Data from: Temporal variation in plant-pollinator networks from seasonal tropical environments: higher specialization when resources are scarce

The temporal dynamics of plant phenology and pollinator abundance across seasons should influence the structure of plant-pollinator interaction networks. Nevertheless, such dynamics are seldom considered, especially for diverse tropical networks. Here, we evaluated the temporal variation of four plant-pollinator networks in two seasonal ecosystems in Central Brazil (Cerrado and Pantanal). Data were gathered on a monthly basis over one year for each network. We characterized seasonal and temporal shifts in plant-pollinator interactions, using temporally discrete networks. We predicted that the greater floral availability in the rainy season would allow for finer partitioning of the floral niche by the pollinators, i.e., higher specialization patterns as previously described across large spatial gradients. Contrary to these expectations, we found that dry season networks, although characterized by lower floral resource richness and abundance, showed higher levels of network-wide interaction partitioning (complementary specialization and modularity). For nestedness and species level indices, though, this between-seasons difference was not consistent. Reduced resource availability in the dry season may promote higher interspecific competition among pollinators leading to reduced niche overlap, thus explaining the increase in specialization. Importantly, we also show that targeted data collection during peak flowering generates higher estimates of network specialization. Hence, depending on the period of data collection, different structural values for the networks of interactions may be found. Synthesis: Our study suggests that networks of tropical environments have structural properties that vary according to seasons, which should be taken into account in the description of the complex systems of interactions between plants and their pollinators in these areas.植物物候（plant phenology）与传粉者丰度（pollinator abundance）随季节变化的时间动态，理应影响植物-传粉者互作网络（plant-pollinator interaction networks）的结构。然而此类动态却极少被纳入研究考量，对于物种丰富的热带网络（tropical networks）而言更是如此。本研究针对巴西中部两类季节性生态系统——塞拉多（Cerrado）与潘塔纳尔（Pantanal）中的4个植物-传粉者互作网络，评估了其时间变异特征。每个网络均以月度为采样间隔，开展了为期一年的数据采集工作。我们通过构建时间离散化网络，刻画了植物-传粉者互作的季节与时间更替特征。我们曾提出假说：雨季更为充足的花卉资源，将促使传粉者对花生态位（floral niche）进行更精细的划分，即如既往大空间梯度研究中所报道的那样，呈现更高水平的特化模式。但与该假说预期相悖的是，尽管旱季的花卉资源丰富度与丰度均较低，其网络水平的互作划分程度——包括互补特化（complementary specialization）与模块化（modularity）——反而更高。不过就嵌套性（nestedness）与物种水平指标而言，季节间的差异并不具备一致性。旱季可利用资源的匮乏，可能会加剧传粉者间的种间竞争（interspecific competition），进而降低生态位重叠（niche overlap），这或可解释特化程度上升的原因。值得注意的是，我们还发现，在盛花期开展针对性的数据采集，会得到更高的网络特化评估结果。因此，数据采集的时段不同，所测得的互作网络结构参数也可能存在差异。综合与结论：本研究表明，热带环境下的互作网络，其结构属性会随季节发生变化。在描述这些区域植物与传粉者间复杂的互作系统时，应当将这一季节变异因素纳入考量。