Background: The principle that a single large habitat patch should hold more species than several small patches totalling the same area (SL > SS) is used by conservation agencies to favour protection of large, contiguous areas. Previous reviews of empirical studies have found the opposite, SS > SL, creating the single large or several small (SLOSS) debate. Aims: Review the empirical and theoretical SLOSS literature; identify potential mechanisms underlying the SS > SL pattern; evaluate these where possible. Location: Global. Time period: 1976–2018. Major taxa: Plants, invertebrates, vertebrates. Methods: Literature review. Results: Like previous reviews, I found that SS > SL dominates empirical findings. This pattern remained, although it was somewhat weakened, in studies where sampling intensity was proportional to patch size. I found six classes of theory, and conducted five preliminary evaluations of theory. None of the predictions was supported. The SS > SL pattern held for specialist species groups, suggesting it does not result from incursion by generalists into small patches. I found no evidence for the prediction that the reverse pattern (SL > SS) becomes more common over time since patch creation, through gradual species losses from SS. I found no difference between results for natural and anthropogenic patches. There was also no evidence for predictions that SL > SS is more common when the matrix is more hostile, or for stable than ephemeral patches. Main conclusions: Most empirical comparisons find SS > SL. While there are several potential causes, more empirical work is needed to identify those at play. Meanwhile, conservation practitioners should understand that there is no ecological evidence supporting a general principle to preserve large, contiguous habitat areas rather than multiple small areas of the same total size.

中文翻译：

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为什么几个小块比几个大块包含更多的物种？

背景：保护机构使用单个大栖息地斑块应比总面积相同（SL > SS）的几个小斑块容纳更多物种的原则有利于保护大面积连续区域。先前对实证研究的评论发现相反，SS > SL，造成了单一大或几个小 (SLOSS) 的争论。目的：回顾经验和理论 SLOSS 文献；确定 SS > SL 模式的潜在机制；在可能的情况下评估这些。地点：全球。时间段：1976-2018。主要分类群：植物、无脊椎动物、脊椎动物。方法：文献综述。结果：与之前的评论一样，我发现 SS > SL 主导了实证结果。在采样强度与斑块大小成正比的研究中，这种模式仍然存在，尽管它有所减弱。我找了六门理论课，对理论进行了五次初步评估。没有一个预测得到支持。SS > SL 模式适用于专业物种组，表明它不是由通才侵入小块造成的。我没有发现任何证据表明反向模式（SL > SS）自补丁创建以来随着时间的推移变得更加普遍，通过 SS 的逐渐物种损失。我发现自然斑块和人为斑块的结果没有区别。也没有证据表明 SL > SS 在矩阵更具敌意时更常见，或者比临时补丁更稳定。主要结论：大多数实证比较发现 SS > SL。虽然有几个潜在的原因，但需要更多的实证工作来确定那些起作用的原因。同时，