湖沼型血吸虫病疫区钉螺空间自相关的样点尺寸效应

钉螺是血吸虫的唯一中间宿主,与众多地理因子一样,钉螺的空间自相关具有明显的尺度效应。在湖沼型血吸虫病疫区典型洲垸型草洲选择一块50 m×50 m的试验样地,采用推扫式全覆盖方法进行了钉螺普查。用全局空间自相关Moran I指数、局部空间自相关Moran散点图和局部Moran’s I指数,进行了钉螺分布空间自相关的样点尺寸效应研究。结果表明:所有样点尺寸钉螺数目的全局Moran’s I均为极显著空间正相关(P0.001);不同样点尺寸下的钉螺样点在局部自相关Moran散点图上绝大多数集中分布在象限1和象限3内,表明试验样地的钉螺呈空间聚集分布;钉螺样点尺寸越小,用局部Moran’s I指数对单个钉螺样点附近的空间自相关表现得越细微,表明全局Moran’s I指标会掩盖实际存在的局部空间自相关与全局不一致的现象。

SAMPLE UNIT SIZE EFFECTS OF SPATIAL AUTO-RELATION OF Oncomelania hupensis in THE MARSHLAND SCHISTOSOMIASIS EPIDEMIC AREA IN CHINA

Oncomelania hupensis snail is the unique intermediate parasite of schistosomiasoma. The epidemic extent and severity of schistosomiasis depend on its spatial distribution, whose spatial auto-relation, like other geographic factors has obvious scale effects. An experimental field in a typical subtype embankment marshland of the Marshland Schistosomiasis Epidemic Area in China was selected as study subject . A push-broom whole-covered method was adopted to survey the snail count within a 50m^*50m field in the Chayegang marshland near Henghu farm in the Poyang Lake region. Universal spatial auto-relation Moran's I, local spatial auto-relation Moran scatter plot figure and local spatial auto-relation Moran's I were used to study the sample unit size effects of spatial auto-relation of snails. The results showed the universal spatial auto-relation Moran's I was of highly significant positive spatial auto-relation (P<0.001) at all sample unit sizes. The local spatial auto-relation Moran scatter plot figures revealed the snail samples concentrateed on the first and third quadrants, indicating the snail in the experimental field had tendency of spatial aggregation. The results of the local spatial auto-relation Moran's I showed the snail samples in the upper parts and the bottom parts of the experimental field were of significant positive spatial auto-relation (α=0.01), and the spatial auto-relation of the snail samples in the other parts of the experimental field was not significant. The smaller the unit size, the more subtle is the presentation of spatial auto-relation of individual snail sample, and the better is the presentation of instability of spatial auto-relation, denoting the universal spatial auto-relation Moran's I could hide substantial existence of inconsistence of local spatial auto-relation Moran's I with universal spatial auto-relation Moran's I.