Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems

1. Clark & Levy (1988) described an antipredation window for smaller planktivorous fish during crepuscular periods when light permits feeding on zooplankton, but limits visual detection by piscivores. Yet, how the window is influenced by the interaction between light regime, turbidity and cloud cover over a broad latitudinal gradient remains unexplored. 2. We evaluated how latitudinal and seasonal shifts in diel light regimes alter the foraging-risk environment for visually-feeding planktivores and piscivores across a natural range of turbidities and cloud covers. Pairing a model of aquatic visual feeding with a model of sun and moon illuminance, we estimated foraging rates of an idealized planktivore and piscivore over depth and time across factorial combinations of latitude (0-70º), turbidity (0.1-5 NTU) and cloud cover (clear to overcast skies) during the summer solstice and autumnal equinox. We evaluated the foraging-risk environment based on changes in the magnitude, duration a...

1. Clark与Levy（1988）曾提出，小型浮游食性鱼类（planktivorous fish）存在反捕食窗口（antipredation window）：在晨昏时段，光线条件既允许其捕食浮游动物（zooplankton），又可限制食鱼性捕食者（piscivores）的视觉探测能力。然而，在宽纬度梯度范围内，该窗口如何受光照节律（light regime）、浊度（turbidity）与云量（cloud cover）的交互作用调控，目前仍有待探索。2. 本研究旨在探究昼夜光照节律（diel light regimes）的纬度与季节偏移，如何在自然浊度与云量区间内，改变视觉摄食型浮游食性鱼类与食鱼性捕食者所面临的觅食-风险环境。我们将水生视觉摄食模型与日月光照度模型相结合，在夏至（summer solstice）与秋分（autumnal equinox）两个关键时间节点，针对纬度（0°~70°）、浊度（0.1~5 NTU）与云量（晴空至阴天）的全因子组合，估算了理想化浮游食性鱼类与食鱼性捕食者在不同深度与时段的觅食速率。我们基于强度、持续时长及后续截断内容的变化评估了该觅食-风险环境。