小菜蛾卵空间格局及分层抽样的研究
STUDIES ON THE SPATIAL PSTTERN AND STRATIFIED SAMPLING OF THE EGGS OF DIAMONDBACK MOTH.
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摘要: 小菜蛾卵空间格局有时会出现明显的边际效应。一个反映卵密度（Ｄｅ）与抽样点至宿主分布区边界最短距离（ｈ）关系的新模型：Ｄｅ＝ａ＋ｂｅ－ｃｈ，可以较好地描述这种带边际效应的空间格局。该模型的三个参数都有明确的生物学意义，ａ、ｂ和ｃ分别代表边际效应为零时的卵密度、边际效应最大时的卵密度增量和边际效应衰退系数。由这三个参数可得到边际效应强度指数（ｓ）（ｓ＝ｂ／ａ）和边际效应层宽度（ｗ）（ｗ＝ｌｎ（１０ｓ）／ｃ），前者可用于空间格局形成机制的研究，后者可作为分层抽样的依据。文中还讨论了分层的具体步骤及其分层抽样的理论抽样数。Abstract: In the spatial pattem of the eggs of diamondback moth,Plutella xylostella(L.)there was sometimes obvious edge-effect.Based on the relationship between the eggsdensity(De)and the shortest distance(h)of sample point to the border of thearea of the host plant distribution,a new model was developped:De=a+be-ch,whichcould well describe the spatial pattem with edge-effect.In above model,threeparameters all have explicit biological meanings,a,b,and c denote the density whenedge-effect was not exist,the addition of the density when edge-effect reached themaximum,and the coefficient of the decline of edge-effect respectively. Accordingto these parameters,two indices were gained.One was strength of edge-effect(s)(s=b/a),which could be used to analyse the mechanism for the formation of spatialpattern.Another was width of edge-effect stratum(w)(w=ln(10s)/c,which couldserve as a basis for stratified sampling.The procedure of stratification and theoreticalnumber of samples for stratified sampling were also discussed.
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Keywords:
- Plutella xylostella /
- spatial pattern /
- edge-effect
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