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（environmental stochasticity）与低种群统计率可能导致生境特化种（habitat-specialist species）的延迟灭绝——这类物种最初在生境丧失与片段化（habitat loss and fragmentation）后仍留存于残存斑块中。探测此类灭绝债务（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原因，则是制定针对性保护与修复指南（例如栖息地数量、质量或连通性）的基本前提。 2. 本研究聚焦于高度破碎化区域林地斑块中的常见地中海灌木香桃木（Myrtus communis），该区域在1956–2002年的近五十年间已丧失近半残存林地覆盖度。 3. 我们对304个林地斑块中的香桃木分布情况进行了采样，并针对其出现概率构建模型，分析其与斑块面积、斑块干扰度及周边景观林地覆盖度的关联。为检验灭绝债务的证据，我们比较了基于过去（1956年）与当前（2002年）林地覆盖度对香桃木分布的预测效果。 4. 研究发现，香桃木的出现概率与当前斑块特征（面积与干扰度）相关，而这些特征与个体死亡或更新崩溃的诱因存在关联；但其分布却与周边景观的过去而非当前林地覆盖度相关，这证实了尚未偿付的灭绝债务。具体而言，位于长期森林砍伐景观中的小型且受高度干扰的斑块内，香桃木几乎不会出现。 5. 综合与应用：地中海灌木香桃木的个体寿命可延缓局地灭绝，但偿付这笔债务只是时间问题，尤其是考虑到小型受干扰种群对环境随机性的易感性显著升高。不过此类种群仍具备管理潜力，减少干扰并提升栖息地质量（尤其是在小型林地斑块内）应成为保护与修复工作的重中之重。