The Effect of Food Abundance on Territory Size and Population Density of Juvenile Steelhead Trout (Oncorhynchus mykiss)

• Published in: Oecologia Vol. 138; no. 3; pp. 371 - 378
• Main Authors: Imre, I., Grant, J. W. A., Keeley, E. R.
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-02-2004; Springer; Springer Nature B.V
• Subjects: Agnatha. Pisces; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Biomass; Body Constitution; Body size; Colonies & territories; Demecology; Density; Diet; Emigration; Female; Fish; Food; Food availability; Food Chain; Food Deprivation; Food supply; Freshwater; Fundamental and applied biological sciences. Psychology; Local population; Male; Mortality; Oncorhynchus mykiss; Oncorhynchus mykiss - growth & development; Population density; Population Dynamics; Population Ecology; Salmon; Stream channels; Territoriality; Trout; Vertebrata; Young animals; Salmonidae; Territory; Population number; Environmental factor; Biomass; Oncorhynchus mykiss; Young animal; Contiguous territory; Vertebrata; Pisces; Juvenile salmonids; Population dynamics; Food supply; Population density; Ecological abundance
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-003-1432-z

Optimal territory size models predict a decrease in territory size with increasing food abundance. However, most of these models may not be applicable to juvenile salmonids in streams, because they defend contiguous territories at high densities. The optimal size of a contiguous territory is predicted to (1) be independent of food abundance when food is rare and (2) decrease only when food abundance is high enough to induce a reduction in territory size below the contiguous optimum. To test these predictions, we raised equal densities of juvenile steelhead trout in outdoor stream channels over a 32-fold range of food abundance in the absence of emigration for 25 days. Increasing competition for scarce food resulted in increasing mortality, higher willingness to emigrate, higher variance in body mass, lower growth, lower population density and lower biomass. The size of territories decreased with increasing local population density, and increased with increasing body size. However, territory size did not change with food abundance, a result consistent with the prediction of a contiguous territory size model. On average, total salmonid biomass increased 5.7 times in response to the 32-fold increase in food abundance. Our data provide strong support for an earlier quantitative relationship between the abundance of stream salmonids and their food.