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.

种内竞争在塑造动物时空维度上的栖息地利用与共享模式中发挥着关键作用。然而，个体如何响应竞争加剧而调整其昼夜活动节律，这一问题迄今尚未得到充分关注。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：种群密度较高的个体相较于低密度个体，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。研究中将佩戴个体标记的实验鱼分别以低密度（2尾/平方米）与高密度（6尾/平方米）的密度放养于半天然溪流围栏内。在两轮各为期2周的实验轮次中，每轮连续7个24小时周期内，每3小时记录一次每个围栏内所有实验鱼的活动情况。结果显示，高密度组的实验鱼活动更为频繁，且其活动在24小时周期内的覆盖时段更广，尤其在晨昏时段的活动量显著提升。生态条件（如水温和光照强度）的波动同样会对鱼类活动产生影响。高密度组实验鱼的生长速率与低密度组无显著差异。本研究表明，动物在响应生态条件变化时具备一定的行为可塑性；同时也揭示，种内竞争可促使动物调整其活动的时间模式，以获取资源并维持生长。