Data from: Extinction debt of a common shrub in a fragmented landscape

1. Environmental stochasticity and low demographic rates may cause delayed extinctions of habitat-specialist species that were initially retained within remnant patches after habitat loss and fragmentation. Detecting such extinction debts opens opportunities to counteract future biodiversity loss, yet knowing the underlying causes of population declines is a basic need for targeting specific guidelines for conservation and restoration (e.g. habitat quantity, quality, or connectivity).
2. Here, we examine the extinction debt in the common Mediterranean shrub Myrtus communis (myrtle) occurring in woodland patches of a highly fragmented region that has lost nearly half of the remnant woodland cover during the last fifty years (1956–2002).
3. We sampled myrtle occurrence in 304 woodland patches and modelled its probability of occurrence in relation to patch size, patch disturbance and woodland cover in the surrounding landscape. In order to test for extinction debt evidence, we tested whether myrtle occurrence is better predicted by past (1956) than by present (2002) woodland cover.
4. We found that the probability of myrtle occurrence is associated with present patch features (size and disturbance) that are linked to causes of individual mortality and/or recruitment collapse. However, it was associated with past – rather than present – woodland cover in the surrounding landscape, proving a still unpaid extinction debt. Specifically, myrtle occurrence is very unlikely in small and highly disturbed patches located in long-term deforested landscapes.
5. Synthesis and applications. Individual longevity of the Mediterranean shrub Myrtus communis (myrtle) can delay local extinctions, but paying the debt is a matter of time, especially considering the elevated susceptibility of small and disturbed populations to environmental stochasticity. However, these populations still offer management opportunities and reducing disturbances and improving habitat quality, especially within small woodland patches, should be a top priority for conservation and restoration.

1. 环境随机性与低种群统计率可能导致生境专性物种（habitat-specialist species）的延迟灭绝——这类物种最初在生境丧失与片段化后仍残存于剩余生境斑块中。探明此类灭绝债务（extinction debt）可为遏制未来生物多样性丧失提供契机，而明确种群衰退的根本成因，则是制定针对性保护与修复指南（如生境数量、质量或连通性）的基础前提。
2. 本研究针对高度片段化区域林地斑块中的常见地中海灌木香桃木（Myrtus communis，myrtle）展开灭绝债务相关分析——该区域在1956–2002年的五十年间，已丧失近半数剩余林地覆被。
3. 我们对304个林地斑块中的香桃木出现情况开展了调查，并构建了其出现概率与斑块面积、斑块干扰程度及周边景观林地覆被的关联模型。为验证灭绝债务的存在证据，我们对比了基于1956年（历史）与2002年（当前）林地覆被对香桃木出现情况的预测效能，以判断前者的预测能力是否更优。
4. 研究结果显示，香桃木的出现概率与当前斑块特征（面积与干扰程度）相关，而这些特征与个体死亡和/或种群补充崩溃的成因存在关联；但其出现概率却与周边景观的历史林地覆被（而非当前林地覆被）显著相关，这证实了尚未偿付的灭绝债务的存在。具体而言，位于长期毁林景观中的小型且受干扰程度高的斑块内，香桃木出现的概率极低。
5. 总结与应用：地中海灌木香桃木（Myrtus communis）的个体寿命可延缓局地灭绝进程，但灭绝债务的偿付只是时间问题——尤其是考虑到小型且受干扰的种群对环境随机性的敏感性显著升高。尽管如此，此类种群仍具备管理契机：降低干扰程度、提升生境质量（尤其是在小型林地斑块内），应成为保护与修复工作的首要任务。