| The David's deer(Elaphurus davidians)is a unique and rare protected animal in China.The wild population of Shishou Milu is also the largest in the world.For a long time,the Swan Oxbow has been naturally connected with the Yangtze River which makes the reed and grass flourish in the low beach and the marshland.The middle and high beach also have good growth of forest and grass which provides a natural habitat for the reproduction of the David's deer.The population of Shishou Milu,with a population of1300 and three subspecies has been formed:the reserve,Sanheyuan and Yangbotan.All of them have been released naturally and their wild habits have been restored.However,the development of the population isn't easy.The flood of the Yangtze River in 1996brought serious waterlogging disaster to Swan Island.In 1997,the construction of shatanzi dyke began and it was destroyed by the flood of the Yangtze River in 1998.In1999,shatanzi dyke was finally built,which changed the natural connection between the Swan Oxbow and the Yangtze River.Thus a series of phenological changes in the living environment of the local environment caused the degradation of the living environment of Milu to a certain extent and a series of potential safety hazards have been produced.Therefore,the habitat preference,habitat status,risk and trend of habitat change of Shishou Milu under the existing conditions have become the focus of the industry authorities and researchers.The main research results are summarized as follows:(1)Due to the change of hydrological and climatic conditions and the influence of engineering reconstruction projects in recent years,the habitat characteristics and habitat combination of the Milu in Shishou Milu reserve have changed to some extent.Influenced by the geological and hydrological conditions of the study area,this study taking the hydrological conditions as a distinction,respectively studied the habitat selection of Shishou Milu in the Yangtze River in the wet and dry seasons to provide ideas for the protection and construction of Milu habitat.And it could also provide reference for the selection and extension of the David's deer habitat.The results show that the habitat selection of Milu is different in different seasons,but the main control factors are mainly food,water and external disturbance in the whole year.In order to improve the habitat quality of Milu,it is necessary to control human activities,strengthen the resource protection and water quality screening of Milu habitat and ensure the normal growth of vegetation.From the perspective of habitat construction,a large-scale and continuous quiet habitat should be built.(2)The David's deer is a large wetland animal,its life is very dependent on water source.The decline of water self-purification function will lead to the deterioration of water ecosystem,cause the large-scale reproduction of pathogenic bacteria and lead to Milu death.Therefore,it is necessary to carry out large-scale hydrochemical and hydrobiological trait studies on the water source of the Milu reserve and to seek the change trend of the water body closely related to the health of the Milu at the annual scale and the distribution of risk materials on the spatial scale.It is found that the water quality of the Swan Oxbow is in class II standard all the year round and the water quality is generally poor in spring,especially from April to May.In the whole year,phosphorus level is the main index of water quality deterioration.(3)In this study,the herbaceous plant community in Shishou Milu reserve was taken as the research object and the typical sample plots were selected perpendicular to the old road for the community investigation.Based on x~2test,the interspecific association and correlation of herbaceous dominant species were determined by combining AC(association coefficient)and PC(co-occurrence percentage).The distribution of dominant species in different quadrats and the response of habitats,the herbaceous plants in the typical sample zone of Shishou elk nature reserve can be divided into three functional groups as“shade intolerant hygrophytes”,“shade intolerant meso-hygrophytes”and“shade tolerant meso-hygrophytes”.(4)It is very important for the healthy development of Milu population in Shishou Milu reserve to investigate and study the content of heavy metals in the soil plant system of the core area of Milu reserve and to identify the hidden dangers of heavy metals in the soil plant system of Milu habitat,including the grassland,wetland soil and a variety of Milu feeding plants in the core area of Milu habitat.The results showed that the contents of Cd,Cr and Cu in soil exceeded the standard(NY/T391-2013).In terms of plants,the above heavy metal elements were detected,and the content of Cd and Cr in reed,Beckmannia syzigachne,astragalus and alfalfa exceeded the standard respectively.(5)It has been a long time since the Milu lost its horns in unusual time.A small number of Milu lost their horns in advance every year.In general,the proportion of Milu who lost their horns abnormally is less than 3%.But in recent years,the proportion is close to or even more than 5%.On this problem,previous studies mainly focused on the health of Milu,the change of local domestication and the change of food types but the effect was not significant.Therefore,this study no longer explains it from a pathological point of view,but analyzes the physiological factors of horns formation and exfoliation.The growth and abscission of horn are controlled by sex hormone and nutrition,and this study mainly studies the nutrition and the main factors of affect sex hormone.The analysis shows that there is no significant difference in the overall health,development condition and the general components of horns between the Milu with abnormal shedding horns and the normal.On the premise of limiting the above conditions and combining with the climate and meteorological survey in 2018,it is confirmed that the main reason for abnormal shedding of Milu horns is the lack of light conditions.(6)In order to find out whether the high-frequency and high-intensity activities of Milu in the limited space have the reverse phagocytic effect on the existing habitat beyond its carrying capacity,the grassland,muddy land and dry land in Shishou Milu reserve were Multilevel survey and contrastive analysis at different frequencies.Through the comparison of the physical and chemical properties of the meadow soil in the river beach under different activity frequencies.It is found that the physical and chemical properties of each type of soil are significantly changed due to the activities of Milu;the trampling behavior of Milu makes the soil gradually compacted,the soil bulk density and compactness increase,the water content decrease and the content of available nutrients change in different degrees.In general,the low-frequency activities of Milu still have a strong environmental capacity.(7)With the development of Milu population,the related problems caused by habitat carrying capacity have gradually become the focus of attention.The impact of Milu activities on soil microbial community and abundance is one of the important issues of concern.In this study,we studied several habitat types,and compared the microbial communities and their abundances in different activity frequency,habitat types and soil depths,discussed the influence of Milu activity and habitat types on environmental microorganisms,and analyzed the potential risk of pathogenic microorganisms.The results showed that no matter the grassland or the muddy land,the trampling generally reduced the richness and diversity of soil bacterial community.In terms of bacterial community diversity and abundance,the forest land was the highest and the grassland was the lowest.With the increase of trampling frequency,the relative abundance of Actinobacteria showed a gradual increase in both habitats.At the genus level,Bacillus and Streptomyces are the important pathogenic microorganisms causing Milu diseases.With the increase of the activity and trampling frequency of Milu,the abundance of the above two kinds of pathogens in the grassland habitat increased significantly,which indicated that the current population density of Shishou Milu had an impact on the occurrence of environmental pathogens.(8)Based on the long-term observation and investigation of Milu and its living environment,it quotes part of the comprehensive scientific investigation report of Shishou Milu National Nature Reserve(2016)issued by the Nanjing Institute of Environmental Sciences,MEE,and the targeted suggestions are put forward for the aspects of bottomland drought,food chain change,Water safety and hidden dangers of diseases,including habitat Water diversion,wetland space expansion,food chain protection,hiding place construction and so on. |
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