Data from: 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 and light intensity) also affected activity. Fish at high density grew as fast as fish at low density. This study demonstrates that individuals exhibit a degree of behavioral flexibility in their response to changes in ecological conditions and suggests that intraspecific competition can cause animals to modify temporal aspects of their activity to gain access to resources and maintain growth.种内竞争（Intraspecific competition）在塑造动物在时空维度对栖息地的利用与共享模式中发挥着重要作用。不过，个体为应对竞争加剧而调整其昼夜活动（diel activity）的方式，却尚未得到充分关注。本研究以1龄及以上的幼体北极红点鲑（Salvelinus alpinus）为实验对象，验证如下预测：相较于低种群密度环境中的个体，高种群密度下的北极红点鲑会表现出更高的活动水平，且其觅食活动在24小时周期内的分布时段更广。我们将个体标记后的实验鱼放养于低（2尾/平方米）和高（6尾/平方米）两种种群密度的半天然溪流围笼中。在两轮各为期2周的实验中，我们于7个完整的24小时周期内，每隔3小时记录每个围笼内所有实验鱼的活动情况。结果显示，高种群密度下的实验鱼活动水平更高，且活动在24小时周期内的分布时段更广，其活动峰值尤其出现在晨昏时段。生态条件（如水温与光照强度）的波动同样会对实验鱼的活动产生影响。高种群密度下的实验鱼生长速率与低种群密度组并无显著差异。本研究证实，动物在应对生态条件变化时具备一定的行为可塑性；同时表明种内竞争可促使动物调整其活动的时间特征，以获取资源并维持正常生长。