Most plant-pollinator networks are based on observations of contact between an insect and a flower in the field. Despite significant sampling efforts, some links are easier to report, while others remain unobserved. Therefore, visit-based networks represent a subsample of possible interactions in which the ignored part is variable. Pollen is a natural marker of insect visits to flowers. The identification of pollen found on insect bodies can be used as an alternative method to study plant-pollinator interactions, with a potentially lower risk of bias than the observation of visits, since it increases the number of interactions in the network. Here we compare plant-pollinator networks constructed (i) from direct observation of pollinator visits and (ii) from identification of pollen found on the same insects. We focused on three calcareous grasslands in France, with different plant and pollinator species diversities. Since pollen identification always yields richer, more connected networks, we focused our comparisons on sampling bias at equal network connectance. To do so, we first compared network structures with an analysis of latent blocks and motifs. We then compared species roles between both types of networks with an analysis of specialization and species positions within motifs. Our results suggest that the sampling from observations of insect visits does not lead to the construction of a network intrinsically different from the one obtained using pollen found on insect bodies, at least when field sampling strives to be exhaustive. Most of the significant differences are found at the species level, not at the network structure level, with singleton species accounting for a respectable fraction of these differences. Overall, this suggests that recording plant-pollinator interactions from pollinator visit observation does not provide a biased picture of the network structure, regardless of species richness; however, it provided less information on species roles than the pollen-based network.

大多数植物传粉媒介网络都是基于田间昆虫与花朵之间接触的观察结果。尽管进行了大量采样工作，但某些链接更易于报告，而其他链接则未被发现。因此，基于访问的网络代表了可能交互的子样本，其中被忽略的部分是可变的。花粉是昆虫到花的天然标志。鉴定昆虫体上的花粉可以用作研究植物与传粉媒介相互作用的一种替代方法，与访问观察相比，其偏倚风险可能更低，因为它增加了网络中相互作用的数量。在这里，我们比较了（i）直接观察授粉媒介访问和（ii）鉴定相同昆虫的花粉而构建的植物-传粉媒介网络。我们重点研究了法国三个钙质草原，它们的植物和传粉媒介物种多样性不同。由于花粉鉴定始终可以产生更丰富，连接更多的网络，因此我们将比较的重点放在网络连接相等的采样偏差上。为此，我们首先将网络结构与潜在块和图案的分析进行了比较。然后，我们通过分析主题中的专业化和物种位置，比较了两种类型网络之间的物种角色。我们的研究结果表明，至少在田间采样力求穷尽时，从昆虫访问的观察中采样不会导致网络的本质上与使用昆虫体上的花粉获得的网络不同。大多数显着差异是在物种级别而非网络结构级别发现的，单身物种占这些差异的可观比例。总体而言，这表明无论授粉媒介是否丰富，从授粉媒介访视观察中记录植物与授粉媒介的相互作用都不会提供网络结构的偏见。但是，它提供的物种角色信息少于基于花粉的网络。