An empirical attack tolerance test alters the structure and species richness of plant-pollinator networks

Usage NotesWhen using this dataset, please do include the citation of the orginal papers in the main text of your published article where these data are used. Thanks for understanding.ContentPlant-pollinator networks across the experimental manipulation (see below)Abstract1. Ecological network theory hypothesizes that the structuring of species interactions can convey stability to the system. Investigating how these structures react to species loss is fundamental for understanding network disassembly or their robustness. However, this topic has mainly been studied in-silico so far.2. Here, in an experimental manipulation, we sequentially removed four generalist plants from real plant-pollinator networks. We explored the effects on, and drivers of, species and interaction disappearance, network structure and interaction rewiring. Firstly, we compared both the local extinctions of species and interactions and the observed network indices with those expected from three co-extinction models. Secondly, we investigated the trends in network indices and rewiring rate after plant removal and the pollinator tendency at establishing novel links in relation to their proportional visitation to the removed plants. Furthermore, we explored the underlying drivers of network assembly with probability matrices based on ecological traits.3. Our results indicate that the cumulative local extinctions of species and interactions increased faster with generalist plant loss than what was expected by co-extinction models, which predicted the survival or disappearance of many species incorrectly, and the observed network indices were lowly correlated to those predicted by co-extinction models. Furthermore, the real networks reacted in complex ways to plant removal. Firstly, network nestedness decreased and modularity increased. Secondly, although species abundance was a main assembly rule, opportunistic random interactions and structural unpredictability emerged as plants were removed. Both these reactions could indicate network instability and fragility. Other results showed network reorganization, as rewiring rate was high and asymmetries between network levels emerged as plants increased their centrality. Moreover, the generalist pollinators that had frequently visited both the plants targeted of removal and the non-target plants tended to establish novel links more than who either had only visited the removal plants or avoided to do so.4. With the experimental manipulation of real networks, our study shows that despite their reorganizational ability, plant-pollinator networks changed towards a more fragile state when generalist plants are lost.MethodsThe study included three treatment and one control sites, located at a mean distance of 2.01±0.95 km from each other (treatments: 48°49’26.8”N-14°16’26.2”E; 48°49’51.63”N-14°17’34.12”E; 48°49’35.07”N-14°18’8.2”E; control: 48°49’26.8”N-14°16’26.2”E). Each site was a small grassland with a barrier of trees (see details in Biella et al. 2019 Scientific Reports). The experiment consisted of sequentially removing all inflorescences of the most generalist plant species from the entire surface of the treatment sites, one species at a time until four species were removed. We sampled flower-visiting insects in six 10m x 1m transects per site during two days for each experimental phase (before and after each species was removed), and synchronously in the control site. We identified all insects to species where possible, otherwise morpho-species were used when necessary (after pre-sorting into families and genera). In addition, we counted the number of flowers or inflorescences of all plant species within transects over the sampling period. article DOI: https://doi.org/10.1111/1365- 2435.13642 and a related study: https://doi.org/10.1038/s41598-019-43553-4<br>