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，可能会从一个州突然变化到另一个州。这些突变的开始被称为临界点或临界点。人们对找到方法来衡量和预测这些临界点非常感兴趣，以便预测何时会发生临界点，或者系统是否处于临界点的过程中。理解临界点的性质以及如何识别它们的一种方法是研究过去发生的那些临界点。在最近为古生态学家汇编的50个优先问题中，有两个问题涉及研究过去的临界点的必要性。这项提议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的临界点的衡量标准。第二个目的是了解气候和火在加拿大西北部的黑云杉和魁北克的白松北部分布界限的撤退中的联合作用。气候的巨大变化可以驱动过去植物群落组成的重大变化，导致物种范围限制的变化，以及植被带的转移，如北部乔木线的撤退。但是，即使在气候引起的丰度或分布的变化在化石记录中明显之前，一定已经对该物种施加了一些压力。如果过去的压力--古压力--能够被测量，那么我们就可以确定气候变化最初开始影响人口和社区的时间。换句话说，我们将有一个工具来确定气候和社区构成即将发生变化的临界点。我建议用化石花粉对称性的变化作为古压力的指标，以推断过去的临界点。个体的生长和发育取决于其遗传蓝图与环境之间的相互作用。许多生物体及其器官表现出两侧对称，即一半是另一半的镜像。随着个体的成长和发育，偏离对称结构(例如，一只手臂比另一只手臂长)可能会由许多因素引起，包括环境压力。这些偏离对称性的现象被称为“波动不对称”(FA)。FA的变化可以作为临界点的指标。我将研究在过去植被和气候发生重大变化的情况下，两侧对称(看起来像米老鼠豆豆)的针叶树种化石花粉颗粒FA的变化，例如加拿大西北部的林线撤退，以及魁北克白松北部分布界限的南移。这种新的FA用于识别临界点的应用具有潜在的应用于各种环境中的不同生物体，并且信号临界点不仅在气候中，而且在其他环境变量中。

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.