DISSERTATION RESEARCH: Thermal heterogeneity in river mainstems prolong a subsidy to tributary salmonids by migratory mayflies

天然河流由许多不同的环境组成。这些环境差异造成了水温的变化，特别是在夏季，当水位较低时。温暖的气温导致许多水生昆虫比寒冷的气温生长得更快，出苗期更早。鉴于某条河流的温度变化，昆虫出现的时间是不同步的。昆虫首先从温暖的栖息地出现，然后是寒冷的栖息地。不同的水生昆虫的出现延长了水生昆虫在河流中的整体出现期，并为捕食者提供了比所有昆虫同时出现更长的时间。该项目调查了自然栖息地的温度变化是如何维持昆虫从河流中长时间出现的，以及这对捕食者（如鱼类）生长的影响，这些捕食者以河流中出现的昆虫为食。关于自然环境变化对生物多样性和物种相互作用的影响，人们已经讨论了其重要性，但对空间和时间变化的相互作用研究较少。该项目研究了空间变化如何通过一个关键猎物物种的空间异步生活史事件转化为时间变化，以及这如何影响能量向捕食者的转移，包括加州的一种猎鱼——钢头鳟鱼。这种空间异质性与其时间和营养后果之间的联系具有普遍的重要性，但在轻度河流恢复工作中需要更多的野外生态学家的关注，以支持健康的鱼类种群。蜉蝣（蜉蝣maculata）从阳光充足的主要河流中出现，飞入黑暗、贫瘠的支流，产卵，然后死亡。它们的大规模迁徙补贴了原本食物有限的支流捕食者。本项目将通过三种方式验证主干线的空间非生物异质性增强了斑马鱼补贴对支流中钢头鳟鱼幼鱼生长的影响。[1]通过野外饲养试验，观察主干河地貌和水文异质性造成的热异质性是否在空间上改变了斑田鼠的出现时间；[2]同位素分析将解决这样一个问题：成虫的出现和向支流的迁移是否延长了营养补贴，否则这只是一个短暂的脉冲；[3]一项野外操作试验，旨在观察斑马鱼长期的资源补贴是否能提高营养转移的效率，从而提高幼年虹鳟在夏季关键生长期的总生长。

Natural rivers are comprised of many different environments. These environmental differences create variation in water temperatures, particularly in summer, when the water levels are low. Warmer temperatures cause many aquatic insects to grow faster and emerge earlier than cooler temperatures. Given the temperature variability which occurs within a given river, timing of insect emergence is not synchronized. Insects emerge from warmer habitats first, then cooler habitats. Variable aquatic insect emergence extends the overall emergence period of aquatic insects from the river, and supply food to predators for a longer period of time than if all insects emerged at once. This project investigates how the temperature variation in natural habitats sustains prolonged insect emergence from rivers, and effects of this on the growth of predators, such as fish, that eat emerging insects from the river. The importance of environmental variation in nature has been discussed with regard to its effects on biodiversity and species interactions, however interactions of variation in space and time are less well-studied. This project investigates how spatial variation translates into temporal variation through spatially asynchronizing life history events of a key prey species, and how that affects the transfer of energy to predators, including the steelhead trout, a game fish in California. This linkage of spatial heterogeneity with its temporal and trophic consequences is of general importance, but needs more attention from field ecologists in light river restoration efforts to support healthy fish populations.The mayfly Ephemerella maculata emerges from sunlit mainstem rivers, flies into dark, unproductive tributaries, oviposits, and dies. Their mass migration subsidizes tributary predators that would otherwise be food-limited. In this project, the hypothesis that spatial abiotic heterogeneity in the mainstem strengthens the effect of the E. maculata subsidy on the growth of juvenile steelhead trout in the tributaries, will be tested in three ways. 1] A field rearing experiment to see if thermal heterogeneity created by the geomorphological and hydrological heterogeneity in the mainstem river spatially varies the emergence timing of E. maculata; [2] Isotope analysis will address the question if asynchronous emergence and migration of adult E. maculata into tributaries prolong a trophic subsidy that would otherwise be only a brief pulse; [3] A field manipulative experiment to see if the prolonged resource subsidy by E. maculata increases the efficiency of trophic transfer, and consequently the total growth of juvenile steelhead trout, during their critical summer growth period.