In a review of landscape-scale empirical studies, Fahrig (2017a) found that ecological responses to habitat fragmentation per se (fragmentation independent of habitat amount) were usually non-significant (>70% of responses) and that 76% of significant relationships were positive, with species abundance, occurrence, richness, and other response variables increasing with habitat fragmentation per se. Fahrig concluded that to date there is no empirical evidence supporting the widespread assumption that a group of small habitat patches generally has lower ecological value than large patches of the same total area. Fletcher et al. (2018) dispute this conclusion, arguing that the literature to date indicates generally negative ecological effects of habitat fragmentation per se. They base their argument largely on extrapolation from patch-scale patterns and mechanisms (effects of patch size and isolation, and edge effects) to landscape-scale effects of habitat fragmentation. We argue that such extrapolation is unreliable because: (1) it ignores other mechanisms, especially those acting at landscape scales (e.g., increased habitat diversity, spreading of risk, landscape complementation) that can counteract effects of the documented patch-scale mechanisms; and (2) extrapolation of a small-scale mechanism to a large-scale pattern is not evidence of that pattern but, rather a prediction that must be tested at the larger scale. Such tests were the subject of Fahrig's review. We find no support for Fletcher et al.'s claim that biases in Fahrig's review would alter its conclusions. We encourage further landscape-scale empirical studies of effects of habitat fragmentation per se, and research aimed at uncovering the mechanisms that underlie positive fragmentation effects.

中文翻译：

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栖息地破碎对生物多样性有害吗？

在对景观尺度实证研究的回顾中，Fahrig (2017a) 发现对栖息地破碎化本身的生态响应（与栖息地数量无关的破碎化）通常不显着（>70% 的响应），并且 76% 的显着关系是正，物种丰度、发生率、丰富度和其他响应变量随着栖息地破碎化本身而增加。Fahrig 得出的结论是，迄今为止，没有经验证据支持这样一种普遍假设，即一群小栖息地斑块通常比相同总面积的大斑块具有更低的生态价值。弗莱彻等人。(2018) 对这一结论提出异议，认为迄今为止的文献表明栖息地破碎化本身通常会产生负面生态影响。他们的论点主要基于从斑块尺度模式和机制（斑块大小和隔离的影响，以及边缘效应）到栖息地破碎化的景观尺度效应的推断。我们认为这种推断是不可靠的，因为：（1）它忽略了其他机制，尤其是那些在景观尺度上起作用的机制（例如，栖息地多样性增加、风险扩散、景观互补），这些机制可以抵消记录的斑块尺度机制的影响；(2) 将小规模机制外推到大规模模式并不是该模式的证据，而是必须在更大范围内进行测试的预测。此类测试是 Fahrig 审查的主题。我们发现不支持 Fletcher 等人关于 Fahrig 评论中的偏见会改变其结论的说法。