Pollinator specialization increases with a decrease in a mass‐flowering plant in networks inferred from DNA metabarcoding

Abstract

How native mass‐flowering plants affect the specialization of insects at individual and species levels and the consequences for pollination networks have received much less attention than for mass‐flowering crops or alien species and basically remain unexplored. Using existing DNA metabarcoding data on the pollen loads of 402 flower‐visiting insects, we assessed the effects of a native mass‐flowering plant of high reward quality, the shrub Rhododendron ferrugineum, on pollination networks by investigating: (a) the food niches of individual pollinators and pollinator species and (b) the structure of individual and species networks in subalpine heathland patches with extremely contrasted densities of R. ferrugineum. Relative to its high abundance in high‐density patches, the shrub was greatly underrepresented and did not dominate individual's or species' generalized networks, rather individual and species specialization increased with a decrease in R. ferrugineum density. Furthermore, individuals of the more generalist dipteran Empididae species tended to extend exclusive interactions with rare plant species in low‐density networks. The same trend was observed in the more specialist Apidea but toward rare species in high‐density networks. Our results reveal a quite paradoxical view of pollination and a functional complementarity within networks. Niche and network indices mostly based on the occurrence of links showed that individual pollinators and pollinator species and networks were highly generalized, whereas indices of link strength revealed that species and above all individuals behave as quite strict specialists. Synthesis. Our study provides insights into the status of a native mass‐flowering plant in individual's and insect species' food niches and pollination networks. It revealed that a generalist pollinator species can be highly specialized at the individual level and how rare plant species coexisting with mass‐flowering plants may nevertheless be visited.

Plant biodiversity assessment through pollen DNA metabarcoding in Natura 2000 habitats (Italian Alps)

“…Within the common families, the taxonomic information resulting from the metabarcoding method was richer (27% more taxa) and provided a finer resolution (53% more genera) when compared to the light microscopy results. The observed improvement in taxonomic information is in agreement with previous studies 15 , 19 , 20 , 27 . In particular, for some taxa that are usually identified only collectively (at family level or higher) with conventional light microscopy (e.g.…”

“…This limitation to taxonomic precision can be tackled by the exploitation of the DNA-based approaches which recently revolutionized environmental monitoring 14 . Pollen DNA from environmental samples has been used in recent years as a matrix in different fields, including the study of airborne allergenic pollen 12 , 15 , 16 , plant–pollinator interactions 17 – 19 and provenance of honey 20 , 21 .…”

Introduced bees (Osmia cornifrons) collect pollen from both coevolved and novel host-plant species within their family-level phylogenetic preferences

“…Final filtering removed plant genera that were extremely rare in the dataset, those that contained less than 0.3% of the total counts per site across all sites. Because relative pollen abundances (RRA) by light microscopy and ITS2 metabarcoding have been previously strongly correlated with the primers applied here [33], we used RRA as a proxy for pollen abundance in larval provisions [38][39][40]. We analysed RRAs by site or landscape using the mean of RRAs from 12 samples per site and used RRAs as a population wide estimate of pollen use and not sample-wise abundance estimations [38,41,42] (see electronic supplementary material, table S1 for species list and metadata, and for raw data see https://doi.org/10.5061/dryad.ffbg79cqn).…”

Plant richness and blooming cover affect abundance of flower visitors and network structure in Colombian orchards

“…Alternatively, some deciduous fruit trees provide many flowers but poor resources in each flower (Díaz et al, 2013), requiring high pollinator abundance, and not just an efficient pollinator. In fact, some authors have reported that specialization decreases with an increase in mass-flowering plants, because specialized animals require high-quality resources (Pornon et al, 2019).…”