Paleosymmetry: tipping points and the dynamics of range contractions

复杂的系统，如气候，社会和陆地生态系统可能会突然从一个状态到另一个状态。这些突然转变的开始被称为阈值或临界点。人们对找到方法来测量和预测这些临界点有着巨大的兴趣，以便预测何时会发生，或者系统是否处于临界过程中。了解临界点的性质以及如何确定临界点的一种方法是研究过去发生的临界点。在最近为古生态学家编制的50个优先问题中，有两个问题涉及研究过去临界点的必要性。该提案的主要目的之一是首次将花粉粒对称性的变化作为气候和植被变化临界点的衡量标准。第二个目的是了解气候和火灾在加拿大西北部的黑色和白色云杉的北方分布界限和魁北克的白松的撤退中的共同作用。**气候的巨大变化可以驱动过去植物群落组成的重大变化，导致物种分布范围界限的变化，以及植被带的转移，如北方树线的退缩。但是，即使在化石记录中出现气候引起的丰度或分布变化之前，物种也一定受到了一些压力。如果过去的压力-古压力-可以测量，那么我们就可以确定气候变化何时开始影响人口和社区。换句话说，我们将有一个工具来确定气候和社区组成即将发生变化的临界点。我建议使用化石花粉对称性的变化作为古应力的指标，以推断过去的临界点。个体的成长和发展取决于其遗传蓝图与环境之间的相互作用。许多生物体和它们的器官都具有双侧对称性，即一半是另一半的镜像。 随着个体的成长和发育，包括环境压力在内的许多因素可能会导致对称结构的偏离（例如，一只手臂比另一只手臂长）。这些偏离对称性的现象被称为“波动不对称性”（FA）。FA的变化可以作为临界点的指示。我将研究在FA的针叶树种的化石花粉粒是双边对称的（看起来像米老鼠豆豆）在过去的情况下，植被和气候已经发生了显着变化，如树线撤退在加拿大西北部，并向南位移的北方分布限制白松在魁北克。FA用于识别临界点的这种新应用具有应用于各种环境中的各种生物的潜力，并且不仅在气候中而且在其他环境变量中都具有信号临界点。

Complex systems such as climate, societies, and terrestrial ecosystems may change abruptly from one state to another. The start of these abrupt transitions is termed the threshold or tipping point. There is enormous interest in finding ways by which we can measure and anticipate these tipping points in order to predict when one will occur or if the system is in the process of tipping. One approach to understanding the nature of tipping points and how they might be identified is to study those that occurred in the past. In a recent compilation of 50 priority questions for paleoecologists, two questions concerned the need to study past tipping points. One of the primary aims of this proposal is to apply, for the first time, changes in the symmetry of pollen grains as a measure of tipping points in climate and vegetation change. The second aim is to understand the joint roles of climate and fire in the retreat of the northern distributional limit of black and white spruce in NW Canada and white pine in Quebec.******Large changes in climate can drive major changes in past plant community composition, lead to changes in the range limits of species, and shifting of vegetation zones, such as the retreat of northern tree line. But even before climate-induced changes in abundances or distributions are evident in fossil records, there must have been some stress imposed on the species. If that past stress – paleostress – could be measured, then we could determine when climate change first started to impact populations and communities. In other words, we would have a tool to identify the tipping point for impending shifts in climate and community composition. I propose to use changes in the symmetry of fossil pollen as an index of paleostress in order to infer past tipping points.******The growth and development of an individual depends on the interaction between its genetic blueprint and its environment. Many organisms and their organs exhibit bilateral symmetry, i.e. one half is a mirror image of the other half. As individuals grow and develop, deviations from symmetrical structures (one arm longer than another, for example) may be induced by a number of factors, including environmental stress. These deviations from symmetry are termed “fluctuating asymmetry” (FA). Changes in FA may serve as indications of a tipping point. I will study changes in FA of fossil pollen grains of conifer species that are bilaterally symmetrical (look like Mickey Mouse beanies) in past scenarios where vegetation and climate are known to have changed significantly, such as tree line retreat in NW Canada, and southward displacement of the northern distributional limit of white pine in Quebec. This novel application of FA for the identification of tipping points has the potential to be applied to diverse organisms in a wide variety of environments, and signal tipping points not only in climate, but in other environmental variables.