下列活动中所得到的数值与实际数值相比，可能偏小的是（ ）。
- A.标志重捕法调查池塘中鲤鱼的种群密度时，部分鲤鱼身上的标志物脱落
- B.调查土壤小动物丰富度时，用诱虫器采集小动物时没有打开电灯
- C.样方法调查草地中的蒲公英的种群密度时，样方线上的个体都被统计在内
- D.调查某遗传病的发病率时，以患者家系为调查对象
正确答案及解析
正确答案
解析
标志重捕法的计算公式：种群中个体数(N)／标记总数=重捕总数／重捕中被标志的个体数，若部分鲤鱼身上的标志物脱落，则会导致重捕中被标志的个体数偏小，最终导致实验所得到数值比实际数值大，故A项错误。土壤小动物具有趋湿、趋黑、避高温的特性，所以用诱虫器采集小动物时没有打开电灯会导致采集的小动物数偏少，这样使实验所得到数值与实际数值小，故B项正确。采用样方法调查草地中的蒲公英时，对于边界线上的个体，要计相邻两条边及夹角中的数目，若将样方线上的个体都被统计在内，会导致所得到数值与实际数值偏大，故C项错误。在调查遗传病的发病率时，应在群体中抽样调查，若以患者家系为调查对象会导致所得到数值与实际数值偏大，故D项错误。
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