A comparison of alternative methods for estimating population density of the fiddler crab Uca annulipes at Saco Mangrove, Inhaca Island (Mozambique)
A comparison of alternative methods for estimating population density of the fiddler crab Uca annulipes at Saco Mangrove, Inhaca Island (Mozambique)
复制标题
估算莫桑比克伊纳卡岛萨科红树林招潮蟹 Uca annulipes 种群密度的替代方法比较
作者：
A. Macia;Ivaldo Quincardete;J. Paula
在许多研究中，利用双目和洞穴计数法对表面活动蟹进行肉眼计数来估计种群密度。然而，它们的可靠性尚未得到比较的评估。本文比较了三种估算莫桑比克Inhaca岛红树林招潮蟹（Uca annulipes）丰度的方法，这些方法来自三个不同的分区：两个分区只在春潮期间被淹没，一个分区在春潮和小潮期间都被淹没。通过在四个月相的每个子区域绘制10个0.25 m2的样方，进行了洞穴、双目和直接（挖掘）计数方法。总密度（每0.25平方米）因方法、分区和月相而异。地穴计数高估了螃蟹密度达20%，而双眼计数低估了密度达41%。两种计数方法的相关系数估计表明，穴居计数比双目计数能更好地估计密度（分别为0.91和0.56）。还调查了三个分区内和月相的性别比例。除了新月和第一季度外，雄性在整个研究期间都占主导地位，这表明当怀孕的雌性数量较少时，双眼计数的性别比例偏差最小。
Visual counts of surface-active crabs both by binocular and burrow counting methods have been used in many studies to estimate population density. However, their reliability has not yet been assessed comparatively. Three methods for estimating the abundance of fiddler crabs Uca annulipes in a mangrove forest (Inhaca Island, Mozambique) were compared from three different sub-areas: two sub-areas inundated only during spring tides and one sub-area inundated in both spring and neap tides. Burrow, binocular and direct (excavation) counting methods were performed by plotting ten 0.25 m2 quadrats in each sub-area over the four moon phases. Overall densities (per 0.25 m2) differed according to method, sub-area and lunar phase. Burrow count overestimated crab density by up to 20%, while binocular count underestimated density by up to 41%. Correlation coefficient estimated for both counting methods showed that burrow count gives better density estimates than binocular count (0.91 and 0.56, respectively). Sex ratios were also investigated within the three sub-areas and at the moon phases. Males are dominant throughout the studied period except during new moon and first quarter, indicating that when the number of gravid females is low, sex ratio bias for binocular count is minimal.