Density-dependent diel activity in stream-dwelling Arctic charr Salvelinus alpinus

Intraspecific competition plays a significant role in shaping how animals use and share habitats in space and time. However, the way individuals may modify their diel activity in response to increased competition has received limited attention. We used juvenile (age 1+) Arctic charr Salvelinus alpinus to test the prediction that individuals at high population density are more active and distribute their foraging activity over a greater portion of the 24-h cycle than individuals at low population density. Individually tagged fish were stocked in seminatural stream enclosures at low (2 fish/m2) and high (6 fish/m2) density. During each of two 2-week experimental rounds, activity of all fish within each enclosure was recorded every 3 h over seven 24-h cycles. At high density, fish were more active and distributed their activity over a greater portion of the 24-h cycle, with increased activity particularly at crepuscular times. Fluctuations in ecological conditions (e.g., water temperature ...种内竞争（intraspecific competition）在塑造动物时空维度上的栖息地利用与共享格局中发挥着关键作用。然而，个体针对竞争加剧调整其昼夜活动（diel activity）的方式，却鲜有研究予以关注。本研究以1龄以上的幼年北极红点鲑（Salvelinus alpinus）为实验材料，验证如下预测：相较于低密度种群个体，高密度种群个体的活动更为频繁，且其觅食活动在24小时周期内的分布时段更广。将经个体标记的实验鱼以低密度（2尾/平方米）与高密度（6尾/平方米）两种密度放养于半自然溪流围笼（seminatural stream enclosures）中。在两轮为期两周的实验周期内，每3小时对每个围笼内所有实验鱼的活动进行一次记录，连续覆盖7个24小时周期。结果显示，高密度组的实验鱼活动更为频繁，且其活动在24小时周期内的分布时段更广，尤其在晨昏时段的活动显著提升。生态条件的波动（如水温……