Is the shape of the density–growth relationship for stream salmonids evidence for exploitative rather than interference competition?
Article first published online: 24 OCT 2006
Journal of Animal Ecology
Volume 76, Issue 1, pages 135–138, January 2007
How to Cite
WARD, D. M., NISLOW, K. H., ARMSTRONG, J. D., EINUM, S. and FOLT, C. L. (2007), Is the shape of the density–growth relationship for stream salmonids evidence for exploitative rather than interference competition?. Journal of Animal Ecology, 76: 135–138. doi: 10.1111/j.1365-2656.2006.01169.x
- Issue published online: 24 OCT 2006
- Article first published online: 24 OCT 2006
- Received 20 April 2006; accepted 11 August 2006
- density dependence;
- intraspecific competition;
- territorial competition
- 1Empirical studies show that average growth of stream-dwelling salmon and trout often declines with increasing density in a characteristic concave relationship. However, the mechanisms that generate negative density–growth relationships in populations in natural streams are not certain.
- 2In a recent study, Imre, Grant & Cunjak (2005; Journal of Animal Ecology, 74, 508–516) argue that density-dependent growth due to exploitative competition for prey causes the negative density–growth relationships for stream salmonids. They argue that the concave shape of empirical density–growth relationships is consistent with a simple model of exploitative competition and not consistent with interference competition for space.
- 3We use a simple model to show that competition for space can yield concave density–growth relationships consistent with the empirical pattern when individuals compete for foraging sites that vary spatially in quality and lower-quality sites predominate. Thus, the predictions of the exploitative competition and spatial competition models overlap.
- 4The shape of the density–growth relationship does not differentiate between candidate mechanisms underlying density-dependent growth for stream salmonids. Our results highlight the general problem with determining the mechanism driving an ecological process from patterns in observational data within the context of linking population demographics to habitat structure and animal behaviour.