Pollination networks along the sea-inland gradient reveal landscape patterns of keystone plant species

Abstract

Linking the functional role of plants and pollinators in pollination networks to ecosystem functioning and resistance to perturbations can represent a valuable knowledge to implement sound conservation and monitoring programs. The aim of this study was to assess the resistance of pollination networks in coastal dune systems and to test whether pollination interactions have an explicit spatial configuration and whether this affect network resistance. To this aim, we placed six permanent 10 m-wide belt transects. Within each transect we placed five plots of 2 m x 2 m, in order to catch the different plant communities along the dune sequence. We monitored pollination interactions between plants and pollinators every 15 days during the overall flowering season. The resulting networks of pollination interactions showed a relatively low degree of resistance. However, they had a clear spatial configuration, with plant species differently contributing to the resistance of pollination networks occurring non-randomly from the seashore inland. Our results evidenced that beside contributing to the creation and maintenance of dune ridges, thereby protecting inland communities from environmental disturbance, plant species of drift line and shifting dune communities have also a crucial function in conferring resistance to coastal dune pollination networks.

Figure 1

Simplified representation of the physiognomy of coastal dune systems along the North Adriatic Coast. Plant communities were identified by different letters: (A) pioneer community of the drift line, (B) pioneer community of shifting dunes, (C) xerophilous grasslands of semi-fixed dunes, (D) interdunal depressions, (E) xerophilous shrublands of fixed dunes, (F) xerophilous woodlands of fixed dune. We gratefully acknowledge Miss Lara Dal Molin for the hand painted picture.

Figure 2

Accumulation curves of the richness of (a) animal-pollinated plants, (b) pollinators, and (c) pollination interactions. Accumulation curves were computed by using the cumulative number of plots sampled per plant community as the unit of sampling effort. Plant communities were represented by different colours: green pioneer community of the drift line, yellow pioneer community of shifting dunes, red xerophilous grasslands of semi-fixed dunes, violet xerophilous shrublands of fixed dunes, blue xerophilous woodlands of fixed dune.

Figure 3

Linear Mixed Models (LMM) between plots log-transformed distance from the sea and the richness of (a) animal-pollinated plant and (b) pollinator species. Lines represent the estimates of the models. Dots of different colours represent different plant communities: green pioneer community of the drift line, yellow pioneer community of shifting dunes, red xerophilous grasslands of semi-fixed dunes, violet xerophilous shrublands of fixed dunes, blue xerophilous woodlands of fixed dune.