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，特别是在水位较低的夏季。较暖的温度会导致许多水生昆虫比较冷的温度生长得更快，出现得更早。考虑到特定河流内发生的温度变化，昆虫出现的时间并不同步。昆虫首先从温暖的栖息地出来，然后再从凉爽的栖息地出来。可变的水生昆虫出现延长了水生昆虫从河流中出现的总时间，并比所有昆虫同时出现时向捕食者提供食物的时间更长。这个项目调查了自然栖息地的温度变化如何维持从河流中长时间出现昆虫，以及这种变化对捕食者(如鱼)生长的影响，这些捕食者以河流中出现的昆虫为食。关于自然界环境变化对生物多样性和物种相互作用的影响，人们已经讨论了它的重要性，但对空间和时间变化的相互作用的研究较少。该项目研究了空间变化如何通过关键猎物物种的空间异步化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，包括加利福尼亚州的一种猎用鱼类钢头鲑鱼。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重要性，但在支持健康鱼类种群的轻型河流恢复工作中，需要野外生态学家给予更多关注。斑点麻蝇从阳光充足的主干河流中出现，飞入黑暗、无生产力的支流，产卵，然后死亡。它们的大规模迁徙补贴了朝贡捕食者，否则这些捕食者将受到食物限制。在这个项目中，关于主茎的空间非生物异质性会加强斑点金枪鱼补贴对支流幼鱼生长的影响的假设，将通过三种方式进行验证。1]大田饲养实验，以了解主干河地貌和水文异质性造成的温度异质性是否在空间上改变了斑点金枪鱼的出现时间；[2]同位素分析将解决这样的问题，即成鱼的不同步出现和向支流的迁移是否延长了营养补贴，否则只是一个短暂的脉冲；[3]大田操纵实验，以确定在其关键的夏季生长期，斑点金枪鱼延长的资源补贴是否增加了营养转移的效率，从而提高了幼鱼的总生长。

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.