Plants establish pollination interactions with different groups of animals, including nocturnal ones that establish interactions with economically valuable and culturally important crops, as well as wild plants of conservation concern. Despite the considerable number of studies addressing the structure and dynamic of pollination networks, nocturnal interactions have been relatively overlooked. Using a multilayer network approach and considering diurnal and nocturnal interactions, we aimed to understand how interactions at different periods of the day are integrated and contribute to the network structural pattern. We also aimed to highlight how multilayer networks may give a more nuanced assessment of species importance across layers.

We assembled a pollination network of an intensively studied Neotropical area by standardizing interaction data from 16 previous studies into a presence/absence (binary) network. Then we used a multilayer network approach to evaluate the network modularity and plant species' roles in these different temporal layers. Plants were classified as nocturnal or diurnal according to the onset of floral opening and pollinators were classified according to their foraging period.

The network consisted of 178 pollinator species and 158 plant species, with 870 links. Among plant species, 135 species have diurnal floral opening while 23 species are nocturnal. The multilayer network was significantly modular, and these modules differed in the composition of pollinator groups (e.g., hawk moths, bats, bees, hummingbirds), as well as of diurnal and nocturnal plants. We show that diurnal and nocturnal interactions are organized into interconnected modules in the multilayer network. Nocturnal plants had higher values of versatility and multidegree than diurnal plants, due to their role in connecting the two temporal layers.

Synthesis. Our study highlights the importance of integrating different pollination systems to understand the importance of distinct components that structure pollination networks. We also illustrate the value of tapping into existing information, particularly species interaction data, from well studied biodiversity hotspot areas, to gain a better understanding of how communities are structured. Finally, despite the relative scarcity of nocturnal pollination network studies, we showed nocturnal plants, which often make complementary use of diurnal pollinators, to be important in connecting the temporal layers.

The plant-pollinator interactions analysed here were sampled at the Panga Ecological Station (PES), located around 40 km from the centre of Uberlândia city, state of Minas Gerais, Brazil (19.156° – 19.186° S and 48.389° – 48.410° W, altitude ≈ 800 m above sea level). The PES is a 405ha Private Reserve of Natural Heritage (IBAMA Ordinance N^o. 072/97 of June 4, 1997) that was created in 1986 by the Federal University of Uberlândia to carry out research in preserved Cerrado environments. It contains several types of vegetation typical of the Cerrado, a large Neotropical savanna ecosystem, including savanna, forest, and open grassland areas. Climate in the region shows two well defined seasons: one cooler and drier, between May and September; and a warmer and wetter period, from October to April.

We compiled all the known studies on plant-pollinator interactions conducted in the PES, carried out between 1990 and 2017, each focusing on distinct groups of plants and pollinators, using different sampling approaches most appropriate for each group, including focal observation or pollinators capture for pollen load identification. The information on plant-pollinator interactions were organized into a binary matrix, with pollinators in the columns and plants in the rows. Each cell was filled with 1 when an interaction between the pair of a plant and pollinator was recorded and 0 otherwise.