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Bentuk pupil  terkait dengan niche ekologi hewan 

Date:

August 7, 2015

Source:

University of California - Berkeley

Summary:

Niche ekologi hewan ' adalah prediktor kuat dari bentuk pupil , analisis baru telah ditemukan . Spesies dengan pupil  yang celah vertikalnya  lebih cenderung menjadi predator penyergapan yang aktif baik siang dan malam . Sebaliknya , mereka  dengan pupil  horizontal memanjang sangat mungkin spesies pemakan  tanaman - dengan mata di sisi kepala mereka .

................... Analisis 214 spesies hewan darat menunjukkan bahwa niche ekologi  adalah prediktor kuat dari bentuk pupil . Spesies dengan pupil  yang celah vertikalnya   cenderung lebih  menjadi predator penyergapan yang aktif baik siang dan malam . Sebaliknya , mereka  dengan pupil  horizontal memanjang sangat mungkin spesies pemakan tanaman - dengan mata di sisi kepala mereka . pupil melingkar yang terkait dengan " pemburu aktif , " atau hewan yang mengejar mangsanya .....more

Pupil shape
linked to animals' ecological niche

Date:

August 7, 2015

Source:

University of California - Berkeley

Summary:

A land animals' ecological niche is a strong predictor of pupil shape, a
new analysis has found. Species with pupils that are vertical slits are more
likely to be ambush predators that are active both day and night. In contrast,
those with horizontally elongated pupils are extremely likely to be
plant-eating prey species with eyes on the sides of their heads.

...................

While the eyes may be a window into one's soul, new research led by
scientists at the University of California, Berkeley, suggests that the pupils
could also reveal whether one is a hunter or hunted.

An analysis of 214 species of land animals shows that a creature's
ecological niche is a strong predictor of pupil shape. Species with pupils that
are vertical slits are more likely to be ambush predators that are active both
day and night. In contrast, those with horizontally elongated pupils are
extremely likely to be plant-eating prey species with eyes on the sides of
their heads. Circular pupils were linked to "active foragers," or
animals that chase down their prey.

The study, led by vision scientist Martin Banks, a UC Berkeley professor of
optometry, in collaboration with the United Kingdom's Durham University,
presents a new hypothesis as to why pupils are shaped and oriented the way they
are. The findings will be published in the journal Science Advances.

This current research builds upon the foundation set by the late Gordon
Walls, a UC Berkeley professor of optometry who published "The Vertebrate
Eye and Its Adaptive Radiation" in 1942. The classic text on eye
physiology put forward the theory, generally accepted, that slit-shaped pupils
allow for different musculature and a greater range in the amount of light
entering the eye.

For example, the vertical slits of domestic cats and geckos undergo a 135-
and 300-fold change in area between constricted and dilated states, while
humans' circular pupils undergo a mere 15-fold change.

Why not diagonal slits?

"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," said Banks. "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."

To explain why horizontally elongated pupils, with few exceptions(are there
any explanations for the exceptions?), corresponded to grazing prey animals
such as sheep, deer and horses, the researchers turned to computer models to
study the effects of different pupil shapes.

They found that the horizontal pupils expanded the effective field of view.
When stretched horizontally, the pupils are aligned with the ground, getting
more light in from the front, back and sides. The orientation also helps limit
the amount of dazzling light from the sun above so the animal can see the
ground better, the researchers said.

"The first key visual requirement for these animals is to detect
approaching predators, which usually come from the ground, so they need to see
panoramically on the ground with minimal blind spots," said Banks.
"The second critical requirement is that once they do detect a predator,
they need to see where they are running. They have to see well enough out of
the corner of their eye to run quickly and jump over things."

But what happens to this orientation when the animal lowers its head to
graze? If the pupil follows the pitch of the head, they would become more
vertical and the theory falters.

"To check this out, I spent hours at the Oakland Zoo, often surrounded
by school kids on field trips, to observe the different animals," said
Banks. "Sure enough, when goats, antelope and other grazing prey animals
put their head down to eat, their eyes rotated to maintain the pupils'
horizontal alignment with the ground."

On the other side of the Atlantic, study co-author Gordon Love, a professor
of physics at Durham University, found this same pattern when observing sheep
and horses at nearby farms. Grazing animals' eyes can rotate by 50 degrees or
more in each eye, a range 10 times greater than human eyes, the researchers
said.

How ambush predators focus when catching prey

For ambush predators with vertical-slit pupils, the authors noted the
importance of accurately gauging the distance animals would need to pounce on
their prey. Researchers identified three cues generally used to gauge distance:
stereopsis, or binocular disparity; motion parallax, in which closer objects
move farther and faster across our field of vision; and blur, in which objects
at different distances are out of focus.

The researchers ruled out motion parallax as a factor since using that cue
would require head movement that could reveal the predator's position. The
remaining two cues, binocular disparity and blur, work together with vertically
elongated pupils and front-facing eyes, the researchers said.

Binocular vision works better at judging differences when contours are
vertical and objects are at a distance, while blur comes into play for
horizontal contours and near-field targets. Vertical-slit pupils maximize both
cues, the researchers said.

Vertical pupils are not equally distributed among ambush predators,
however.

"A surprising thing we noticed from this study is that the slit pupils
were linked to predators that were close to the ground," said William
Sprague, a postdoctoral researcher in Banks' lab. "So domestic cats have
vertical slits, but bigger cats, like tigers and lions, don't. Their pupils are
round, like humans and dogs."

Among the 65 frontal-eyed, ambush predators in this study, 44 had vertical
pupils, and 82 percent of them had shoulder heights that were less than 42
centimeters (16.5 inches). Vertical pupils appear to maximize the ability of
small animals to judge distances of prey.

The authors explained this by calculating that depth-of-field cues based
upon blur are more effective for estimating distances for short animals than
tall ones.

"We are learning all the time just how remarkable the eye and vision
are," said Love. "This work is another piece in the jigsaw puzzle of
understanding how eyes work."

The authors noted that this research focused on terrestrial species. They
expect to examine associations of aquatic, aerial and arboreal life on eye
position and pupil shape in future studies.







Story Source:

The above post is reprinted from materials provided byUniversity
of California - Berkeley. The original item was written by Sarah
Yang. Note: Materials may be edited for content and length.







Journal Reference:

1.   
Martin S. Banks, William W. Sprague, Jürgen Schmoll, Jared A. Q. Parnell
and Gordon D. Love. Why do animal eyes have pupils of different shapes? Science
Advances, August 2015 DOI: 10.1126/sciadv.1500391

http://www.sciencedaily.com/releases/2015/08/150807144334.htm

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