The fish community of Lake Constance, a large, deep, oligotrophic lake has undergone drastic changes in recent years, with the sudden rise to dominance of invasive three-spined stickleback (Gasterosteus aculeatus) in the pelagic zone, a rather atypical habitat for this species in Central Europe. The core objective of this study was to compare the feeding ecology of stickleback and young Eurasian perch (Perca fluviatilis) in this unique situation to identify reasons for this unexpected dominance, a possible food niche and feeding time overlap, and to discuss consequences for the reshaped pelagic fish community. The diel feeding patterns and prey compositions of pelagic sticklebacks and juvenile (0+) perch sampled in October 2018 and March 2019 were studied analyzing stomach contents. The diets of both species mostly comprised zooplankton, with copepods appearing in the greatest numbers. Benthic and airborne insects were consumed occasionally, mostly by sticklebacks. Both species exhibited peaks of feeding activity early in the morning, afternoon and dusk, and in both species, stomachs were fullest at dusk. Stickleback stomachs contained about 20 % more prey at night than perch, and mean estimated nocturnal stomach fullness values were almost 50 % greater. Night feeding in sticklebacks was confirmed by digestive states, pointing to a possible competitive advantage over perch. Dietary composition varied over a 24-h cycle and the pattern of consumption of different prey varied between the species. Perch consumed more comparatively small cladocerans (Bosmina spp.), while larger Daphnia appeared more often in stickleback stomachs. In both species, seasonal variation in diet mirrored food availability, indicating some degree of opportunism. A Morisita-Horn index value of 0.95 confirmed dietary niche overlap between species, suggesting the large population of sticklebacks may exert a competitive effect on juvenile perch when resources are limited. Both the longer feeding periods and greater intake of nutritive high quality prey like daphnids can contribute to the rapid success of stickleback in dominating the pelagic zone of Lake Constance.

中文翻译：

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康斯坦茨湖上层浮游带与原生欧亚鲈鱼幼鱼（Perca fluviatilis）相关的入侵三刺棘鱼（Gasterosteus aculeatus）的摄食生态

康斯坦茨湖的鱼类群落是一个大而深的贫营养湖泊，近年来发生了剧烈的变化，在远洋区入侵的三刺棘鱼 (Gasterosteus aculeatus) 突然占据主导地位，这是该物种的一个非典型栖息地在中欧。本研究的核心目标是在这种独特情况下比较棘鱼和幼年欧亚鲈鱼 (Perca fluviatilis) 的摄食生态，以确定这种意想不到的优势、可能的食物生态位和摄食时间重叠的原因，并讨论对重新塑造的鲈鱼的影响远洋鱼类群落。通过分析胃内容物，研究了 2018 年 10 月和 2019 年 3 月采样的远洋棘鱼和幼鱼 (0+) 鲈鱼的日食模式和猎物组成。这两个物种的饮食主要包括浮游动物，桡足类出现的数量最多。偶尔食用底栖和空气传播的昆虫，主要是刺鱼。这两个物种在清晨、下午和黄昏都表现出摄食活动的高峰，并且在这两个物种中，黄昏时胃最饱满。刺鱼在夜间的价格比鲈鱼高出约 20%，夜间胃饱腹度的平均估计值高出近 50%。消化状态证实了刺鱼夜间进食，这表明它可能比鲈鱼具有竞争优势。膳食成分在 24 小时周期内变化，不同价格的消费模式因物种而异。鲈鱼消耗更多相对较小的枝角类动物（Bosmina spp.），而较大的水蚤则更常出现在刺鱼的胃中。在这两个物种中，饮食的季节性变化反映了食物供应情况，表明存在某种程度的机会主义。Morisita-Horn 指数值为 0.95，证实了物种之间的饮食生态位重叠，这表明当资源有限时，大量棘鱼可能对幼鲈产生竞争影响。更长的摄食期和更多的营养优质猎物（如水蚤）的摄入量都有助于刺鱼在博登湖的远洋区迅速取得成功。