San Francisco State University
Geography 316: Biogeography
The Biogeography of the Polar Bear (Ursus maritimus)
by Emile G. Janicot, student in Geography 316, Fall 1999
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Genus: Ursus
Species: Ursus maritmus
Common names: White Bear, Water Bear, Ice Bear, Sea Bear.
Description of Species
Polar bears are the largest of all bears. They have adapted from the
size of a small dog to a carnivore that can look an elephant in the eye when standing on
their hind legs. Most males are slightly larger than the females, and range in size from
600 pounds to 1500 pounds. The paws of these bears range from 8 inches to 15 inches
across. These bears are very agile hunters, swimmers, climbers, and runners. With such
powerful bodies, these bears are the primary carnivores in the Arctic. The layer of dense
fur that covers these bears ranges from two inches to 6 inches in length. The skin of
these bears is actually black at the surface to catch all of the incoming solar radiation
for conservation of body heat. These bears can harness this energy and use only what is
necessary for maximum conservation. The heads of these bears are slimmer than any other
bear for access to seal breathing holes for hunting. The teeth of these bears have also
evolved for the tearing of flesh rather than for mashing of vegetation. These bears have
evolved to the harshest place on this planet, and therefore have no other habitat. Polar
bears are superbly adapted to their surroundings with their white coats as camouflage,
thick layers of insulating blubber, and keen senses of smell, and sight. No other predator
in the Arctic is better equipped to deal with the freezing temperatures than these bears.
Habitat
Polar bears thrive in the Arctic. This is the most
natural terrain for these bears as they are adapted to the ice shelves, and the freezing
waters of the Arctic. These bears will wander off of the ice sheets for two months out of
the year, yet will not stray for long as the Arctic is their home. These bears are adapted
to the freezing temperatures from negative 35 degrees below zero to a mild 20 degrees
above zero (Fahrenheit). See natural history below for more explanations of the natural
habitat that these bears live in.
Natural History
Ecology / Home range
Polar bears have adapted to one of the harshest areas on
the Earth, the Arctic. The ecology of this frozen wasteland is not land, but ice. A giant
frozen ocean that covers five million square miles of tundra, icebergs, and snow.
The polar ice pack is in constant motion in a spiral clockwise motion, but the motion is
interrupted by land masses, tides, currents, and differences in water densities. In some
areas ice may travel as much as 50 miles a day. (Eliot 1998) This constant motion means
that polar bears, which are thought to be nomadic, must compensate for the drift by
traveling steadily in the opposite direction. Ice is the home for polar bears for at least
nine months out of the year, and in the high arctic, much of the year. Pack ice is the
world that polar bears know best, and this is a place where long stretches of open water
called "leads" go to pressure ridges where snow catches in drifts to cover the
breathing holes, and birth lairs of seals. (Davids 1982) Scientists believe that at first
these bears scavenged from seal carcasses that had washed ashore, and gradually began to
hunt the seals by waiting at the water's edge as the seals surfaced to breathe. This is
believed to be an important step in the evolution of the Polar Bear as there was an
untapped ecological niche. (Eliot 1998)
These bears did not always exist in the Arctic, and have evolved from a land
carnivore to a highly skilled and camouflaged hunting machine. From an evolutionary
standpoint, Polar bears are a relatively new species. The first animals that are
recognized as bears go back to the Miocene epoch, some 20 million years ago. (Hugh
1986) Bears were originally spread over all of the continents except Australia, and
Antarctica. Some 200,000 years ago, when the glaciating periods were frequent, and covered
much of Eurasia, and the Arctic Ocean was completely frozen, brown bears began to wander
in search of food. By approximately 125,000 years ago, a new species of bear had appeared
in Eurasia, spilt off from its brown bear ancestors. This new species is said to have
split from the other bears due to competition for food, and most likely being shunted away
by massive glaciers, and extreme weather patterns. (Hugh 1986) This new species of bear
was now classified as Ursus maritimus.
