The Mechanism Of Ant Community Assembly In Fragmented Habitats Of The Thousand Island Lake

Habitat fragmentation is the process that continuous habitat transforms into many isolated and smaller patches due to the natural forces or human disturbance.Habitat fragmentation will affect biodiversity and the assembly process of species communities,which mainly includes niche-based process(e.g.,environmental filtering and interspecies competition)and neutral process(e.g.,dispersal limitation and ecological drift).Although many studies have revealed the effect of habitat fragmentation on community assembly of a wide range of species,such as plants and birds,they barely focus on ants.Ants play an important role in the ecosystem and are very sensitive to habitat alteration.Therefore,understanding the mechanisms underlying ant community assembly in fragmented habitats will provide insights into impacts of habitat fragmentation on biodiversity loss.Although several researches have focused on the ant community assembly,they treated all species equally so that ignored that species may possess distinct functional traits and have different evolutionary backgrounds(i.e.functional and phylogenetic dimension).Functional dimension may reveal how biological communities respond to different environments and phylogenetic dimension considers the evolutionary relationship between species,which will help us understand the relative importance of different ecological processes in structing biological communities through an evolutionary perspective.Reservoir land-bridge islands system is an ideal platform for investigating the effect of habitat fragmentation on community assembly because it has many advantages,e.g.,same historical background,and clear geographical boundaries.Therefore,we conducted our researches in the Thousand Island Lake,China,a land-bridge island system created by dam construction.Here,we assessed the process of ant community assembly and explored the underlying mechanisms on different fragmented islands with different community assembly models and methods(e.g.,null models)through taxonomic,functional and phylogenetic dimension.We have three main objectives:(1)To explore whether interspecific competition affects the assembly of all ants and different functional groups' communities through taxonomic dimension.(2)To test the nestedness of ant community and different ant functional groups and their influencing factors.(3)To reveal the effects of niche-based process on the community assembly of ant species on islands with different area and isolation by integrating ants' trait distributions and functional and phylogenetic structure.From 2017 to 2018,we used pitfall traps,Winkler extraction and hand collection methods to capture ant species on 33 study islands in the Thousand Island Lake region,China.We also measured five morphological traits(body length,eye width,leg length,mandible length and scape length)and built a species-level phylogenetic tree of all species collected.Based on the above data,we assessed the main ecological processes that affects the assembly of ant communities.The main results are as follows:(1)Ant communities and most ant functional groups(Generalized Myrmicinae,Opportunists,Specialist Predators and Tropical Climate Specialists)supported the constant body-szie ratio model which assumes competition as the main driver of community assembly.Additionally,the number of species combinations found among Specialist Predators was less than expected by chance.(2)The community compositions of ants in the Thousand Island Lake were not nested.For different ant functional groups,species from Subordinate Camponotini and Specialist Predator groups existed nested patterns,and species abundance and island area were the main factors affecting their nestedness.(3)The community-weighted body length and mandible length increased with the increasing of island area.However,the community-weighted eye width,leg length and scape length decreased with the increasing of island area.The combination of different traits on smaller island tended to be those that are able to resist disturbance.The predicted values of functional dispersion(FDis)was positively correlated with the island area.Besides,the values of observed function richness(FRic)and functional dispersion were lower than the predicted values on most smaller islands.Moreover,island isolation had no significant effect on ants' trait distribution.(4)Phylogenetic structure tended to be clustered whereas functional structure tended to be overdispersed.However,both phylogenetic and functional structure increased with the increasing of island area,although neither varied systematically as a function of isolation.Our results show that niche-based process mainly affects the Specialist Predator,which may due to their narrow diets and special habitat requirements.Island area,not isolation,is the main driver of ant biodiversity and community structure on our study islands.On smaller islands,abiotic conditions are often more extreme and homogeneous than on larger islands,resulting in the loss of species that are not welladapted to those conditions.Functional traits better represent the extent to which competition is occurring.On the other hand,phylogenetic data may capture complex relationships that better reflect environmental filtering.Thus,phylogenetic diversity cannot be used as a simple proxy for functional diversity in community research.Our study appeals that further studies of community assembly should incorporate multiple dimensions of biodiversity(i.e.,taxonomic,functional and phylogenetic diversity).