Flexible foraging shapes the topology of plant–pollinator interaction networks

Abstract

In plant-pollinator networks, foraging choices by pollinators help form the connecting links between species. Flexible foraging should therefore play an important role in defining network topology. Factors such as morphological trait complementarity limit a pollinator's pool of potential floral resources, but which potential resource species are actually utilized at a location depends on local environmental and ecological context. Pollinators can be highly flexible foragers, but the effect of this flexibility on network topology remains unclear. To understand how flexible foraging affects network topology, we examined differences between sets of locally realized interactions and corresponding sets of potential interactions within 25 weighted plant-pollinator networks in two different regions of the United States. We examined two possible mechanisms for flexible foraging effects on realized networks: (1) preferential targeting of higher-density plant resources, which should increase network nestedness, and (2) context-dependent resource partitioning driven by interspecific competition, which should increase modularity and complementary specialization. We found that flexible foraging has strong effects on realized network topology. Realized connectance was much lower than connectance based on potential interactions, indicating a local narrowing of diet breadth. Moreover, the foraging choices pollinators made, which particular plant species to visit and at what rates, resulted in networks that were significantly less nested and significantly more modular and specialized than their corresponding networks of potential interactions. Preferentially foraging on locally abundant resources was not a strong driver of the realization of potential interactions. However, the degree of modularity and complementary specialization both increased with the number of competing pollinator species and with niche availability. We therefore conclude that flexible foraging affects realized network topology more strongly through resource partitioning than through focusing on high-density resources.

Massively Introduced Managed Species and Their Consequences for Plant–Pollinator Interactions

“…This high abundance argues in favour of some characteristics of networks. We have evidence that species density or biomass is correlated with several structural properties like generalism (Sauve et al, 2016;Spiesman and Gratton, 2016) through pollinator rewiring capacities or higher encounter probabilities (Fort et al, 2016). A recent study suggests that oilseed rape is central in plant-pollinator networks in crop fields when it is flowering (Stanley, 2013).…”

“…Yet, both insect and plant MIMS can interact with other wild species, rearrange pollination networks at the landscape scale (Spiesman and Gratton, 2016), and either facilitate or impair interactions with coflowering wild plant communities .…”

“…For example, in oilseed rape (MFC), a single field provides 350,000-700,000 plants per hectare, each producing more than 100 flowers (Hoyle et al, 2007) during a flowering period of about 4 weeks. This huge, temporary peak of resources available to pollinators can entirely rearrange pollination networks at the landscape scale (Spiesman and Gratton, 2016), and either facilitate or impair pollination networks with coflowering wild plant communities .Thus, it may indirectly influence a coflowering plant reproduction via the modification of shared pollinators foraging activity (Carvalheiro et al, 2014).…”

Partitioning wild bee and hoverfly contributions to plant–pollinator network structure in fragmented habitats

“…Accordingly, the strongest contribution of wild bees to network structure is “filling the gaps” in interaction matrices by shifting to alternative flower resources when pollinator diversity is high (Fründ et al. , Spiesman and Gratton ). This interspecific competition among pollinator groups is important for interaction network structuring toward robustness during community assembly (Bastolla et al.…”

Primate Infectious Disease Ecology: Insights and Future Directions at the Human-Macaque Interface

“…Bipartite and multimodal networks, which establish connections between different interlinked components of a system, may prove especially useful in this regard (Dormann et al 2017;Kane and Alavi 2008;Latapy et al 2008;Finn et al 2019). Recently, bipartite networks are beginning to feature in ecological and evolutionary research (reviewed in Bascompte and Jordano 2014;Cagnolo et al 2011;Dormann et al 2017), as illustrated by their being used to model marine food webs (Rezende et al 2009), mutualistic interactions between flowers and seed-dispersing animal pollinators (Spiesman and Gratton 2016;Stang et al 2009;Vazquez et al 2009), and, more pertinently, host-parasitoid relationships (Laliberte and Tylianakis 2010;Poulin et al 2013). For networks that combine links both within and across system components, some researchers have coined the term "multimodal networks," aka "multilayer" or "multislice networks" (Kane and Alavi 2008;Finn et al 2019).…”