Ecological Interaction Networks Between Bird And Rhododendron Plants In The Alpine Environment Of Mt. Gaoligong

Pollination network are an important indicator for assessing ecosystem stability and understanding ecological processes.Passerine birds play an important role in pollination system for the high-altitude Rhododendron plants,meanwhile,Rhododendron plants also provide remuneration for birds.However,the interactions between Rhododendron species and pollinators in the alpine region and its formation mechanism of the network structure are still unclear.Therefore,we studied ecological network of avian pollinators and Rhododendron plants at the community level,aiming to construct a pollination network and explore its features.Fieldworks were conducted at Pianma Pass of Mt.Gaoligong,Eastern Himalaya in the breeding seasons of 2017 and 2018.Recording 8 Rhododendron plants by the sympatric species and overlapping flowering time at high-altitude alpine environments(3026–3400 m).And field observations on Rhododendron plants and birds were video-taped GoPro cameras,we quantified the flowering plant-bird network with 100 h for each Rhododendron species,and we recorded all visits to the flowering Rhododendron plants visited by birds using focal plant watches during 2-3h blocks.The abundance of the birds and flowering Rhododendron species were investigated by the variable-radius point counts and the belt transects in the study area.Here,we evaluated whether these characteristics(e.g.,aboundance,morphology,nectar,life form and diet,etc.)affect the structure of ecological network.The main results are as follows:(1)A total of 71 species of birds were recorded in the alpine environment of the study area,belonging to 27 families and 6 orders.We recorded 19 passerine bird species belonging to 10 families interacting with 7 plant species.The frequency of visiting flowers reached 808 times.Rhododendron mekongense was not visited by birds among the 8 studying flowering species.The most visited plants were R.neriiflorum,followed by R.arizelum,R.praestans and R.sidereum.The most flower-visiting birds were Yuhina gularis,followed by Aethopyga ignicauda,Phylloscopus pulcher,Trochalopteron affine and Myzornis pyrrhoura.(2)According to the characteristic parameters of network,it indicates that Rhododendron-bird pollination network in the alpine environment has a non-random structure,including uneven degree distribution,asymmetric interactions,nestedness,low connectance and modularity.Among them,the structure of prominent nestedness can effectively reduce competition between species and promoting coexistence.(3)The most generalized R.neriiflorum was a key species to maintain network nestedness,and high richness with other Rhododendron species play an important role in maintaining the network nested structure.Some bird species(i.e.Yuhina gularis)were a hub species of the network which have a wide range in dietcomposition,low specialization and high abundance,they were extremely important for maintaining network modularity.Therefore,species with high abundance and generalization in the network should be the primary protection object from the perspective of protection.(4)The canonical variable analysis(CVA)and correlation analysis of the morphological data with important species in the network,and showed that the morphology of each species was significantly different.And significant correlation exist between the bill length of male Aethopyga ignicauda and the corolla length of R.neriiflorum.Species that were morphologically similar and closely related plants Rhododendron tend to interact with the same avian pollinators.(5)The nectar volume of Rhododendron have the highest explanatory power for the network structure,it largely supports the "Species preference hypothesis".Based on the relative abundance of bird species,partially supporting the "Neutral hypothesis" of network formation,and pattern matching using morphological probing supports the "Trait-matching hypothesis" to a certain extent.Therefore,three hypotheses together positively affects network structure.Overall,our results show the importance of nectar reward as drivers of plant-pollinator network structure in alpine environment.