. Not all matrix habitat is created equal for rare bee species in forest habitat

   https://doi.org/10.1111/een.13029  

   Volenec, Zoe M. ; Smith, Colleen M. ( March 2021 , Ecological Entomology)

   1. Anthropogenic land‐use change alters the ecological communities in a landscape's remaining natural habitat. These matrix effects are understudied in rare species, which comprise a majority of biodiversity, contribute to ecosystem services, and are particularly vulnerable to population declines.

   2. This study used bee species survey data from New Jersey forest fragments, in conjunction with an independent museum data set, to identify rare bee species and developed regularised regularised regression models of matrix effects on their richness and abundance.

   3. By using a regularised modelling approach, this study explains 44.43% of variation in rare bee species richness between forest fragments and 27.27% of variation in their abundance (average adjustedR²).

   4. The present study's results identified specific subcategories of urban land use in the surrounding 1000 m of forest fragments that explained patterns in rare bee species richness and abundance, providing insights into how to select forest fragments to conserve rare bees. Low priority should be given to fragments in close proximity to high‐ and medium‐density housing, which likely harms rare bees by increasing impervious surface cover. Low priority should also be given to fragments near golf courses and athletic fields; this study speculates that these land uses harm rare bees through mowing and pesticide application. Finally, high priority should be given to fragments composed of a larger proportion of mature forest, which likely provides a greater diversity of native floral resources. Altogether, this study's model results reveal the importance of matrix habitats for the biodiversity of rare species in forest fragments.

    

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

   https://doi.org/10.1111/1365-2664.13333  

   Nicholson, Charlie C. ; Ricketts, Taylor H. ; Koh, Insu ; Smith, Henrik G. ; Lonsdorf, Eric V. ; Olsson, Ola ; Requier, ed., Fabrice ( February 2019 , Journal of Applied Ecology)

   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.

   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.

   The more detailed central place foraging model better predicted variation in bee visitation observed between habitat types, because it includes optimized trade‐offs between patch quality and distance. Both models performed well when predicting visitation rates across broader scales.

   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.

   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.

    

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