Extinctions | 灭绝 - aleveler.com

📚 Extinctions | 灭绝

Extinction is a fundamental process in the history of life. It removes species from ecosystems and creates opportunities for new forms to evolve, but human activities are now accelerating extinction far beyond natural background rates.

灭绝是生命史中的一个基本过程。它使物种从生态系统中消失，并为新类型的演化创造机会，但人类活动正使灭绝速度远超自然背景水平。

1. Defining Extinction | 灭绝的定义

A species is considered extinct when no living individuals remain anywhere in the world. Extinction can also be described as functional extinction when a population is too small to perform its ecological role or cannot recover.

当一个物种在世界任何地方都不再有存活个体时，即被认为已经灭绝。当种群过小，无法发挥其生态功能或无法恢复时，也可称为功能性灭绝。

The IUCN Red List categories include extinct (EX) and extinct in the wild (EW). In the latter case, individuals survive only in captivity or cultivation, not in their natural habitat.

世界自然保护联盟红色名录的类别包括灭绝（EX）和野外灭绝（EW）。在野外灭绝的情况下，个体仅存活于圈养或栽培环境中，而非自然栖息地。

2. The Fossil Record and Background Extinction | 化石记录与背景灭绝

The fossil record shows that extinction has occurred throughout Earth’s history. Background extinction is the continuous, low-level loss of species caused by normal environmental change, competition, predation and small-scale disturbances.

化石记录表明，灭绝在地球历史上一直存在。背景灭绝是由正常的环境变化、竞争、捕食和小规模干扰引起的持续、低水平的物种丧失。

Background extinction rates are often estimated as 0.1 to 1 species per million species per year. These estimates are uncertain because the fossil record is incomplete and biased towards hard-bodied marine organisms.

背景灭绝率通常估计为每年每百万物种中有0.1至1种灭绝。由于化石记录不完整且偏向于硬体海洋生物，这些估计存在不确定性。

3. Mass Extinction Events | 大规模灭绝事件

Mass extinctions are events in which extinction rates rise far above background levels over a short geological time. The ‘Big Five’ mass extinctions are the end-Ordovician, Late Devonian, end-Permian, end-Triassic and end-Cretaceous events.

大规模灭绝是指在地质短期内灭绝率远高于背景水平的事件。’五次大灭绝’包括奥陶纪末、泥盆纪晚期、二叠纪末、三叠纪末和白垩纪末事件。

The end-Permian extinction, about 252 million years ago, was the most severe, eliminating roughly 96 percent of marine species and 70 percent of terrestrial vertebrate species. The end-Cretaceous extinction, 66 million years ago, removed the non-avian dinosaurs.

约2.52亿年前的二叠纪末灭绝最为严重，大约96%的海洋物种和70%的陆生脊椎动物物种消失。6600万年前的白垩纪末灭绝则消灭了非鸟恐龙。

4. Causes of Extinction: Abiotic Factors | 灭绝的非生物因素

Abiotic causes include asteroid impacts, massive volcanic eruptions, climate change, sea level fluctuations, ocean anoxia and ocean acidification. These factors can alter habitats faster than species can adapt or migrate.

非生物因素包括小行星撞击、大规模火山喷发、气候变化、海平面波动、海洋缺氧和海洋酸化。这些因素改变栖息地的速度可能超过物种适应或迁移的能力。

For example, the end-Cretaceous asteroid impact produced dust and sulphate aerosols that blocked sunlight, disrupted photosynthesis and triggered a global temperature drop. The Siberian Traps volcanic eruptions are linked to greenhouse warming and ocean anoxia during the end-Permian crisis.

例如，白垩纪末的小行星撞击产生的尘埃和硫酸盐气溶胶遮挡阳光，干扰光合作用并引发全球降温。西伯利亚地盾的火山喷发与二叠纪末危机期间的温室变暖和海洋缺氧有关。

5. Causes of Extinction: Biotic Factors | 灭绝的生物因素

Biotic factors include competition, predation, disease, and the introduction of invasive species. A new predator or pathogen can rapidly drive naive prey or host species to extinction, especially on islands.

生物因素包括竞争、捕食、疾病以及外来入侵物种的引入。新的捕食者或病原体可迅速使缺乏防御能力的猎物或宿主物种灭绝，尤其是在岛屿上。

Competition with a more efficient species can reduce a native species’ access to resources. Disease outbreaks, such as chytridiomycosis in amphibians, have caused severe population declines and extinctions.

与更高效物种的竞争会减少本地物种获取资源的机会。疾病暴发，例如两栖动物的壶菌病，已导致严重的种群下降和灭绝。

6. The Role of Genetic Diversity | 遗传多样性的作用

Genetic diversity within a population is essential for adaptation to environmental change. Small populations lose alleles through genetic drift and may suffer inbreeding depression, reducing fertility and survival.