Mating
Polar bears only mate with one another, and will not
mate with any other bear. These bears can copulate in April and May, and then the
fertilized egg is held in the uterus for four or five months until October when the bears
are ready to dig their dens. Most bears den along river-beds, or out on the sea ice. There
are several known den populations (Wrangel Island, Russia, and Northern Alaska), and some
bears will return to the same area year after year to have cubs. (Hugh1986) These
dens are like an igloo, designed to hold heat in. Usually there is a tunnel entryway, and
the birthing quarters are at a higher level to trap the warm air inside. Female bears do
all the digging, with no assistance from the male bears. There are usually two to three
cubs in each litter, and the cubs open their eyes and begin to walk at six weeks old. The
female bears nurse the cubs with milk that is 33 percent richer than any other bear's
milk. (Davids 1982) Only milk from whales and seals are richer in fat content than the
polar bears milk. (Davids 1982) This milk is pure energy for the cubs, and helps to
regulate their body temperature. The mother bear will stay with the cubs until they are at
least one year old.
Adaptations
These bears are equipped with some of nature's
best senses; excellent eyesight, especially for moving objects, and an excellent sense of
smell. Some bears can pick up the scent of a dead animal for over fifty miles
(somewhat similar to the shark smelling blood in the water). (Eliot 1998) Polar bears are
incredibly strong as well. There are some accounts of bears dragging dead whales twice
their size. Polar bears are also excellent runners, and can climb extremely fast. They can
move from 12 to 18 miles an hour and some up to 25 miles an hour on smooth ice pack. These
bears are also excellent swimmers (having evolved to catch marine prey), and use their
front paws (which are webbed), to propel themselves at a maximum of 8 miles an hour in the
water. (Eliot 1998) They can swim nonstop for a hundred miles, and can stay
submerged for two minutes. This is also another way that the bear hunts, diving below it's
prey, and surprising it with an attack from below. Polar bears are incredibly patient
hunters, and have been observed waiting for several hours to catch prey (Davids 1982) .
These bears also have a thick layer of fat, or blubber (similar to whales), that protects
them from the intense cold. The head and snout are longer than any other bear's, and
its teeth are smaller and more jagged: a better design by nature to tear the flesh of it's
food source, seals. The once dark brown coat has turned white, blending in with the arctic
surroundings ( Polar Bears' fur is actually white at the base, and almost clear at the
tips ).
When a Polar Bear attacks, only one word describes it, lightning. These bears are so
quick, that an attack on a surfacing seal only takes a few seconds. Polar Bears are also
unhurried eaters, and chew every bite, only using what it has to. Most bears will eat only
the fat of its prey, gorging on it for pure energy, and saving the energy for warmth.
(Larson 1971) Polar bears are well adapted to the harsh conditions of the arctic, and will
continue to survive as long as humans do not intrude any farther than they already have.
These creatures also have a very strong tie with the social fabric of the
Eskimo, and Inuit peoples. For centuries these bears have been called " nanuk "
by the Inuit, and are highly respected. To Eskimos, the Polar bear is a shaman, a
being of infinite wisdom, and in communication with the spirit world. There are many myths
about the polar bear, and have been passed down from as early as the 12th century. These
myths continue to be told, and will do so as long as this mighty creature is around.
Evolution
The ancestors of polar bears originated in Europe, near
the northern countries that today are known as Scandinavia, Sweden, Greenland, Norway, and
the Soviet Union. (Larson 1971) The earliest classified bears were known as cave bears
(Ursus etruscus), and are also the progenitors of the grizzly bear (Ursus horribilis).
These bears were also classified as brown bears, and in this era, were the sizes of a
small modern dog (Davids 1982).
From an evolutionary standpoint polar bears are relatively new, and as
late as 20 years ago these bears were given a separate genus, (Thalarctos).(Nicklin
1998)Yet, the fact that crosses of European, and American bears have produced fertile
offspring returned the bears to the genus (Ursus). When the last glacial age had frozen
the entire Arctic Ocean, a bridge was created that led to these brown bears wandering from
one existing continent to another. Bears were originally found on all of the continents
except Australia and Antarctica. There have been no fossils of polar bears found that
pre-dates the last glaciation.
The Arctic is where these bears have evolved, and in doing so have changed
the food chain complexity, and their adaptations for tapping a certain niche. The
adaptations that these bears have gone through have enabled them to use land as well as
water to survive. Evolving their physical appearance and body structure over some 200,000
years, these bears have evolved into a formidable hunter that has tapped the food source
of ringed seals living in the Arctic Ocean. Polar bears have evolved especially for
hunting, and storing energy in this harsh climate. Their stomachs have grown larger than
any of their relatives, and can hold up to 150 pounds of food.(Nicklin 1998) This
adaptation is used for storing vital energy in the freezing temperatures. The teeth of
these bears have also changed over time, and have grown sharper and more widely spaced
apart to better tear the flesh of their prey. Most of their relatives have flatter teeth
that are closer together for eating smaller animals, and vegetation.
