Prey eyes vs predator eyes4/3/2024 found that the relative eye size of fish was significantly smaller in high predation sites compared to low predation sites. However, predation risk and light intensity might interact. Organisms that live under low light intensity generally have larger eyes, which may be due to the fact that large eyes are usually more effective in absorbing light. Since food availability and predators covary in nature it is important to examine the interaction between these two factors, but unfortunately few such studies have been performed, although see Beston et al. Resource availability has been shown to affect eye size in animals: because eyes are costly to produce and maintain they are usually smaller when food availability is low. In general, the presence of predators causes an increase in food availability through a trophic cascade for the surviving prey individuals, and thus an increase in per capita food availability. In addition to the direct predation effects on eye size, the presence of predators has been shown to alter the food available to prey, which can have indirect consequences on prey eye size. Studies at the micro-evolutionary scale such as selection experiments are therefore needed to obtain a mechanistic understanding of eye size evolution. ) providing only indirect evidence for selection on eye size. In addition, the majority of studies investigating the drivers of eye size evolution have used a comparative approach (e.g. However, it could also be due to trade-offs with foraging efficiency, predator avoidance efficiency, or size difference between predator and prey. The difference between these conclusions could be due to differences in eye morphology among the study organism used, where for example, compound eyes and camera eyes have different morphology. In the former case, the explanation was that smaller eyes are less conspicuous and might reduce predation risk, and the latter case larger eyes were suggested to facilitate detection of potential predators. found a decrease in eye size in high predation environments while Glazier & Deptola found the opposite pattern. For example, Zaret & Kerfoot and Beston et al. While the observed variation in eye size among and within species has been suggested to be a result of natural selection, few studies have used an experimental approach to demonstrate that natural selection can cause shifts in eye size (but see ).Īt the moment, there is no consensus regarding how predation risk affects eye size. In addition, there is strong support that abiotic factors such as light availability also affect eye size evolution. Both predation risk and foraging efficiency have been suggested to be two major biological drivers of this variation. Our experiments provide evidence that predation risk could be one of the driving factors behind variation in eye size within species.Īnimals show large variation in relative eye size both within and among species. In the plasticity experiment, we found that fish predators induced smaller eye size in males, but not in females, while resource levels had no effect on eye size plasticity. In the first experiment, we found that habitat altered selection due to predators, since predators selected for smaller eye size in a non-vegetated habitat, but not in a vegetated habitat. Second, we studied the effects of both predation risk and resource levels on phenotypic plasticity in relative eye size in indoor aquaria experiments. First, we used large outdoor tanks to compare selection due to predators on relative eye size in open and artificial vegetated habitats. In this study, we address how predation affects variation in eye size by performing two experiments using Eurasian perch juveniles as prey and either larger perch or pike as predators. On the other hand, eyes are usually very conspicuous and several studies have suggested that eye size is associated with predation risk. Thus, larger eyes should aid both in finding food as well as detecting predators. Increased eye size in animals results in a larger retinal image and thus improves visual acuity.
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