Abstract

Territoriality is thought to play an important role in the population regulation of animals. Consequently, the factors that affect territory size will also affect the number of individuals that can settle in a particular habitat. The prior-resident-advantage hypothesis predicts that territories will be smaller and more numerous in areas where individuals arrive synchronously rather than asynchronously, due to the dominance of residents over newcomers. I tested this prediction in a laboratory study with juvenile rainbow trout ( Oncorhynchus mykiss ). Although there was some evidence that early arrivers were more aggressive than late arrivers, there was no strong evidence that settlement pattern has an effect on the number and size of territories. In juvenile salmonid fishes, individual growth rate typically decreases with increasing density in observational field studies and territory size typically decreases with density in experimental laboratory studies. The validity of these studies has been questioned, because cause and effect cannot be inferred from the field studies and experimental laboratory studies are often unrealistic. To address the shortcomings of both approaches, I performed a field-based experiment using juvenile Atlantic salmon ( Salmo salar ) at Catamaran Brook, New Brunswick. I manipulated the density of salmon in mesh enclosures, while measuring the growth rate and territory size of the salmon. As predicted, both growth rate and territory size decreased with increasing density, providing strong support for previous studies