Regional analysis of body size and population density in stream fish assemblages: testing predictions of the energetic equivalence rule

• Published in: Canadian journal of fisheries and aquatic sciences 2002-08, Vol.59 (8), p.1350-1360
• Main Author: Knouft, Jason H
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal body; Animal populations; Animal, plant and microbial ecology; Biological and medical sciences; Body size; Creeks & streams; Distribution; Fish; Fish populations; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Marine ecosystems; Physical growth; Population density; Regional analysis; Regional planning; Size; Synecology
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f02-110

The energetic equivalence rule predicts that body mass (W) and population density ( β) within an assemblage are negatively correlated and will exhibit a W –0.75 = β relationship. Bergmann's rule predicts that body size among species will increase with increasing latitude. If species body size increases with latitude, the shape of the body size – population density distribution among assemblages may also vary. This change in the body size – population density distribution, when viewed in the context of the energetic equivalence rule, may indicate an alteration in the use of available energy by individuals of different sizes within an assemblage. Twenty-eight streams were sampled across four geographically distinct regions to determine if stream fish assemblages conform to the prediction of the energetic equivalence rule. Body size in stream fish assemblages did not support the pattern predicted by Bergmann's rule, but rather was negatively correlated with latitude. Stream fish assemblages generally did not conform to the relationship predicted by the energetic equivalence rule. Moreover, these results, coupled with the predictions of the energetic equivalence rule, suggest that larger individuals tended to control a disproportionately greater amount of energy than smaller individuals in stream fish assemblages, which may be partially due to predation pressure on smaller individuals.