Urbanization gradients influence both landscape and climate and provide opportunity for understanding how plants and pollinators respond to artificially driven environmental transitions, a relevant aspect for the ecosystem service of pollination. Here, we investigated several aspects of pollination along an urbanization gradient in landscape and climate. We quantified wild hoverfly and bee abundances with trapping, standing crop of nectar with spectrophotometer, and the pollen transported by flower visitors with DNA metabarcoding, in 40 independent sites from semi‐natural to built‐up areas in Northern Italy. Direct and indirect effects were fitted considering landscape and climate variables. Linear and nonlinear relationships were detected along the urbanization gradient. Pollinator abundances increased quadratically and peaked at 22% of impervious cover with an 81% growth, and they decreased with green‐patch distance by 37% and urban park largeness by 60%. This indicates that pollinators are more abundant at intermediate levels of urbanization. Climatically, pollinators diminished by up to 46% in areas with low spring–summer temperature seasonality: urban areas likely posing thermic stress. Furthermore, the sugar mass available in nectar increased by 61% with impervious cover and by 79% with precipitations, indicating that city nectars were less consumed or flowers more productive. Furthermore, the species richness of pollen decreased by 32% in highly urbanized areas, and contained a high incidence of exotic plants, hinting for anthropized, simplified plant communities. Synthesis and applications. Urbanization influences pollinator abundances, nectar resources and transported pollen in direct and indirect ways. Pollinators are negatively affected by a thermally harsh climate in highly urbanized areas with isolated green areas and large parks. Suburban landscapes demonstrated the highest pollinator presence. In the city core, flowers contained more nectary sugar in association with more precipitations, while pollinators collected pollen from a small number of plants, mainly exotic. These findings highlight the strong influence of urban landscape and climate on pollinators and plants, showing that cities are heterogenous realities. Patterns from this study will serve as basis for pollinator‐friendly planning, mitigation and management of urban landscapes.

Wildlife-friendly management practices promote pollinators and pollination services in agricultural landscapes. Wild bee densities are driven by landscape composition, as they benefit from an increased availability of nesting and foraging resources at landscape scale. However, effects of landscape composition on bee foraging decisions and consequences for crop pollination have rarely been studied. We investigated, how landscape composition affects bee densities and foraging behavior in faba bean (Vicia faba L.) fields and how this impacts faba bean yield. We recorded densities and nectar robbing behavior of honeybees, long- tongued and short-tongued bumblebees in faba bean fields in eleven landscapes with varying landscape composition (e.g. land cover of oilseed rape, faba bean and semi-natural habitats). Moreover, we assessed yield components of faba beans via pollinator exclusion experiments. Increasing covers of faba bean and semi-natural habitats positively influenced bumblebee densities, while high oilseed rape covers negatively affected short-tongued bumblebee densities in bean fields. Increased faba bean covers enhanced the proportion of nectar-robbing short-tongued bumblebees. The number of beans per pod was increased by insect pollination, while the number of pods was decreased; these effects however depended on variety. Landscape composition interacted with bee densities in shaping yield components in V. faba. Our study emphasizes the importance of considering landscape management to maximize crop yields, as shown for the case of faba beans. The composition of agricultural landscape can modulate bee densities in crop fields, bees` foraging behavior and pollination services.

Solitary bees are receiving increasing attention as they are very effective crop pollinators. However, widespread implementation of pollination management with solitary bees is hampered by a lack of targeted and practical guidelines. Indeed, little evidence-based guidelines exist about the preferred type of nesting material, how to control nest-associated macroparasites and how to promote a healthy offspring with sufficient female bees. This study investigated whether different types of artificial nesting materials – paper straws and wooden grooved boards – are preferred by the European orchard bee (Osmia cornuta). In addition, we explored how the bee nesting success and infestation of macroparasites are influenced by type of nesting material, landscape complexity and timing throughout the active nesting period of O. cornuta. We found that O. cornuta preferred to nest in paper straws compared to wooden grooved boards. The number of produced brood cells and the offspring sex-ratio (i.e. the ratio of female:male bees) were higher in wooden grooved boards. Number of brood cells, successful cocoon development and the sex-ratio all decreased throughout the nest-construction period of the bees. The sex-ratio also increased with increasing landscape complexity. Paper straws had a reduced infestation rate of kleptoparasitic mites. In addition, the infestation rate of both kleptoparasitic mites and kleptoparasitic drosophilid flies increased with time throughout the bees' nest-construction period. These findings present relevant evidence to aid successful implementation of solitary bees for crop pollination. Utilization of paper straws, or similar materials, over wooden grooved boards and closing the nests near the end of the bees’ active nest-construction period should be recommended practices. Implementation of these practices will reduce parasite infestation and enhance bee nesting success. Furthermore, conservation of semi-natural habitat or planting pollinator-friendly vegetation around fields is also advised to promote the proportion of female bees in the offspring.

