Introduction
Quantifying pollinator community responses to changes in land-use is essential because both wild and managed species provide critical pollination services to plants in natural and modified landscapes (Kleinet al. 2007; Winfree, Bartomeus & Cariveau 2011; Garibaldiet al. 2013; Rader et al. 2016). While many studies indicate that several ecosystem functions and/or services are at risk from land-use change and intensification (Kremen et al. 2002; Potts et al. 2010), responses of individual organisms to different land-use types are often variable (Bommarco et al.2010; Cariveau et al. 2013; Rader et al. 2014; Stavertet al. 2017). This makes it difficult to detect and understand how both plant and pollinator communities respond to land-use change. To date, most studies of pollinator community responses to changes in land-use intensity have focused on species-level relationships with the amount or proximity to natural and semi-natural vegetation (Greenleaf & Kremen 2006; Banks et al. 2013; Holzschuh et al. 2016; Hall et al. 2019).
The responses of pollinator species to land-use intensity are dependent on a number of factors including body size, social structure, nesting requirements, feeding behaviour and larval food availability (Henleet al. 2004; Rader et al. 2014; Hall et al. 2019). However, pollinator community composition is also directly influenced by changes in the availability of resources in space and time (Winfree & Kremen 2009). Different land-use types vary in the quantity and quality of resources, shaping use of these environments by pollinators based on if they are able to exploit available resources. For example, diverse bee communities are maintained by heterogeneous adjacent habitats that provide diverse food and nesting resources throughout the season (Winfree et al. 2011), while hover fly abundance and richness are dependent on food resources available for larval development, as well as habitat connectivity within landscapes (Power & Stout 2011; Haenkeet al. 2014). These landscape attributes ultimately affect which plant-pollinator interactions occur, where they occur, and how frequently.
In agricultural landscapes, knowledge of how plant-pollinator interactions change across land-uses is essential to understand the effects of intensive land management on the composition and performance of pollinator communities within the landscape. Understanding which floral resources are used by different taxa enables identification of agriculturally and ecologically important pollinators, as well as potential management actions to enhance the provision of pollination services. While linking the frequency of visits by pollinators to different plants at a particular site is the basic principle of plant-pollinator network studies (Memmott 1999), the connection between species and sites via species-habitat networks (sensu Mariniet al. 2019) allows for a landscape-scale view of species-habitat dependencies. This is important to inform conservation and management priorities by identifying keystone pollinator species or habitats that are critical for network structure (Saunders & Rader 2019). Here, we build on this approach by connecting traditional pollen transport networks (e.g. Alarcón 2010; Popic, Wardle & Davila 2013) with the land-uses in which they originate to generate a plant pollinator interaction-site bipartite network. This novel approach enables identification of key sites and land-uses with high plant-pollinator interaction diversity. Specifically, we ask:
1. How does land use intensity influence the proportion of insect taxa that are carrying pollen and the taxonomic richness of pollen they carry?
2. How do richness, uniqueness and strength of plant-pollinator interactions respond to the spatial scale of the surrounding land-use (field or landscape-scale)?
3. Which plant-pollinator interactions are likely to have high conservation value (i.e. keystone interactions) within and between land-use types?