A co-evolutionary approach to a complex adaptive system

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.