Boldness in two perch populations - long-term differences and the effect of predation pressure.
1. Populations of the same species often display different behaviours, for example, in their response to predators. The question is whether this difference is developed as part of a divergent selection caused by differences in predation pressure, or as a result of phenotypic responses to current environmental conditions. 2. Two populations of Eurasian perch were investigated over a time span of 6 years to see whether risk-taking behaviour in young-of-the-year perch were consistent across cohorts, or if behaviour varied over time with changes in predation regime. 3. Boldness was estimated in aquarium studies by looking at how the fish made trade-offs between foraging in a risky area and staying in shelter. Predation risk of each year and lake was estimated from fishing surveys, using an individual-based model calculating attack rates for cannibalistic perch. 4. The average boldness scores were consistently lower in perch from Fisksjön compared with those in Ängersjön, although the magnitude of the difference varied among years. Variance component analyses showed that differences between lakes in boldness scores only explained 12 per cent of the total variation. Differences between years were contributing at least similarly or more to the total variance, and the variation was higher in Fisksjön than in Ängersjön. 5. The observed risk-taking behaviour of young-of-the-year perch, compared across cohorts, was significantly correlated with the year-specific estimates of cannibalistic attack rates, with lower boldness scores in years with higher predation pressure. In Fisksjön, with significant changes over the years in population structure, the range of both predation risk and boldness scores was wider than in Ängersjön. 6. By following the two perch populations over several years, we have been able to show that the differences in risk-taking behaviour mainly are due to direct phenotypic responses to recent experience of predation risk. Long-term differences in behaviour among perch populations thus reflect consistent differences in predation regime rather than diverging inherent traits.
Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
Carin
C
Magnhagen
Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
Gustav
G
Hellström
Department of General Ecology and Limnology, Zoological Institute of the University of Cologne, Ecological Field Station Grietherbusch, D-50923, Cologne, Germany.
Jost
J
Borcherding
Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.|Department of General Ecology and Limnology, Zoological Institute of the University of Cologne, Ecological Field Station Grietherbusch, D-50923, Cologne, Germany.
Martina
M
Heynen
D000818:Animals; D002190:Cannibalism; D004777:Environment; D005247:Feeding Behavior; D020387:Food Chain; D010471:Perches / Q000502:physiology*; D025341:Principal Component Analysis; D011897:Random Allocation; D012621:Seasons; D013548:Sweden