Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades.

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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.

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