No abstract

Biological communities are subject to spatiotemporal variations in community structure, i.e., species composition, richness, and abundance. Plant-pollinator interactions are affected by species composition and abundance, so that rapid changes in plant community structure can lead to critical impacts on plant-pollinator interactions at the community level. The extent of these impacts depends on how plants respond to different kinds of stressors, such as the disturbance caused by invading species. In this research, we conducted a before-and-after study to evaluate the potential effects of an invasive fast-growing alien grass species on the structure of a plant-pollinator interaction network. We described the changes in community structure and plant-pollinator interactions over two sampling periods, through the temporal β-diversity of plant and bee species, plant-bee interactions, and plant functional traits. Our results showed that changes in plant community composition (especially the plants in the network core) and decrease in plant species richness, as well as in floral resources availability impacted plant-pollinator interactions of a grassland community after the growth of a fast-growing alien grass species. These changes were accompanied by a decrease in plant-bee interaction diversity, and a high β-diversity of species interactions mainly due to interaction rewiring. However, we found no effect on the functional diversity of flowers. In conclusion, our study showed that a short-term change in plant species composition and floral resource abundance impacted plant-bee interactions, which markedly changed network structure and dynamics.

1. Plant–animal mutualisms are key processes that influence community structure, dynamics, and function. They reflect several neutral and niche‐based mechanisms related to plant–animal interactions.2. However, the strength with which these processes influence community structure depends on functional traits that influence the interactions between mutualistic partners. In mutualisms involving plants and ants, nectar is the most common reward, and traits such as quantity and quality can affect ant species' responses by influencing their recruitment rates and aggressiveness.3. In this study, nectar traits that mediate ant–plant defensive mutualisms were manipulated to test whether resource quantity and quality affect the structure of ant–plant interaction networks. A downscaling approach was used to investigate the interaction network between ant species and individual plants of the extrafloral nectary‐bearing terrestrial orchid Epidendrum secundum.4. We found a short‐term reorganization of the ant assemblage that caused the interaction networks to become more specialised and modular in response to a more rewarding nectar gradient. Furthermore, the ant species tended to narrow their foraging range by limiting their associations to one or a few individual plants.5. This study shows that ant species' responses to variable resource traits play an important role in the structure of the ant–plant interaction network. We suggest that more rewarding nectar enhanced aggressiveness and a massive recruitment of some ant species, leading to lower niche overlap and thus a less connected and more specialised network.

No abstract

Nectar is the most common floral resource that mediates plant-pollinator interactions, and its spatiotemporal distribution is related to pollinator attraction and can influence pollinator activity through time. Therefore, assessing patterns of floral phenology of nectar-producing plants can help better understand the pollinator assemblage's temporal dynamics. We used an area of afforested Brazilian Cerrado covered with a highdensity plantation of Inga vera, a mass-flowering nectar-producing tree, to investigate whether intra-seasonal and daily variations in nectar availability provided by I. vera flowers affect the bee assemblage. We showed that bee abundance was positively related to intra-seasonal patterns in floral phenology and daily changes in nectar production. Although bee species richness was also associated with intra-seasonal changes in nectar availability, bee diversity (quantified using Simpson's diversity index) did not follow the same pattern. We suggest that the dominance of the invasive honeybee, Apis mellifera, on I. vera flowers may have affected the overall bee diversity over time due to an exacerbated increase in honeybee abundance. Therefore, by evaluating the temporal dynamics of nectar availability, an important floral attribute that influences plant-pollinator interactions, we suggest that planting high-rewarding tree species at high densities in open ecosystems can affect the dynamics of native bee assemblages negatively due to the exacerbated recruitment of the dominant exotic honeybee.