Size‐dependent foraging capacities and intercohort competition in an ontogenetic omnivore (Arctic char)

• Published in: Oikos
• Main Authors: Byström, Pär, Andersson, Jens
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2005
• Subjects: Arctic; The Hump; Salvelinus alpinus; Subarctic; Zooplankton
• Online Access: http://dx.doi.org/10.1111/j.0030-1299.2005.13543.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.0030-1299.2005.13543.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0030-1299.2005.13543.x

Intraspecific competition for resources is strongly influenced by the size of competitors. In this study, we estimated the size‐scaling of the foraging capacities on zooplankton and benthic macroinvertebrates in Arctic char ( Salvelinus alpinus ) to link size‐dependent performance to effects from competition. The competitive interactions between two size‐classes (YOY and 1‐y) of char were then studied in a large‐scale pond experiment and in two small subarctic lakes. The attack rate function on zooplankton was hump‐shaped whereas the attack rate on benthic chironomids increased monotonically with size. The size‐scaling exponent's for zooplankton and chironomids were 0.65 and 0.30, respectively, leading to that critical resource density (CRD) and maximum growth resource density (G M RD) increases with size, suggesting an exploitative competitive advantage of small individuals over large. Correspondingly, large (1‐y) char growth was negatively affected by cohort competition whereas small (YOY) char growth was not. Diets of both size classes were dominated by macroinvertebrates with large overlap in prey size suggesting only small gape size advantages for large char. Small char fed to a larger extend on cladocerans which, due to the hump‐shaped foraging efficiency function on zooplankton, were a relatively more profitable resource for small than large char. Estimates of CRD and G m RD were in correspondence with observed growth responses and resource estimates for zooplankton, whereas for macroinvertebrates only qualitatively correspondence with foraging estimates and char performance was found. Although we were able to explain our results with exploitative competition only, we suggest a general need for size‐dependent foraging estimates on prey in more complex habitats in order to quantitatively link performance and resource abundances. Interference and size‐dependent resource use as mechanisms for observed stable population dynamics in char was not supported by this study and instead a low per capita fecundity ...