Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the confounding effects of changing water temperature, we studied the seasonal dynamics of an aquatic invertebrate community and their effect on a top fish predator in a thermally stable freshwater spring in South Iceland. We sampled benthic invertebrates five times over a year and conducted a mark-recapture study on the top predator in the system, small benthic Arctic charr, Salvelinus alpinus (L.). We assessed variation in diet composition and feeding preferences by calculating the electivity and individual specialisation of each fish at each sampling time. There was a clear separation of winter and summer communities for the benthic invertebrates. The variation in prey availability was also reflected in the fish diet, with higher feeding selectivity in summer than in winter for the highly abundant Chironomidae larvae. In contrast, individual specialisation as a measure of intrapopulation niche variation was higher in winter when prey availability was lower. We furthermore found that groundwater amphipods might play an important role in the winter diet of spring-dwelling Arctic charr. In conclusion, seasonal variation in the invertebrate community is an important factor to consider and has the potential to alter the phenotype (e.g. growth rates) and behaviour (e.g. feeding preferences) of higher trophic levels.

中文翻译：

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热稳定春季无脊椎动物群落的季节性变化和顶级鱼类捕食者的饮食

水生无脊椎动物的许多生活史事件是由水温的季节性变化引发的，但其他生态因素也可能很重要。为了排除水温变化的混杂影响，我们研究了水生无脊椎动物群落的季节性动态及其对冰岛南部热稳定淡水泉中顶级鱼类捕食者的影响。我们在一年内对底栖无脊椎动物进行了五次采样，并对系统中的顶级捕食者——小型底栖北极红点鲑 (Salvelinus alpinus (L.)) 进行了标记再捕获研究。我们通过计算每个采样时间每条鱼的选择性和个体专业化来评估饮食组成和喂养偏好的变化。底栖无脊椎动物的冬季和夏季群落明显分开。猎物可用性的变化也反映在鱼类的饮食中，对于高度丰富的摇蚊科幼虫来说，夏季的摄食选择性高于冬季。相比之下，当猎物可用性较低时，个体专业化作为种群内生态位变异的衡量标准在冬季较高。我们还发现地下水片脚类动物可能在春季栖息的北极红点鲑的冬季饮食中发挥重要作用。总之，无脊椎动物群落的季节性变化是一个需要考虑的重要因素，并且有可能改变较高营养水平的表型（例如增长率）和行为（例如摄食偏好）。当猎物可用性较低时，作为种群内生态位变异量度的个体专业化在冬季较高。我们还发现地下水片脚类动物可能在春季栖息的北极红点鲑的冬季饮食中发挥重要作用。总之，无脊椎动物群落的季节性变化是一个需要考虑的重要因素，并且有可能改变较高营养水平的表型（例如增长率）和行为（例如摄食偏好）。当猎物可用性较低时，作为种群内生态位变异量度的个体专业化在冬季较高。我们还发现地下水片脚类动物可能在春季栖息的北极红点鲑的冬季饮食中发挥重要作用。总之，无脊椎动物群落的季节性变化是一个需要考虑的重要因素，并且有可能改变较高营养水平的表型（例如增长率）和行为（例如摄食偏好）。