Urbanization is a primary threat to biodiversity and the functioning of both natural and agro-ecosystems. Especially in the Global South, expanding cities increasingly encroach fertile agricultural lands, questioning the viability of maintaining agricultural activities in urbanized landscapes. Yet, the growing interest in urban agriculture may offer an opportunity to improve the sustainability of cities. Indeed, urban agriculture often consists in small-scale wildlife-friendly farming, and thus can provide resources and habitats for various organisms, while locally producing food within and around cities. However, the effects of urbanization on agricultural biodiversity and the delivery of ecosystem services upon which urban smallholders depend such as biological pest control and crop pollination are little understood, especially in global urbanization hot spots from the tropics. This thesis is part of a larger interdisciplinary and collaborative research project between Germany and India that aims to investigate how urbanization affects urban agriculture. This project takes place in Bengaluru, an emerging megacity in South India, which exemplifies key characteristics of urbanization and serves as an in situ laboratory to assess their effects on agro-ecological and socio-economic attributes of urban agriculture. Within the project, this thesis focuses on agricultural biodiversity and associated services across rural-urban landscapes. The thesis is divided into four chapters. The first three chapters investigate how urbanization drives the spatial and temporal dynamics of service-providing organisms, namely birds and bees. Going one-step further, the fourth chapter, as a case study, looks at how urbanization affects the delivery of pollination service to mango, one of the most important tropical fruit crops. Chapter 1 reports on the drivers of taxonomic and functional beta-diversity of farmland birds along an urbanization gradient. This chapter demonstrates that urbanization acts as an environmental filter and homogenizes farmland bird communities, and discusses the potential implications for ecosystem services. Chapter 2 focuses on the functional responses of farmland bees to urbanization, and how urban farm characteristics can modulate these responses. It emphasizes how some functional groups of bees thrive in urban landscapes while others suffer, and how results from studies conducted in tropical countries do not necessarily align with that of studies from temperate regions. It also highlights how certain urban agricultural practices, such as crop diversification or flowering field margins, can promote bee communities. Chapter 3 provides novel insights on an understudied topic, namely the effects of urbanization on spatial and temporal dynamics of plant-pollinator interaction networks. The results show that urbanization alters the spatiotemporal dynamics of plant-pollinator networks, by amplifying the seasonal turnover of their interactions. This study demonstrates that environmental, spatial, and temporal gradients interact to shape the dynamics of plant-pollinator networks. Finally, Chapter 4 serves as an example on how the direct and indirect effects of urbanization and farm management influence the delivery of ecosystem services, using mango production (Mangifera indica) as a case study. The results indicate that mango production can be maintained at a profitable level in urbanized landscapes with insect pollinators more than tripling final yield. However, insecticides applications had negative effects on insect pollinators, in turn reducing mango yield. This suggests a trade-off between conventional pest control and mango pollination. In conclusion, this thesis displays the variable effects of urbanization on the diversity of different animal groups and related ecosystem services. Whereas farmland bird communities homogenize with growing urban areas, the response of farmland bees varies largely among taxonomic and functional groups. This thesis also emphasizes when the findings align or differ between studies conducted in tropical vs temperate regions, and highlights that generalizations drawn from studies conducted in one region do not necessarily apply to the other. Further, our result suggests that urban farming can be maintained at a profitable level, at least in low intensity level urbanized landscapes. Finally, this work suggests that small-scale urban agriculture, if managed in a sustainable way, might be a promising strategy to reconcile biodiversity conservation and food production within and around cities, thus increasing their sustainability. | 2024-07-25