Do Riparian Habitat Disturbances that Alter Cross-habitat Resource Subsidies Magnify Effects of Nonnative Fish Invasions on Stream Food Webs?

改变跨栖息地资源补贴的河岸栖息地干扰是否会放大非本地鱼类入侵对溪流食物网的影响？

• 批准号: 0108222
• 负责人: Kurt Fausch
• 金额: $ 30.12万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-09-01 至 2005-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0108222&HistoricalAwards=false
• 关键词: Do; Riparian; Habitat; Disturbances; Alter

DEB-0108222FauschHabitat destruction and biotic invasions are the two leading agents of global environmental change causing loss of species worldwide. An estimated 40-50% of the land on Earth has been degraded by human actions, and more than 90% of riparian zones adjacent to streams have been altered. Nonnative species invasions cost $137 billion annually worldwide to control. Habitat degradation and species invasions occur simultaneously in most ecosystems and are believed to interact strongly, but there is little experimental evidence to help predict what kinds of habitat disturbances will facilitate invasions or increase their effects. The field experiments proposed here test the idea that riparian habitat disturbances that reduce inputs of terrestrial invertebrate prey from forests to headwater streams during summer magnify the direct and indirect effects of invading fish on stream food webs. In addition, effects of the fish invaders on stream invertebrates are predicted to reduce reciprocal subsidies of emerging aquatic insects from stream to forest during fall through spring. If so, this will demonstrate the potential for habitat loss and fish invasions to have negative indirect effects on terrestrial consumers like birds and spiders. Experiments by Japanese ecologists showed that excluding terrestrial insects from a stream in northern Japan using a canopy (to mimic the usual result of riparian habitat disturbance) caused native trout (charr) to deplete herbivorous stream invertebrates, producing a 'top-down' trophic cascade that increased algal biomass. Further research showed that inputs of forest terrestrial insects (TI) to the stream during summer supplied about 50% of the annual energy budget of fishes, and that aquatic insects emerging from the stream supplied about 25% of the annual energy budget of forest birds. Rainbow trout, a globally-important nonnative stream fish, are rapidly invading streams in northern Japan, apparently exclude native charr, and specialize on TI. Therefore, the current experiments will compare controls with native charr alone in replicate stream reaches to two treatments, one where rainbow trout are added, and another with rainbow trout added but TI excluded using stream canopies. Direct effects of rainbow trout are predicted to reduce native charr growth, abundance, and ultimately to exclude native species via emigration and mortality. Exclusion of TI as well is predicted to intensify effects of rainbow trout on native charr, reduce benthic invertebrate biomass and species richness, and reduce aquatic insect emergence that supplies forest consumers. Predicted indirect effects include foraging shifts by charr that further reduce benthic invertebrate biomass, increase algal biomass via a trophic cascade, and reduce cross-habitat flux of emerging aquatic insects that subsidize forest consumers. This will be the first large-scale experiment to test the idea that human disturbance in one habitat can exacerbate effects of an invasion in another. A richer understanding of the interactions between habitat disturbances and biotic invasions in complex real-world food webs is needed to foster more complete theory in both fields, and to aid natural resource managers attempting to conserve native fish, invertebrate, and bird diversity.

栖息地破坏和生物入侵是全球环境变化导致世界范围内物种丧失的两个主要因素。据估计，地球上40%-50%的土地已经被人类活动退化，超过90%的河岸带毗邻河流已经改变。全球每年要花费1370亿美元来控制外来物种入侵。栖息地退化和物种入侵在大多数生态系统中同时发生，并被认为是强烈的相互作用，但几乎没有实验证据来帮助预测哪种类型的栖息地干扰将促进入侵或增加其影响。这里提出的野外实验测试的想法是，河岸栖息地扰动减少了夏季从森林到源头溪流的陆生无脊椎动物猎物的输入，放大了入侵鱼类对溪流食物网的直接和间接影响。此外，鱼类入侵者对溪流无脊椎动物的影响预计将减少秋季至春季期间从溪流到森林对新出现的水生昆虫的相互补贴。如果是这样的话，这将证明栖息地丧失和鱼类入侵的可能性对鸟类和蜘蛛等陆地消费者产生负面的间接影响。日本生态学家的实验表明，在日本北部的一条溪流中，使用树冠(模仿河岸栖息地干扰的常见结果)将陆地昆虫排除在外，会导致本土鲑鱼(Charr)耗尽食草性溪流中的无脊椎动物，产生一种自上而下的营养级联，从而增加藻类的生物量。进一步的研究表明，夏季输入到溪流的森林陆生昆虫提供了鱼类全年能量收支的50%左右，而从溪流中涌出的水生昆虫提供了森林鸟类全年能量收支的25%左右。彩虹鲑鱼是一种全球重要的外来溪流鱼类，正迅速入侵日本北部的溪流，显然不包括当地的Charr，并专门研究TI。因此，目前的实验将在复制溪流到达两个处理时将对照与单独的本地炭进行比较，一个处理是添加彩虹鲑鱼，另一个是添加彩虹鲑鱼，但不包括使用溪流树冠的TI。据预测，虹鲑鱼的直接影响将减少当地碳素的生长和丰度，并最终通过移民和死亡将当地物种排除在外。排除TI也被预测将加剧虹鲑鱼对本地炭的影响，减少底栖无脊椎动物的生物量和物种丰富度，并减少供应森林消费者的水生昆虫的出现。预计的间接影响包括碳的觅食转变，这将进一步减少底栖无脊椎动物的生物量，通过营养级联增加藻类生物量，并减少补贴森林消费者的新兴水生昆虫的跨生境通量。这将是第一次大规模实验，测试人类在一个栖息地的干扰会加剧另一个栖息地入侵的影响的想法。需要对复杂的现实世界食物网中栖息地干扰和生物入侵之间的相互作用有更丰富的理解，以促进这两个领域更完整的理论，并帮助自然资源管理者试图保护本地鱼类、无脊椎动物和鸟类的多样性。