3.2 Pollen DNA metabarcoding and plant-pollinator interactions
Pollen DNA metabarcoding yielded interactions between the collected insects and 112 plant taxa. Among these, 81 (72.3%) were assigned at species level, 28 (25%) at genus level, and 3 (2.7%) at family level. Plant taxa found in the overall pollen transported by insects on each island ranged between 9 and 58 (mean 26.4 ± 16.7), while the mean number of pollen plant taxa transported by each sampled insect was 3.5 ± 2.1. In plant-pollinator networks constructed from the DNA metabarcoding data, the Connectance index resulted significantly and negatively associated with the Edge density (Fig 2 b) and network size (Table 1). Individual pollinator degree resulted significantly, positively related to the Edge density. However, the responses of different insect species among the widespread and most abundant ones were not homogeneous in this case, as the values of this index significantly increased in the biggest bee Xylocopa fenestrata ( βi = 14.9 ; p = 0.001), while it was not significant in the case of the two smaller bees: Lasioglossum albescens ( βi = 2.94 ; p = 0.52) and Braunsapis picitarsis( βi = -6.02; p = 0.24) (Fig 3).
[Fig. 2]
[Fig. 3]
[Table 1]