Comparison Of Two Bird-mediated Mutualistic Systems (Dispersal And Pollination) In Bird Assemblage And Network Properties At A Tropical Rainforest In Xishuangbanna, Southwest China

The interactions between plants and their animal pollinators and seed dispersers have mounted much of Earth’s biodiversity. Both pollination and seed dispersal are the critical process of plants’ reproduction. To understand how the morphological traits of plants influence visiting birds both as seed dispersers and pollinators will help to understand the degree of diffuse co-evolution involved between birds and their food plants. Here I present a comparative study on two mutualistic systems at a tropical rainforest in Southwest China, where different study sites in the forest experienced a range of anthropological disturbance. The aim of this study is to compare how bird assemblage is influenced by plant morphological characteristics and habitat quality. The central question of this study is:How do plant-animal interaction networks differ in structure nestedness, and how do networks respond to different habitats. The main results are as follows:1. A total of 52 bird species that belong to 16 families were recorded and considered to feed on fruits and nectar from flowers in four study sites. These birds included frugivorous birds (48.1%), omnivorous birds (26.9%), nectarivorous birds (23.1%), and insectivorous birds (1.9%). Bulbuls (Pycnonotidae) (13 spp.,25%) were the most common frugivorous. birds, followed by barbets (Megalaimidae) (6 spp.,11.5%), pigeons (Columbidae) (4 spp., 7.7%), broadbills (Eurylaimidae) (1 sp.,1.9%), and parakeets (Psittacidae) (1 sp.,1.9%). Sunbirds and spiderhunters (Nectariniidae) (7 spp.,13.5%) were the most common nectarivorous birds, followed by flowerpeckers (Dicaeidae) (5 spp.,9.6%). There were some omnivorous and insectivorous birds such as leafbirds (Chloropseidae) (3 spp.,5.8%), white-eyes (2 spp.,3.8%), magpies (Corvidae) (2 spp.,3.8%), orioles (2 spp.,3.8%), starlings (Sturnidae) (2 spp.,3.8%), drongos (Dicruridae) (1 sp.,1.9%), rosefinch (1 sp., 1.9%), bluebirds (1 sp.,1.9%) and laughingthrush (1 sp.,1.9%). Menglun primary forest had highest diversity index (2.54) and bird species (42 spp.), followed by XTBG forest (H’= 2.17,38 spp.), Limestone forest (H’=1.32,32 spp.), and XTBG arboretum (H’=1.32,32 spp.). Frugivorous and nectarivorous birds at XTBG arboretum are similar with XTBG forest (Cs=0.87), more than Limestone forest (Cs=0.69), and Menglun primary forest (Cs= 0.65).2. A total of 35 species of frugivorous and nectarivorous birds were recorded visiting fruiting and flowering plants (67.3% of frugivorous and nectarivorous birds identified in four sites). There were 29 species (belonging to 10 families) of frugivorous birds that were recorded visiting 72 plant species (belonging to 28 families), which were observed feeding on fruits or seeds. Seventeen species belonging to 7 families of nectarivorous birds were recorded visiting 32 plant species (belong to 22 families) and were observed feeding on flower nectar. Eleven species (31.4%) belonging to five bird families fed on both fruits/seeds and nectars.3. The assemblage of frugivorous birds tended to be largely influenced by habitat and characteristics of fruits and fruiting trees, i.e. fruit colour, fruit brightness, fruit type, seed size, number of seeds per fruit, tree height, canopy volume, and crop size. The frugivorous bird-food plant interactions were highly asymmetrically structured, in the four study sites combined and in each individual site. 4. For frugivorous bird-fig plant interactions, the number of bird species visiting different fig trees was significantly influenced by crop size and canopy volume but not fruit colour and fruit size. Habitats appeared to influence the composition of visiting birds. The fig-frugivorous bird interactions were asymmetrically structured, and the degree of nestedness appeared to be influenced by the forest type and degree of disturbance. The same pattern was evident for the frugivorous bird-plant interaction.5. In contrast, the nectarivorous bird assemblage was not significantly influenced by habitat or most of the plant traits (i.e., life form, flower type, tree height, canopy volume, and flower brightness) examined except flower color. Interactions between flower- visiting birds and plants were marginally asymmetrically structured in the four sites combined, while the interactive nestedness did not occur at most of the individual forest sites.The study results suggest that there is more evidence of diffuse coevolution in the asymmetrically structured plant-frugivorous bird interactions than the less- nested interactions of nectarivorous birds and their host plants in this Old World monsoonal tropical rainforest.