| Crabs,as the ’engineers’ of mangrove ecosystems,play an important role in the functioning of mangrove ecosystems.Uncovering the biogeographic pattern of mangrove crabs and the mechanism of community assembly is critical for the conservation and management of mangrove biodiversity.Currently,the biogeographic pattern and assembly process of the mangrove crab community in China still unknown,which is unfavorable for the protection and management of mangrove biodiversity in one country scale.Large-scale anthropogenic mangroves have been planted on the southeast coast of China,however,the ecological effects of the largescale anthropogenic mangroves on the community and assembly process of mangrove ecosystems are still not well studied,which further hinders the ecological recovery strategy of mangroves in our country.In this study,a camera trap method was used to sample the mangrove crabs across a biogeographic scale in China.We conducted the quantitative and qualitative surveys of the crab community along 11 latitudes(18.24°N to 28.34°N).We totally collected 15 mangrove areas to sample crab community,including Qingmeigang bay,Qinglangang bay,Xinyinggang bay,Dongzhaigang bay,Beilun estuary,Leizhou Peninsula,Hailing Island,Qi’ao Island,Shantou,Zhangjiang estuary,Quanzhou bay,Putian,Luoyuan bay,Shacheng bay,and Ximen Island.To uncover the latitudinal pattern of mangrove crab community diversity in China,we detected two main objectives:(1)revealing the latitudinal pattern of alpha diversity of the mangrove crab community and(2)detecting the pattern of beta diversity and its spatial turnover and nestedness components.Then,to explore the underlying mechanisms of mangrove crab community assembly,we used multiple methods of community assembly to detect three objectives:(1)detecting whether and how interspecific competition affects the assembly of mangrove crabs,(2)exploring whether and how environmental filtering and dispersal limitation affect the mangrove crab communities,and(3)uncovering the relative role of niche-based and neutral processes regulating the mangrove crab communities.Finally,to explore the effects of anthropogenic afforestation on the assembly of mangrove crab communities,we took the mangroves distributed in Fujian province as an example to compare the diversity and assembly process of crab communities between native and anthropogenic mangroves.The main results and conclusions of this study are as follows:(1)We found 249 species of mangrove crabs in China.There are 226 species were identified at the species level and 23 species were identified at the genus level.The Grapsidae and Ocypodidae contained 147 species and were the dominant families,accounting for 59.04%of the total species.We found that Qinglangang bay contained 72 mangrove crab species and was the hot spot for mangrove crabs in China.The latitudinal gradient pattern of the alpha diversity(species richness,Shannon-winner index,and Simpson index)of crab in China was a "humped shape" pattern,that is,the alpha diversity of crab communities firstly increased and then decreased from 18 °N to 28°N,the peak value appeared at 19°N.(2)We found that the average beta diversity of mangrove crabs in China was 0.83,of which the turnover component was 0.70 and the nestedness component was 0.13,indicating that spatial turnover was the main ecological process in the assembly of the mangrove crab community in China.We also found that the overall beta diversity of crabs and their turnover components showed a significant latitudinal gradient pattern,however,the latitudinal gradient pattern of the nestedness components of the crab community was not obvious.(3)The results of the Monte Carlo-based null model showed the observed value of the C-score for mangrove crab communities was greater than the randomly expected value,the standard effect size of the C-score was 3.57,indicating that the mangrove crab communities in China were regulated by interspecific competition and conformed to the Diamond’s assembly rule.(4)We found that the average Euclidean distance of sediments,water environment,and climatic conditions in the mangrove areas of China was 5.27,and the maximum Euclidean distance was 10.1,indicating that the environmental heterogeneity of the mangrove area in China was high.The beta diversity of crab communities and their turnover and nestedness components were significantly influenced by soil total phosphorus content,pH,water temperature,water salinity,daily mean temperature,daily maximum temperature,daily minimum temperature,and spatial vectors MEM1 and MEM2,indicating that both environmental filtering and spatial dispersal limitations significantly affect the mangrove crab communities in China.The results of variation partition analysis(VPA)showed that the overall beta diversity and nestedness components of crab communities were mainly regulated by environmental filtering,while the turnover components were mainly regulated by dispersal limitations.In Fujian province,we found that although the crab diversity in the anthropogenic mangroves(41 species)was less than the crab diversity in the native mangroves(55 species),afforestation increased the availability of habitats and then promoted the colonization of opportunistic species,which ultimately increased the crab diversity of the entire mangroves(65 species).The beta diversity and turnover components of the crab community in the anthropogenic mangrove were larger than those in the natural mangrove,indicating that the spatial turnover rate of the crab community in the anthropogenic mangroves was higher than that in the native mangroves.Compared with the crab community in natural mangrove,the environmental filtering of the crab community in anthropogenic mangrove was increased,but the stochastic processes such as ecological drift and interspecific competition were weakened.This study shows that afforestation promoted the spatial turnover of crab communities by changing multiple ecological processes,including enhanced environmental selection,reduced stochastic process and decreased species competition.These changes ultimately increased the beta diversity of crab communities and resulted in the reorganization of crab communities at a landscape scale.Our results emphasize that afforestation of mangroves significantly affects the diversity of crab communities and results in large-scale reorganization of crab communities.Our findings enrich and develop the theory of community assembly in biogeography,provide theoretical support for the conservation of mangroves biogeography,and even provide a new perspective for the biogeographic rehabilitation and restoration of coastal wetlands. |
