The impact of large animal extinctions on nutrient fluxes in early river valley civilizations
The impact of large animal extinctions on nutrient fluxes in early river valley civilizations
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DOI：
10.1890/es13-00221.1
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发表时间：
2013-12-01
期刊：
影响因子：
2.7
通讯作者：
Malhi, Yadvinder
中科院分区：
文献类型：
--
作者：
Doughty, Christopher E.;Wolf, Adam;Malhi, Yadvinder
城市化在距今3500 - 5000年前的四个河谷文明中独立开始，这些文明位于肥沃的河谷中，最初有自由放养的大型动物，包括大象，最终在当地灭绝。这些大型动物在营养物质远离洪泛平原附近常见的营养物质浓度梯度的横向传播中具有不成比例的重要作用，而这些动物的局部灭绝将减少营养物质向周围地区的流动。在使用粪便作为肥料之前，这种营养物质的自然传播会提高生产力和粮食产量，如果没有它，洪泛平原以外地区的肥力会立即下降。在这里，我们使用“随机游走”模型计算了这种变化的养分通量，并估计在这些动物消失后，洪泛区以外植被中的磷(P)浓度降低了约40%，这一过程可能需要840至6800年，具体取决于所使用的地区和模型参数。在短期内，我们假设生育率的下降可能减少了粮食产量，并迫使早期的农业生产者从外部地区远离河流，前往更肥沃的洪泛平原。从长远来看，外部地区的产量和人口将会减少，从而限制了这些文明的潜在增长，从而表明失去一种关键的生态系统服务如何对人类产生持续数千年的重要影响。
Urbanization began independently in four river valley civilizations similar to 3,500-5,000 years before the present (ybp) in fertile river valleys that originally had free-ranging large animals, including elephants, that eventually went locally extinct. Such large animals are disproportionally important in the lateral spread of nutrients away from nutrient concentration gradients common near floodplains, and the local extinction of the animals would have reduced this flow of nutrients into surrounding regions. Prior to the use of manure as a fertilizer, this natural spread of nutrients would have increased productivity and food yield, and its absence would have immediately decreased fertility to regions outside the floodplains. Here we calculate this changing nutrient flux using a "random walk" model and estimate that phosphorus (P) concentrations in the vegetation were reduced by > 40% outside the floodplain following the loss of these animals and the process could take between 840 and 6,800 years depending on the region and the model parameters used. In the short term, we hypothesize that the decreased fertility may have reduced food yields and driven early agriculturalists from the outer regions away from rivers towards the more fertile floodplains. In the long term, yield and populations in outer regions would have decreased, constraining the potential growth of these civilizations, thus demonstrating how the loss of a key ecosystem service could have important repercussions for humanity that continue over thousands of years.