These adaptations are a major breakthrough in the way that polar bears
hunt, store energy, and survive. Some scientists believe that polar bears are at the very
beginning of evolving into an animal that is as comfortable in the water as it is on land.
(Davids 1982) Others say that this adaptation is a modern evolutionary breakthrough
comparable to that of reptiles taking to flying. (Hugh 1986)
Nearest Relatives
Polar bears are all classified in the order (Carnivora),
in the family (Ursidae), and in the genus (Ursus). Polar bears are related to all other
bears except Koala bears. What differentiates these bears from their counterparts is their
size, and use of energy. Most polar bears are at least on quarter larger than any other
bear. Polar bears are excellent conservationists, and use only what energy is necessary to
survive in the arctic.
The closest relatives to polar bears are the grizzly, and kodiak bears.
These two species of bear share the same approximate shape, senses, and bone structure,
yet have completely different hunting, dinning, and mating patterns. All of these bears
have a very acute sense of smell, excellent eyesight, and powerful muscle structures.
Polar bears also share some of the same hibernation characteristics as their relatives,
yet the techniques are unique in the polar bears' case.
Hibernation of the polar bear is perhaps the most refined response to
starvation of any hibernating, or non-hibernating mammal. The polar bear is considered a
hibernator because it's reactions are similar to those of small hibernating animals that
show a decreased heart rate, metabolic rate, and body temperature. Even so, there are
several reasons that make the hibernation of polar bears unique compared to their
relatives.
Polar bears hibernate at a normal body temperature of 31 to 35 degrees
Celsius. Their dormancy is continuos from 3 to 7 months depending on the sex of the bear.
The bears neither eat, drink, urinate, nor defecate while they are in the den. They are
also easily aroused into a mobile, reactive state, aware of their surroundings, and are
able to defend themselves. In contrast to the relatives of these bears, the hibernation
patterns have changed dramatically along with their evolution. (Davids1982)
Female polar bears also have a unique reproduction process that no
other bear has. This process known as “ delayed implantation “, enables theses
bears to copulate in the spring, and store the fertilized embryo in the uterus until the
bear has stored enough energy to dig a den, and birth the cubs. Most female bears do not
copulate until they are in the 5th or 6th year of life, and even then these bears will
search for the mate of their choosing. (Davids 1982)
How old are they?
The polar bear has an evolutionary history that dates
back from 100,000 to 250,000 years ago in the mid-Pleistocene epoch. (Middleton 1997)
These bears split off from the race of brown bears within the last glacial period, and
have continued to evolve ever since. Polar bears also have a human relationship history,
as they are prized for their dense fur coats. Some of the earliest recorded records of
these bears are found in annals of the European king Harold the fair-haired of Norway in
850A.D. . (Larson 1998) Two polar bears were caught for him as a gift, and in return for
the gift he gave the hunter a ship, a crew, and a trunk full of gold to catch him another
bear. The hunter never returned.
Throughout the middle ages polar bears have been prized as possessions
and Emperor Henry the III of Germany, and Henry the III of England both had polar bears as
mascots at their courts. (Nicklin 1998) Polar bears have been revered for their coats, and
hunting these bears dates back to the ninth century. The Inuit and Eskimo people have
revered these bears in their communities since the evolution of their people.
Additional data
Due to the declining amount of these bears in the
arctic, the U.S. passed the Marine Mammal Act (1976) in which polar bears are protected
from being hunted except by Alaska natives. In 1973, Russia, Canada, Norway, the U.S., and
Greenland signed the International Agreement on Polar Bear Conservation. This was the
first joint compact ever signed for these bears. This agreement states that polar bears
can only be hunted by native people, and there is a limit on the number than can be hunted
as well. Some Eskimo and Inuit people still hunt and kill up to 150 bears a year. Most of
them are used for the blubber, and the fur coats. There are approximately 25,000 to 40,000
polar bears living in the arctic, and are not considered to be endangered.(Nicklin1998)
All of humankind has a stake in the arctic, and for every species of animal that is
hunted, the beauty of the land is diminished. The polar bear will continue to exist, and
evolve if there is sufficient non-interference from the most dangerous predator, humans.
Distribution
Where does the polar bear live, and why?
