Journal of Animal Ecology 2007 76, 149–158 © 2006 The Authors. Journal compilation © 2006 British Ecological Society Blackwell Publishing Ltd Intraspecific competition and density dependence of food consumption and growth in Arctic charr PER-ARNE AMUNDSEN, RUNE KNUDSEN and ANDERS KLEMETSEN Department of Aquatic BioSciences, Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway Summary 1. Intraspecific competition for restricted food resources is considered to play a funda- mental part in density dependence of somatic growth and other population characteristics, but studies simultaneously addressing the interrelationships between population density, food acquisition and somatic growth have been missing. 2. We explored the food consumption and individual growth rates of Arctic charr Salvelinus alpinus in a long-term survey following a large-scale density manipulation experiment in a subarctic lake. 3. Prior to the initiation of the experiment, the population density was high and the somatic growth rates low, revealing a severely overcrowded and stunted fish population. 4. During the 6-year period of stock depletion the population density of Arctic charr was reduced with about 75%, resulting in an almost twofold increase in food consumption rates and enhanced individual growth rates of the fish. 5. Over the decade following the density manipulation experiment, the population density gradually rose to intermediate levels, accompanied by corresponding reduc- tions in food consumption and somatic growth rates. 6. The study revealed negative relationships with population density for both food consumption and individual growth rates, reflecting a strong positive correlation between quantitative food intake and somatic growth rates. 7. Both the growth and consumption rate relationships with population density were well described by negative power curves, suggesting that large density perturbations are necessary to induce improved feeding conditions and growth rates in stunted fish populations. 8. The findings demonstrate that quantitative food consumption represents the con- nective link between population density and individual growth rates, apparently being highly influenced by intraspecific competition for limited resources. Key-words: competitive interactions, feeding, freshwater fish, population abundance, resource limitation. Journal of Animal Ecology (2007), 76, 149–158 doi: 10.1111/j.1365-2656.2006.01179.x Introduction Food acquisition provides the necessary energy for life maintenance, growth and reproduction of living organ- isms and is instrumental in the ecology and evolution of animal populations. Food availability may, however, be restricted, resulting in competitive interactions for limited resources (e.g. Keddy 1989). As individuals within the same species have highly similar resource requirements, the intensity of intraspecific competition is assumedly severe and strongly related to the popula- tion density. Intraspecific competition is furthermore expected to result in reduced resource acquisition and diminished individual growth and development rates, which in turn may lead to increased mortality rates. In mammals and birds with highly fixed and pre-determined individual growth and development trajectories mani- fested in, e.g. characteristic adult sizes, severe resource limitation and starvation may directly influence survival (Piatt & Pelt 1997; Mduma, Sinclair & Hilborn 1999; Keymer et al . 2001; Camphuysen et al . 2002; Reid & Forcada 2005). Fish and other organisms with a high Correspondence: Per-Arne Amundsen, Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway. E-mail: Per-Arne.Amundsen@nfh.uit.no