Seasonal changes in trophic interactions: physiological mechanisms and consequences for energy and contaminant flow in a Canadian Shield lake

冬季是水生动物一年中的关键时期。气候变化已经在抑制温带地区的冬季条件。考虑到这一点，令人惊讶的是，营养相互作用的季节性变化，特别是在冬季，研究甚少。我的研究的长期目标是预测气候变化将如何影响水生动物和生态系统，通过研究营养相互作用的季节性变化的生理机制和生态系统水平的后果（能量和污染物流动）。在接下来的5年里，我将在夏季、秋季、冬季和春季在一个经过充分研究的湖泊（安大略奥佩翁戈湖）进行季节性采样，以解决3个目标。 在目标1中，MSc 1，2，3和我将使用多个生理指标（能量使用，代谢酶活性，肠道结构和功能）探索鱼类活动水平的季节性变化。与维持冬季活动的鱼类相比，在冬季减少活动水平的鱼类应该耗尽其能量储存，降低代谢酶活性，并减少消化系统的大小和酶活性。 对于目标2，PhD1和我将应用稳定同位素（d13C，d15N，d34S）和具有不同周转率的多个组织（血浆，肌肉）的脂肪酸来确定冬季饮食来源如何有助于鱼类的年度能量和营养供应。我们还将测量营养相互作用的季节性变化如何在多个季节和年份驱动食物网结构（食物链长度和宽度）和重要的生态系统功能（捕食者生物量和身体状况）的变化。 在目标3中，PhD2和我将量化猎物汞（Hg）水平和鱼类饮食的季节性变化以及对鱼类体内汞总负荷的影响。这将为温带湖泊从开放水域到冰层覆盖期的汞吸收和可用性变化提供首批数据。 本研究将培养5名研究生和8名本科生HQP。目标1将提供最全面的了解，到目前为止，不同的鱼类在一个社区已经适应了他们的生理和觅食行为，以科普现有的季节性条件。目标2和3将确定生理和冬季活动的差异如何驱动全年营养相互作用、食物网结构和污染物动态的变化，并产生关于冬季期间缺乏研究的关键能源和汞的新知识。这项工作将通过从根本上确定生态系统对可变条件作出反应的关键机制和过程，在概念上推进生态学领域。它还将导致我们预测哪些物种最容易受到温暖，较短的冬季影响的能力取得突破，促进保护和管理工作，并提供前所未有的能力，以表明加拿大淡水系统在气候变暖下的功能下降。

Winter periods are critical times of the year for aquatic animals. Climate change is already dampening winter conditions in temperate latitudes. Given this, it is surprising that seasonal changes in trophic interactions, especially during winter, are poorly studied. The long term goal of my research is to anticipate how climate change will affect aquatic animals and ecosystems by studying the physiological mechanisms and ecosystem-level consequences (for energy and contaminant flow) of seasonal variation in trophic interactions. Over the next 5 years, I will conduct seasonal sampling in a well-studied lake (Lake Opeongo, Ontario) during summer, autumn, winter and spring to address 3 objectives. In Objective 1, MSc1, 2, 3 and I will explore seasonal changes in fish activity level using multiple physiological indicators (energy use, metabolic enzyme activity, gut structure and function). Fish that reduce their activity level during winter should deplete their energy stores, reduce metabolic enzyme activity and reduce the size and enzyme activity of their digestive system compared to fish that sustain winter activity. For Objective 2, PhD1 and I will apply stable isotopes (d13C, d15N, d34S) and fatty acids of multiple tissues with different turnover rates (plasma, muscle) to identify how winter diet sources contribute to a fish's annual energy and nutrient supply. We will also measure how seasonal changes in trophic interactions drive shifts in food web structure (food chain length and width) and important ecosystem functions (predator biomass and body condition) across multiple seasons and years. In Objective 3, PhD2 and I will quantify how prey mercury (Hg) levels and fish diet change seasonally and affect total fish Hg body burdens. This will provide some of the first data for how Hg uptake and availability change from open water to ice cover periods in a temperate lake. The proposed research will train 5 graduate and 8 undergraduate HQP. Objective 1 will provide the most comprehensive understanding to date of how different fish within a community have adapted their physiology and foraging behavior to cope with existing seasonal conditions. Objective 2 and 3 will identify how differences in physiology and winter activity drive shifts in trophic interactions, food web structures and contaminant dynamics throughout the year and produce new knowledge about critical sources of energy and Hg during poorly-studied winter periods. This work will conceptually advance the field of ecology by fundamentally identifying key mechanisms and processes by which ecosystems respond to variable conditions. It will also lead to breakthroughs in our ability to anticipate which species are most susceptible to warmer, shorter winters, advance conservation and management efforts and provide an unprecedented ability to signal for declines in the function of Canada's freshwater systems under a warming climate.