Island-sharing by archipelago species
Island-sharing by archipelago species
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群岛物种共享岛屿
作者：
Alan Roberts;L. Stone
SummaryDiamond（1975）为群岛中岛屿上的鸟类物种制定了“集合规则”，这使得成功的殖民基本上取决于其他物种的存在。康纳和辛贝洛夫（Simberloff，1979）对这些规则进行了批判性的研究，认为在瓦努阿图（新赫布里底群岛），关于物种分布的实地数据与零假设非常一致，即物种随机定居，没有物种相互作用。他们的工作反过来受到批评（Diamond and Gilpin（1982），Gilpin and Diamond（1982））和激烈的争议随之而来。在这里，我们贡献了一种方法，其中一个简单但迄今被忽视的统计数据被用作探针：一对物种共享岛屿的数量，以及它的一阶和二阶矩。这些共享值的矩阵作为关联矩阵的简单乘积给出，并且它的性质被检查--首先，对于场数据，然后在康纳和辛伯洛夫（1979）使用的随机系综中。它表明，他们的限制保持恒定的平均数共享，所以任何下降的数量，一对物种共享，由于他们排除对方，必须意味着一个上升的数量共享的一些其他物种对，即，转向共享的数字的二阶矩，示出了其在瓦努阿图现场数据中的值超过在1000个矩阵的样本中找到的最大值，这些矩阵被构造成使得它们服从康纳和Simberloff约束，但在其他方面是随机的。这表明，在物种的实际分布中存在排斥和/或聚集效应，而这些效应并没有被零假设所考虑，因此，当检验同一个系综时，所观察到的分布比康纳和辛伯洛夫（1979），甚至比戴蒙德和吉尔平（1982）所发现的要异常得多。寻求这种分歧的原因，并提供一些警告，支持数值证据，关于使用卡方检验时，所涉及的数据点是相互依赖的。
SummaryDiamond (1975) formulated “assembly rules” for avian species on islands in an archipelago, which made a successful colonisation depend essentially on which other species were present. Critically examining these rules, Connor and Simberloff (1979) maintained that, in the Vanuatu (New Hebrides) archipelago, the field data on species distribution was quite compatible with a null hypothesis, in which species colonise at random with no species interaction. Their work was in turn criticised (Diamond and Gilpin (1982), Gilpin and Diamond (1982)) and a vigorous controversy has ensued.Here we contribute a method in which a simple but hitherto neglected statistic is used as a probe: the number of islands shared by a pair of species, with its first and second moments. The matrix of these sharing values is given as a simple product of the incidence matrix, and its properties are examined — first, for the field data, and then in the random ensemble used by Connor and Simberloff (1979). It is shown that their constraints hold constant the mean number shared, so that any fall in the number that one pair of species share, due to their excluding each other, must imply a rise in the number shared by some other species pair-i.e., an aggregation.Turning to the second moment of the numbers shared, it is shown that its value in the Vanuatu field data exceeds the largest value to be found in a sample of 1000 matrices, these latter being constructed so that they obey the Connor and Simberloff constraints but are otherwise random. This indicates that exclusion and/or aggregation effects are present in the actual distribution of species, which are not catered for by the null hypothesis.The observed distribution thus emerges as much more exceptional than found by Connor and Simberloff (1979), and even by Diamond and Gilpin (1982), when examining the same ensemble. The reason for this disagreement are sought, and some cautions are offered, supported by numerical evidence, concerning the use of the chi-square test when the data points involved are mutually dependent.