DISSERTATION RESEARCH: Impacts of human activities on aquatic insect emergence and effects on terrestrial food webs

落入溪流的树叶为许多水生生物提供了食物。同样，河流也为陆地环境提供了物质。水生昆虫一生中大部分时间是作为幼虫在水中度过的，但成年后会飞进森林，为蜘蛛、蜥蜴、鸟类和蝙蝠等陆地捕食者提供重要的食物。因此，溪流和邻近的森林紧密相连。人类活动可能会影响这些生态系统之间能量和物质的相互流动。我们早就认识到人类活动对物质从景观流向溪流的影响。例如，密集的农业活动已知会改变溪流中水生昆虫的群落组成，减少敏感的水生昆虫，而有利于对污染、营养增加和密集农业造成的低氧条件耐受的昆虫。这些与土地利用有关的水生昆虫群落的变化可以反映在出现的昆虫种类和数量及其向陆地的移动上，从而对陆地捕食者及其猎物产生影响。然而，关于土地利用变化如何影响物质从河流到陆地的运输，人们知之甚少。怎么啦？此外，我们对水生昆虫向陆地移动的大部分知识来自于对温带森林地区的研究，这使得我们对物质从河流到陆地的移动如何影响人类改变系统中的陆地食物网的理解存在空白，特别是在热带地区。拟议的研究整合了广泛的本科培训和指导，通过NSF GK-12计划进行的教师培训，社区外展以及对拉丁美洲研究生的支持。在哥斯达黎加的初步研究表明，水生昆虫的密度和生物量以及河滨地栖蜘蛛的密度随着农业土地利用强度的增加而增加，并且水生昆虫的群落组成在土地利用梯度上发生变化。通过野外实验，本项目旨在了解这些变化背后的机制，以及对陆生昆虫密度和群落组成的影响。计划中的实验将操纵水生昆虫在四条森林溪流和四条农业用地密集的溪流上的运动，并量化蜘蛛及其陆生猎物的反应。该方法将检验土地利用对水生昆虫的影响是否为河岸蜘蛛随农业用地增加而增加的机制，并将检验土地利用对水生昆虫的影响是否通过陆地食物网传播，从而影响蜘蛛的陆生昆虫猎物。

Leaves falling into streams provide food for many aquatic organisms. Likewise, streams contribute materials to the terrestrial environment. Aquatic insects spend most of their life in the water as larvae, but emerge as adults and fly into forests, providing important food for terrestrial predators such as spiders, lizards, birds, and bats. Streams and their adjacent forests are thus intimately connected. Human activities may affect this reciprocal movement of energy and materials between these ecosystems. We have long recognized the effect of human activities on the movement of materials from the landscape to streams. For instance, intense agricultural activities are known to change the community composition of aquatic insects in streams by decreasing sensitive aquatic insects and favoring insects tolerant to pollution, increased nutrients, and the low oxygen conditions resulting from intense agriculture. These land-use-associated changes to aquatic insect communities could be reflected in the kinds and amount of insects emerging and their movement to land, with consequences for terrestrial predators and their prey. Little is known, however, about how land use change could affect the transport of materials from streams to land. What?s more, most of our knowledge on the movement of aquatic insects to land comes from research in temperate, forested areas, leaving a gap in our understanding of how the movement of materials from streams to land affects terrestrial food webs in human-altered systems, particularly in the tropics. The proposed research integrates extensive undergraduate training and mentoring, teacher training through the NSF GK-12 program, community outreach, and support for a Latin American graduate student.Initial research in Costa Rica suggests that aquatic insect density and biomass, and streamside terrestrial spider density increase with the intensity of agricultural land-use, and the community composition of aquatic insects changes across a land use gradient. Using a field experiment, this project aims to understand the mechanisms behind these changes, and the consequences for terrestrial insect density and community composition. The planned experiment will manipulate the movement of aquatic insects to land at four forested streams and four streams with intensive agricultural land use, and quantify the response of spiders and their terrestrial prey. The approach will test whether land use effects on aquatic insects is the mechanism for the observed increase in riparian spiders with increasing agricultural land use, and will test whether land-use effects on aquatic insects propagate through the terrestrial food web to affect terrestrial insect prey of spiders.