Climate change and species range margins: predicting forest resilience in the Mediterranean region

物种地理分布的变化是全球气候变化的主要生态影响之一。目前的变暖与在大量物种中观察到的向极地和上坡范围的扩大有关。这些“前沿”范围扩展支持了范围边缘代表物种环境耐受极限的假设，这一假设是广泛用于预测气候变化对生物多样性影响的相对简单的气候包络模型的基础。然而，这一假设同样预测，范围收缩应该发生在赤道的“后缘”边缘，因为种群被推到超出其容忍的极限，但这种收缩发生的证据要少得多。后缘种群的动态尚未得到很好的理解，这暴露了我们对气候变化生物地理学的理解存在重大差距。山毛榉占主导的森林在物种范围边缘在Vall d'Aran，加泰罗尼亚，西班牙东北部。对于这种理论与证据之间的差异，人们提出了几种解释。气候驱动的后缘种群灭绝可能有很长的滞后时间，掩盖了气候变化造成的灭绝债务。或者，后缘种群可能在当地适应了它们的环境，因此与范围核心的种群一样能够忍受变暖。或者，生物相互作用可能比直接的气候限制更能决定赤道范围的边缘。显然，更好地了解后缘种群的动态对于改善气候变化对生物多样性影响的预测至关重要。该项目将大大提高我们对气候如何影响后缘种群中个体表现的理解，以及这如何转化为气候变化下的种群趋势。为此，我们将在西班牙东北部加泰罗尼亚的欧洲山毛榉（Fagus sylvatica）的范围边缘进行一项正在进行的研究。选择了40个研究种群，跨越地理边缘（孤立或与其他种群相连）和生态边缘（在良性或极端气候和生态条件下生长）的梯度。结合现有的长期数据和通过地中海山区森林实地工作收集的新数据，您将执行高级统计分析并构建适合单个种群的种群模型。这将使我们能够预测未来的人口趋势，并测试地理和生态边际性是否会增加或减少对气候变化的适应能力。加泰罗尼亚蒙特塞尼山脉的温带山毛榉林和地中海霍尔姆橡树林之间的边界。

Shifts in the geographical distributions of species are one of the major ecological impacts of global climate change. Current warming is associated with the poleward and uphill range expansions that have been observed across large numbers of species. These 'leading edge' range expansions support the hypothesis that range margins represent the limits of species' environmental tolerances, and this hypothesis underlies the relatively simple climate envelope models widely used to predict biodiversity impacts of climate change. However, this hypothesis equally predicts that range retraction should occur at the equatorial 'trailing edge' margin, as populations are pushed beyond the limits of their tolerance and yet there is much less evidence for such retractions occurring. The dynamics of trailing edge populations are not well understood, exposing a major gap in our understanding of climate change biogeography. Beech-dominated forest at the species range edge in Vall d'Aran, Catalonia, NE Spain.Several explanations for this disparity between theory and evidence have been proposed. There may be long time lags for climate driven extinction of trailing edge populations, masking an extinction debt from climate change. Alternatively, trailing edge populations may be locally adapted to their environment and therefore equally able to tolerate warming as populations in the range core. Alternatively, biotic interactions may be a stronger determinant of equatorial range margins than direct climatic limitation. Clearly, developing a better understanding of the dynamics of trailing edge populations will be crucial for improving predictions of the biodiversity impacts of climate change.This project will substantially advance our understanding of how climate influences the performance of individuals in trailing edge populations and how this translates into population trends under climate change. To do this, we will build on an ongoing study at the range edge of European beech (Fagus sylvatica) in Catalonia, NE Spain. Forty study populations have been selected to span gradients of geographic marginality (isolated or connected to other populations) and ecological marginality (growing in benign or extreme climatic and ecological conditions). Using a combination of existing long-term data and new data collected through field work in Mediterranean mountain forests, you will perform advanced statistical analysis and construct population models tailored for individual populations. This will allow us to project future population trends and test whether geographical and ecological marginality increase or decrease resilience to climate change. The boundary between temperate beech forest and Mediterranean holm oak forest in the Montseny Mountains, Catalonia.