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?