Ecosystem engineers have large impacts on the communities in which they live, and these impacts may feed back to populations of engineers themselves. In this study, we assessed the effect of ecosystem engineering on density-dependent feedbacks for midges in Lake Mývatn, Iceland. The midge larvae reside in the sediment and build silk tubes that provide a substrate for algal growth, thereby elevating benthic primary production. Benthic algae are in turn the primary food source for the midge larvae, setting the stage for the effects of engineering to feed back to the midges themselves. Using a field mesocosm experiment manipulating larval midge densities, we found a generally positive but nonlinear relationship between density and benthic production. Furthermore, adult emergence increased with the primary production per midge larva. By combining these two relationships in a simple model, we found that the positive effect of midges on benthic production weakened negative density dependence at low to intermediate larval densities. However, this benefit disappeared at high densities when midge consumption of primary producers exceeded their positive effects on primary production through ecosystem engineering. Our results illustrate how ecosystem engineering can alter density-dependent feedbacks for engineer populations.

中文翻译：

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生态系统工程改变了水生昆虫种群的密度依赖反馈

生态系统工程师对他们居住的社区有很大的影响，这些影响可能会反馈给工程师群体。在这项研究中，我们评估了生态系统工程对冰岛米湖蠓的密度依赖反馈的影响。蚊幼虫驻留在沉积物中并构建丝管，为藻类生长提供基质，从而提高底栖初级生产。底栖藻类反过来又是蠓幼虫的主要食物来源，为工程效果回馈蠓本身奠定了基础。使用控制蠓幼虫密度的现场中宇宙实验，我们发现密度和底栖生产之间普遍存在正但非线性的关系。此外，成虫羽化随着每只蠓幼虫的初级生产而增加。通过在一个简单模型中结合这两种关系，我们发现蠓对底栖生产的积极影响减弱了低到中等幼虫密度下的负密度依赖性。然而，当初级生产者的蠓消费超过其通过生态系统工程对初级生产的积极影响时，这种好处在高密度下消失了。我们的结果说明了生态系统工程如何改变工程师群体的密度相关反馈。