A case study on Landscape Component Niche based on Landscape Pattern Indices: Yanchi,Ningxia Province, China

Yanchi County is located in the agro-pastoral ecotone and belongs to the ecologically fragile area of Northwest China.It is important to study the evolution of landscape pattern to curb its environmental degradation.In order to intuitively show how the landscape pattern of the study area changes over time,Landsat Thematic Mappers(TM)and Landsat Operational Land Imager(OLI)data of 1991,2000,2010 and 2017 were used.This paper attempts to apply niche theories and methods into landscape ecology,and constructs a niche model of landscape components by using"n-dimentional hypervolume niche theory"and landscape pattern indices.By evaluating the spatial and temporal evolution of niche from the perspective of two-dimensional space to reflect the changes of landscape pattern in the study area over the past 26 years,new theories and methods were introduced for the characterization of landscape pattern.The results indicate that:1)The larger the attribute and dominance value of landscape components,the higher the ecological niche and the stronger the control effect on the overall landscape.2)The ecological niche of each landscape component was significantly different,just as its control effect on the overall landscape.3)The dynamic change of the ecological niche of each landscape component was different,with grassland,unused land and arable land always in a high dominant position,although the ecological niche of construction land and water area was always low.In general,the introduction of niche theory into the landscape ecology provided a new method to study the changes in regional landscape pattern.

Genomic variation,origin tracing,and vaccine development of SARS-CoV-2:A systematic review

COVID-19 has spread globally to over 200 countries with more than 40 million confirmed cases and one million deaths as of November 1,2020.The SARS-CoV-2 virus,leading to COVID-19,shows extremely high rates of infectivity and replication,and can result in pneumonia,acute respiratory distress,or even mortality.SARS-CoV-2 has been found to continue to rapidly evolve,with several genomic variants emerging in different regions throughout the world.In addition,despite intensive study of the spike protein,its origin,and molecular mechanisms in mediating host invasion are still only partially resolved.Finally,the repertoire of drugs for COVID-19 treatment is still limited,with several candidates still under clinical trial and no effective therapeutic yet reported.Although vaccines based on either DNA/mRNA or protein have been deployed,their efficacy against emerging variants requires ongoing study,with multivalent vaccines supplanting the first-generation vaccines due to their low efficacy against new strains.Here,we provide a systematic review of studies on the epidemiology,immunological pathogenesis,molecular mechanisms,and structural biology,as well as approaches for drug or vaccine development for SARSCoV-2.