A co-evolutionary approach to a complex adaptive system

人类是否总是对环境造成毁灭性的负面影响？这个问题的答案令人惊讶地不清楚。一方面，有充分的证据表明人类活动导致了多种物种的灭绝。但另一方面，生态学家也发现，包括人类在内的大型脊椎动物消费者和捕食者也能对生态系统产生积极影响。大型脊椎动物可以为其他生物建造不同的栖息地，就像海狸在溪流中筑坝一样，或者通过捕食来保持食草动物数量的平衡，这样它们就不会过度放牧植物群落，就像狼对麋鹿和鹿所做的那样。移除这一重要的——或“基石”——物种可能会导致灾难性的生态系统转变和大量物种的迅速灭绝，如果没有基石提供的积极影响，这些物种将无法共存。但生态学家也指出，干扰的范围和规模很重要：如果海狸淹没大片地区，多样性可能会减少，而不是增加；如果狼抓走了太多的麋鹿，麋鹿的数量就会减少，河流就会被太多的植被堵塞，鱼类也会受到影响。同样，海狸池塘太少或麋鹿捕食太少也会对环境造成不利影响。是否也存在这样一个对人类活动产生最积极影响的中间干扰的最佳点？斯坦福大学的人类学家丽贝卡·l·伯德博士将通过对小规模社会的深入研究来研究人类可以成为关键物种这一观点，在小规模社会中，环境影响往往在范围上更为中间，因此是研究这些问题的绝佳场所。伯德和她的团队将特别关注一种人为干扰，即土著燃烧，这似乎有助于塑造世界许多地方数千年来动植物的分布。如果土著居民作为一个关键物种，本地植物和动物可能与燃烧共同进化。他们特别感兴趣的是，土著居民传统的焚烧方式是否对土著植物和动物都有积极影响，这样做是否有助于通过促进对传统食物的依赖来支持土著人民的福利。在美国，很少有土著社区能够以传统的方式燃烧，因此该团队将前往西澳大利亚干旱草原上的一个偏远社区，那里的燃烧已经持续了数千年。研究人员将调查不同栖息地地区的动植物物种分布，看看它们是如何受到人类狩猎、采集和焚烧活动的影响的；建立一个详细的沙漠食物网；并分析25年来的卫星和航空摄影，绘制出每个地区使用火的历史。这些数据将用于开发和验证计算火灾景观模型，以模拟觅食决策动态，共享和资源分配的社会结构，以及斑块镶嵌燃烧对景观结构和组成以及小型哺乳动物栖息地多样性的影响。虽然该模型将用于澳大利亚草原的案例，但它将推广到其他以火为主的生态系统，如加利福尼亚州。研究人员将把这个模型带给Yurok部落的同事和合作者，他们目前正试图用规定的火恢复当地生态系统和传统食物。除了增加对人类生态作用的科学认识外，这项研究的结果还将为保护和土地管理政策提供信息。如果这项研究支持人类可以作为关键因素的假设，那么人类通过传统管理提供的生态产品和服务可能相当重要，每年可以节省数百万美元的栖息地恢复和规定的火灾。

Do humans always have devastatingly negative environmental impacts? The answer to this question is surprisingly unclear. On the one hand, there is good evidence that human activities have resulted in multiple species extinctions. But, on the other hand, ecologists also have found that large vertebrate consumers and predators, a category that includes humans, can have positive ecosystem effects, as well. Large vertebrates may construct diverse habitats for other organisms, as a beaver does in damming a stream, or keep herbivore populations in balance through predation so that they do not overgraze plant communities, as wolves do for elk and deer. Removing this important -- or "keystone" -- species can cause catastrophic ecosystem transformation and the rapid extinction of a wide range of species that can no longer co-exist without the positive effects provided by the keystone. But ecologists also point out that the scope and scale of disturbance matters: if beavers were to flood huge areas, diversity would likely decrease, rather than increase; if wolves took too many elk, the elk population would crash and streams would be choked with too much vegetation, causing fish to suffer. Likewise, too few beaver ponds or too little predation on elk would be environmentally ineffective. Is there such a sweet spot of intermediate disturbance with the most positive effects for human activities, too? Anthropologist Dr. Rebecca L. Bird of Stanford University will investigate the idea that humans can be a keystone species through intensive study of a small-scale society, where environmental impacts tend to be more intermediate in scope and thus an excellent site for pursuing these questions.Dr. Bird and her team will focus on one human disturbance in particular, indigenous burning, which appears to have helped to shape the distribution of plants and animals in many parts of the world for millennia. If indigenous populations function as a keystone species, native plants and animals may have coevolved with burning. They are particularly interested in whether traditional burning by an indigenous population has positive impacts on both native plants and animals and, in so doing, helps to support indigenous welfare by facilitating reliance on traditional foods. Few indigenous communities in the United States are able to burn in traditional ways, so the team will travel to a remote community in the arid grasslands of Western Australia where burning has continued for millennia. The researchers will survey plant and animal species distributions over different habitat regions to see how they are affected by human hunting, gathering, and burning activities; develop a detailed desert food web; and analyze 25 years of satellite and aerial photography to map out the history of fire use in each region. These data will be used to develop and validate a computational fire landscape model to simulate foraging decision-making dynamics, social structures of sharing and resource distribution, and the effects of patch mosaic burning on landscape structure and composition, and small mammal habitat diversity. While the model will be developed for the Australian grassland case, it will be generalizable to other fire-dominated ecosystems, such as California. The researchers will bring the model to colleagues and collaborators in the Yurok tribe, who are currently attempting to restore native ecosystems and traditional foods with prescribed fire. Besides increasing scientific understanding of the ecological role of humans, findings from this research will inform conservation and land management policies. If the research supports the hypothesis that humans can act as keystones, the ecological goods and services they supply through traditional management may be quite significant, saving millions of dollars annually in habitat restoration and prescribed fire.