Shape of Single and Multiple Central-Place Territories in aStream-Dwelling Fish

摘要

Territory shape yields important insights into how animals exploit localresources. Territories of stream-dwelling salmonids are typically (1)mapped around a single central-place, (2) described as circular, ellipticalor teardrop-shaped, and (3) believed to reflect their exploitation ofdrifting invertebrate prey. In this study, we tested the current view ofterritory shape by mapping multiple central-place territories for 50young-of-the-year Atlantic salmon. Multiple central-place areas weremore elongated (eccentricity: median = 1.301, range = 1.043–2.784)than the foraging patterns around each central place (eccentricity: median = 1.135, range = 1.014–1.385). In addition, multiple central-place areas were elongated along the stream length (33 of 50 fish), whereasthe foraging areas around each station tended to be elongated along thestream width (32 of 50 fish). These findings may be explained by theway that stream salmonids interact with drifting prey. At each centralplace, a wider foraging area should provide an increased access to preydrifting downstream. Similarly, by regularly patrolling a large multiplecentral-place area along the stream axis, a territorial fish may increaseits access to drifting prey by excluding competitors from upstream areas.Further studies are needed on the ecological factors that determine territory shape in stream fish and multiple central-place foragers.