The Plant-pollinator Bipartite And Its Formation Mechanism In The Zoige Alpine Meadow

Food webs,as an integration of interlinked trophic relationships,are a product of the evolution and adaptation of ecological systems and also an important factor affecting the structure and function of ecosystems.In recent years,the advances in computer technology and network analysis have greatly enhanced the level of network structure studies.As the typical representative of mutual bipartite networks,pollination networks are considered to have a highly nested architecture,in which the partners of specialists is a subset of generalists.The formation of the nested structure is mostly attributed to four processes,namely the neutral process concerning species relative abundance,the niche process concerning species traits,the phenology concerning temporal match for interaction and the phylogeny concerning species evolutionary history.However,none of previous studies has concurrently examined the effects of four processes in a single investigation,let alone evaluating the relative contribution of the four processes in a mutualistic network.In this study,I investigated the relative abundance and phenology for both pollinators and plants,and measured the floral characteristics and the pollinator size,as well as the phylogeny for both plants and pollinators using DNA barcoding for two years in an alpine meadow,Northwest Sichuan.My aim was to 1)construct a quantitative plant-pollinator bipartite and analyze its structure characteristics,and 2)explore the relative contribution of the niche process,neutral process,phenological match and species evolutionary history to structuring the bipartite.The study results are shown as follows:1.The plant-pollinator bipartite included 54 plant species belonging to 17 families and 80 animal species belonging to 47 families,among which 906 species interactions were observed.Flies,as an insect species group,visited the greatest number of plant species,reaching 32 and 39 in 2016 and 2017,respectively.At the species level,bees visited the greatest number of plant species(22 in 2016 and 34 in 2017).The Compositae species were the most generalized plants,receiving visitations from.41 and 65 pollinator species and showing strong interaction strength(48.33%and 49.62%)in 2016 and 2017,respectively.2.The plant-pollinator bipartite showed a nested architecture,with the calculated nestedness being 9.61 and 13.70 in 2016 and 2017,significantly lower than the confidence interval of 5%-95%predicted by the random model(56.42-67.69)and(62.39-71.21).Most of the species were generalists interacting with 2 to 5 partner species,and few interacted with more than 25 partner species.The partner species number per species on average was 4.3 and 6.0 in 2016 and 2017,respectively,and the connectance was about 0.2 in both years.3.For the number of partners per plant species,phenological match and niche process in 2016 explained 31.27%and 27.27%,respectively,whereas neutral process and evolutionary history were non-significant.Phenological match,niche process and neutral process explained 34.76%,31.73%and 16.78%,respectively,and the evolutionary history was non-significant in 2017.For the interaction frequency,niche process,neutral process,phenological match and evolutionary history in 2016 explained 38.47%,9.8%,7.92%and 0.6%,while in 2017 they explained 27.41%,27.91%,15.63%and 3.74%of the variation,respectively.4.Phenological match,neutral process,niche process,and evolutionary history in 2016 explained 23.96%,22.61%,10.22%and 6.06%of the variation in the number of partners per pollinator species,and 29.03%,31.89%,6.27%and 8.92%in the pollinator visitation frequency,respectively.In 2017,they explained 15.11%and 47.71%,9.38%and 1.45%in the number of partners per pollinator species,and 26.82%,32.01%,12.06%and 2.54%in pollinator visitation frequency,respectively.5.The information mechasim of the pollination network structure changed with year.The species evolutionary history in 2016,as well as the combination of neutral process and phenological match in 2017,was demonstrated to be the driver of network structure.In conclusion,our results show that the plant-pollinator bipartite was highly nested,regardless of the variation in species diversity between the study years,and this nested structure was due to phenological match,niche process,neutral process,and evolutionary history.However,their relative contribution to the network formation varied with the structural parameters and with the study year.Future studies should focus more on what contribute to the formation of species pairwise interaction and why the network is nested independent of the change in biological community.