种群内的遗传多样性对于适应环境变化至关重要。小种群会通过遗传漂变丧失等位基因，并可能遭受近交衰退，从而降低繁殖力和存活率。

Effective population size, the number of individuals contributing genes to the next generation, is often much smaller than the census population size. This makes species more vulnerable to extinction than their total numbers suggest.

有效种群大小，即为下一代贡献基因的个体数量，通常远小于实际种群数量。这使得物种比其总数所显示的更容易灭绝。

7. Extinction Vortex and Small Populations | 灭绝漩涡与小种群

The extinction vortex is a positive feedback loop in which small populations become increasingly vulnerable. Demographic, environmental and genetic stochasticity interact, causing numbers to fall further and reducing genetic variation.

灭绝漩涡是一个正反馈循环，小种群在其中变得越来越脆弱。种群统计、环境和遗传的随机性相互作用，使数量进一步下降并减少遗传变异。

For example, inbreeding reduces fecundity, which lowers population size, which in turn increases the effect of genetic drift. Once a population enters this vortex, it may be difficult to reverse without human intervention.

例如，近交降低繁殖力，使种群数量下降，进而增强遗传漂变的影响。一旦种群进入这一漩涡，若不进行人为干预，可能很难逆转。

8. Habitat Loss and Fragmentation | 栖息地丧失与破碎化

Habitat loss is the leading cause of species extinction today. Agriculture, urbanisation, logging and mining destroy or degrade the environments species depend on, reducing carrying capacity and population size.

栖息地丧失是当今物种灭绝的主要原因。农业、城市化、伐木和采矿破坏或退化物种赖以生存的环境，降低环境容纳量和种群大小。

Fragmentation divides continuous habitats into smaller, isolated patches. Edge effects change light, temperature and humidity, while small patches support fewer individuals and are more vulnerable to local extinction.

破碎化将连续栖息地分割成更小、孤立的斑块。边缘效应改变光照、温度和湿度，而小斑块支撑的个体更少，更容易发生局部灭绝。

9. Invasive Species and Overexploitation | 入侵物种与过度开发

Invasive species are non-native organisms that spread rapidly and harm native species through predation, competition, herbivory or disease. Islands are especially vulnerable because their native species often lack defences against introduced predators.

入侵物种是迅速扩散并通过捕食、竞争、取食植物或传播疾病危害本地物种的非本地生物。岛屿尤其脆弱，因为本地物种通常缺乏对引入捕食者的防御。

Overexploitation is the unsustainable harvesting of wild populations. Overfishing, poaching and the bushmeat trade have driven species such as the passenger pigeon and the dodo to extinction, and continue to threaten sharks, rhinos and pangolins.

过度开发是对野生种群不可持续的捕捞或猎取。过度捕捞、偷猎和野味贸易已使旅鸽和渡渡鸟等物种灭绝，并继续威胁鲨鱼、犀牛和穿山甲。

10. Climate Change and Ocean Acidification | 气候变化与海洋酸化

Rapid climate change forces species to shift their ranges, adapt or face extinction. Species with narrow thermal tolerance, limited dispersal ability or specialised habitat requirements are at greatest risk.

快速的气候变化迫使物种改变分布范围、发生适应或面临灭绝。热耐受范围窄、扩散能力有限或栖息地要求专一的物种风险最大。

Ocean acidification, caused by increased atmospheric CO2, reduces carbonate ion availability. This makes it harder for corals, molluscs and plankton to build calcium carbonate shells and skeletons, threatening marine food webs.

大气中二氧化碳增加引起的海洋酸化降低了碳酸根离子的可用性。这使得珊瑚、软体动物和浮游生物更难构建碳酸钙外壳和骨骼，威胁海洋食物网。

11. The Sixth Mass Extinction and Conservation | 第六次大灭绝与保护

Many scientists argue that we are entering a sixth mass extinction. Current extinction rates are estimated to be tens to hundreds of times higher than background rates, driven mainly by human activities.

许多科学家认为我们正在进入第六次大灭绝。据估计，当前的灭绝率比背景灭绝率高数十至数百倍，主要由人类活动驱动。

Conservation strategies include establishing protected areas, restoring habitats, creating wildlife corridors, controlling invasive species, captive breeding and reintroduction, seed banks and international agreements such as CITES. These actions aim to maintain viable populations and genetic diversity.

保护策略包括建立保护区、恢复栖息地、建立野生动物廊道、控制入侵物种、圈养繁殖与重引入、种子库以及《濒危野生动植物种国际贸易公约》等国际协议。这些行动旨在维持可存活的种群和遗传多样性。

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Extinctions | 灭绝