The shape of pupils could provide significant advantages to predators and prey out in the wild, a new study concludes. Needs of the animal could dictate whether the species has vertical or horizontal pupils, investigators determined.
Predators, such as cats, possess vertical pupils, which results in out-of-focus areas in the animal's line of sight. Horizontal objects, such as prey animals, go out of focus as they become more distant. The creatures then use this effect as a tool for determining the distance to potential prey.
Vertical slits in eyes can alter the amount of light entering their aperture far more than round pupils like those found in humans are able to do. While pupils of our own species are able to alter in size 15 times in brightest to darkest light conditions, cats have a 135-fold growth. In geckos, that number is 300 times.
Researchers speculate that horizontal pupils seen in many prey animals could provide a panoramic view, allowing the creatures to scan a greater range of their territory for predators. Having a horizontal rectangle for a pupil can also provide the creatures a superior ability to see "out of the corner" of their eye. This would allow them to see obstacles in front of them, such as rocks, as they pounce for a sprint after spotting a predator coming up behind them. They may also provide a form of shade, shielding the creatures from glaring overhead light.
Computer simulations were performed for different eye models, providing investigators with a means of accurately measuring how various animals view the world.
Biologists had long ago realized that most predators feature eyes placed on the front of their faces, while prey animals normally have eyes on the sides of their heads. These placements are designed to give the predator an advantage when judging distance, and provides target animals with a wider field of view.
Biologists, however, caution that these generalizations should not be misconstrued to mean that pupil shape accurately determines the feeding habits of a particular species.
"For species that are active both night and day, like domestic cats, slit pupils provide the dynamic range needed to help them see in dim light yet not get blinded by the midday sun. However, this hypothesis does not explain why slits are either vertical or horizontal. Why don't we see diagonal slits? This study is the first attempt to explain why orientation matters," Martin Banks of the University of California Berkeley said.
Examination of the visual qualities of differing pupil shapes in the predators and prey animals was published in the journal Science Advances.
Photo: Kayla Kandzorra | Flickr