Risk-taking behaviour in foraging young-of-the-year perch varies with population size structure

Abstract

I investigated if risk-taking behaviour of young-of-the-year (YOY) perch Perca fluviatilis was connected with population-specific predation patterns in four lakes in northern Sweden. The lakes differ in perch size distribution, according to earlier fishing surveys. Thus, the most intense predation pressure by cannibals is assumed to occur at different prey-size windows in the four lakes. In an aquarium study, I observed groups of perch, and registered time spent foraging in an open habitat and number of prey attacks in the presence of a predator. Perch from Angersjön, with the highest proportion of large fish in the population, spent more time in the open area than those from Fisksjön that has a dense population of mainly small perch. The Angersjön perch also made more prey attacks than did perch from Fisksjön and Bjännsjön. Relative differences in predation risk in the four lakes were estimated as cannibalistic attack rates, on a range of sizes of YOY perch, calculated from population size distributions. Principal component analysis on predation risk patterns resulted in two components, of which PC1 explained 79.1% of the variation. High scores of PC1 indicated low cannibalistic attack rates on smaller perch (10-20 mm) and high rates on larger fish (> or =30 mm), while low scores indicated the opposite. The level of risk-taking behaviour in the aquarium study positively correlated with lake-specific PC1 scores. The perch with the most cautious behaviour in the aquaria originated from the population with the highest predation pressure on early stages. The boldest perch came from the lake with low predation on the smallest, but with higher predation on larger YOY perch. Thus, the influence of predation risk on behaviour patterns in perch may depend on the timing of the highest exposure to predators.

Behavioural variation in Eurasian perch populations with respect to relative catchability

“…throughout the experiment). Accordingly, bold individuals showing high risk-taking behaviour in the presence of predators often react by being less disturbed by predator presence, whereas shy individuals react to experienced predation risk by reducing their activity and seeking shelter (Sneddon 2003;Magnhagen 2006). However, the consistency of activity was found to be lower (16 % of the behavioural variation lied between the individuals) in comparison to boldness (44 %).…”

Development of abundance and size structure of young-of-the-year perch populations using three methods

“…Observed differences between the bongo net catches and electrofishing, and between electrofishing and gillnet samples in the gravel pit lakes, were assumed to depend partly on the different occurrence of different size classes of perch at the sampling locations, due either to time differences in the size-specific habitat shift or to smallscale differences where perch stay in the littoral zone. However, the observed differences between electrofishing and gillnet samples in the shallow experimental ponds presumably depend on differences in the activity level of small and large YOY perch, possibly forced by differential predation risk (Magnhagen, 2006;Heermann and Borcherding, unpublished results). While confirming preliminary studies (Wanzenböck et al, 1997;Tischler et al, 2000), our results offer additional evidence that at least two of the three methods used in this study should be applied in an overlapping and parallel sampling design, in order to be sure of obtaining all relevant data on the development of the size structure of the YOY perch population of interest.…”

Body size, temperature, and seasonal differences in size structure influence the occurrence of cannibalism in larvae of the migratory dragonfly, Anax junius

“…Overlap between year classes (Van Buskirk 1992), developmental asynchrony (Wissinger 1988b;Corbet 1999), cohort splitting (Johnson 1986;Gurney et al 1992Gurney et al , 1994Moreira and Peckarsky 1994;Johnson et al 1995), and phenological separation between cohorts (Trottier 1971;Wissinger 1988b;Corbet 1999) are only a few of the mechanisms that can generate variation in size among individuals in a population. There is considerable potential for cannibalism in size-structured populations of predators (Fox 1975;Polis 1981;Ebenman and Persson 1988;Wissinger 1992), but the size structure of populations may also vary considerably over space and time (Stein et al 1988;Blumenshine et al 2000;Magnhagen 2006). Cannibalism is most common in highly size-structured populations because predators tend to select prey based on body size (Dodson 1970;Thompson 1978;Werner and Gilliam 1984) and interactions between conspecifics that differ greatly in size are very likely under these conditions (Ebenman and Persson 1988).…”