title: Density-dependent diel activity in stream-dwelling Arctic charr Salvelinus alpinus.
abstract: 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/m(2)) and high (6 fish/m(2)) 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.
authors.affiliation: Department of Aquaculture and Fish Biology Hólar University College Sauðárkrókur Iceland.
authors.forename: Amy
authors.initials: A
authors.lastname: Fingerle
authors.affiliation: Department of Aquaculture and Fish Biology Hólar University College Sauðárkrókur Iceland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Larranaga
authors.affiliation: Department of Aquaculture and Fish Biology Hólar University College Sauðárkrókur Iceland.
authors.forename: Stefán Óli
authors.initials: SÓ
authors.lastname: Steingrímsson
keywords: Activity rate; resource partitioning; rivers; salmonids; temporal segregation