The interaction between predation risk and food ration on behavior and morphology of Eurasian perch

Abstract

The risk of both predation and food level has been shown to affect phenotypic development of organisms. However, these two factors also influence animal behavior that in turn may influence phenotypic development. Hence, it might be difficult to disentangle the behavioral effect from the predator or resource‐level effects. This is because the presence of predators and high resource levels usually results in a lower activity, which in turn affects energy expenditure that is used for development and growth. It is therefore necessary to study how behavior interacts with changes in body shape with regard to resource density and predators. Here, we use the classic predator‐induced morphological defense in fish to study the interaction between predator cues, resource availability, and behavioral activity with the aim to determine their relative contribution to changes in body shape. We show that all three variables, the presence of a predator, food level, and activity, both additively and interactively, affected the body shape of perch. In general, the presence of predators, lower swimming activity, and higher food levels induced a deep body shape, with predation and behavior having similar effect and food treatment the smallest effect. The shape changes seemed to be mediated by changes in growth rate as body condition showed a similar effect as shape with regard to food‐level and predator treatments. Our results suggests that shape changes in animals to one environmental factor, for example, predation risk, can be context dependent, and depend on food levels or behavioral responses. Theoretical and empirical studies should further explore how this context dependence affects fitness components such as resource gain and mortality and their implications for population dynamics.

Predation selects for smaller eye size in a vertebrate: effects of environmental conditions and sex

“…However, we did not find an effect of resource level in the plasticity experiment, which suggests that at least under the resource levels we used this explanation is not valid. Perch did however grow in our experiment since an increase in body condition and plasticity in body shape as an effect of food in our 10-week experiment was found [28]. A second explanation could be that females experience other types of benefits of having large eyes, e.g.…”

“…Because of mortality in some of the aquaria, we were left with one to three fish per aquarium (total 82 individuals, average 2.3 fish per replicate) at the end of the experiment. There was no effect of treatment on mortality [28] nor was there an effect of mortality on eye size ( p ¼ 0.493). The amount of food supplied was adjusted according to the number of live fish per aquarium.…”

“…To investigate the effects of predator presence and food ration on eye size plasticity in perch we used data from Svanbäck et al [28]. In this experiment we used 1-year-old perch (79.3 + 4.5 mm, 4.4 + 1.0 g, mean fish length and weight + s.d.)…”

Temporal instability of lake charr phenotypes: synchronicity of growth rates and morphology linked to environmental variables?

“…Growth rate in fishes has been shown to drive intraspecific morphological differentiation (Tonn et al 1994;Olsson et al 2007;Chivers et al 2008). Growth rate seems to play a key role in regulating morphological expression, but underlying mechanisms remain uncertain (Olsson et al 2006;Svanbäck et al 2017;Franklin et al 2018). A possible explanation is that at higher growth rates, energy is allocated to somatic growth and morphology modulation in addition to metabolic maintenance, but that at lower growth rates, energy is used almost exclusively for metabolic maintenance and/or reproduction (Olsson et al 2006;Svanbäck et al 2017).…”

“…Growth rate seems to play a key role in regulating morphological expression, but underlying mechanisms remain uncertain (Olsson et al 2006;Svanbäck et al 2017;Franklin et al 2018). A possible explanation is that at higher growth rates, energy is allocated to somatic growth and morphology modulation in addition to metabolic maintenance, but that at lower growth rates, energy is used almost exclusively for metabolic maintenance and/or reproduction (Olsson et al 2006;Svanbäck et al 2017). Our results concur with this latter mechanism because lake charr sampled in 2007 had higher annual growth rates and less morphological overlap between ecotypes than lake charr sampled in 2018.…”