The five million square miles of tundra, snow, and ice are
arbitrated by the polar bear. No other predator of this vast wasteland of bitter
cold is better adapted to survival and sustainability. The polar bear has been able to
coexist in the wild due to the remote habitat in which it lives. In Alaska, from Point Lay
between Wainwright, and Cape Lisbourne, and West to Russia’s Wrangel Island, and a
Northern group extending to the Canadian border is where polar bears hunt, den, and roam
the icepack. The land of the polar bear is therefore not land, but ice. A giant frozen
ocean, ranking fourth in size after the Pacific, Atlantic, Indian, and five times larger
than the Mediterranean.
There are no polar bears in the Antarctic. Most bears have a strong
attachment to an area, even though they must keep traveling against the Westward direction
of the prevailing ice drift. During spring, before the breakup, they do move East in
search for mates, feeding grounds, and firmer ice. Those on the West coast move North, yet
they generally return to their homeground.(Hugh1986) Once in awhile these bears will roam
far inland near populated areas and will occasionally scrounge in landfill sites, or
investigate people’s homes. Sadly, these wandering bears are usually shot by people
who claim self defense, or by conservation officers who proclaim public safety.(Stirling
et al.) Scientists believe this behavior is much like a
“ walkabout”, that is part of their inherent thinking pattern.
Other species such as lions, moose, and primates have similar behavior.(Davids 1982)
Incredibly far as some bears may roam, none can survive for long away from the ice and the
ocean.
Type of distribution: Continous/Arctic
It has been generally believed that these bears are nomadic,
yet this is not true. Even though these bears do travel in search of food, most bears keep
to the same area in what are called “populations”.(Davids 1982) In the world,
there are at least a dozen discrete populations, yet within these there are smaller
sub-populations of bears. Canada may have as many as ten to twenty sub-populations, which
occasionally intermingle.(Davids 1982) Polar bears range across the Arctic, and some have
been tracked wandering as far as 30,000 kilometers from the area in which they normally
inhabit.(Eliot 1998) Today between 25,000, and 40,000 bears roam this frozen world.
Elevation ranges
The polar bear lives on the ice pack that is contained
in the arctic circle above 60 degrees north latitude. As mentioned before, some bears will
roam as far south as 50 degrees north latitude, and off of the ice shelves. The ranges
that these bears inhabit does not change more than a few hundred feet in elevation on the
tundra. There are glaciers, and snow drifts that these bears will climb up, yet the
changes in actual elevation is relatively small.
Temperature range
The Arctic Circle is home to some of the coldest
temperatures on Earth. There have been records of the air temperature being 100 degrees
below zero. (Fahrenheit) The entire Arctic Circle rarely has air or water temperatures
above the freezing level, and this range lasts throughout 9 months of the year. In the
Spring months, the temperatures will rise to the point in which some of the ice pack will
melt. This is when polar bears tend to wander the most, and search for mates. The Arctic
receives very little precipitation, yet when it does it is usually in the form of snow, or
falling ice. Permafrost covers most of the habitat in which these bears live, and in some
areas, the ground is frozen year round.
Distribution limits
Polar bears tend to keep to the same area, and hunting
grounds. Limits on their distribution is usually attributed to lack of food, melting of
the ice pack, or human intrusion. Polar bears have tapped a specific niche of hunting
their primary food source, seals. When the seals move, so do the bears. These bears are
dependent on this certain food source (although they will eat birds, and small whales),
and will follow the seals until they have found the breeding areas or dens of these seals.
In the Spring, when the ice pack begins to break up, these bears travel to the firmer ice
to avoid floating ice chunks, and to search for mates. Polar bears will also move to avoid
human contact, and most tend to stay away from scientists, or human made creations such as
vehicles, buildings, or boats. The main limit upon the bears' distribution is the
temperature. Polar bears are adapted to the extreme cold, and do not survive well below 50
degrees North latitude (there are bears in zoos, yet rarely do they survive the length
that they would in the wild).
Distribution changes
The ancestors of these bears came from Europe,
from the cave bear,(Ursus etruscus), the progenitor of the Grizzly Bear, (Ursus
horribilis), also known as the Kodiak. No fossils of these bears have been found
that predate the last glaciation. The first animals that are recognized as bears date back
to the Miocene epoch, some 20 million years ago. There were no polar bears at this time.
This evolved species is relatively new, and scientists believe that some 200,000 years ago
when the Arctic ocean was completely frozen over, hungry brown bears wandered in search of
a new food source.(Eliot 1998) These powerful predators started to adapt for both marine,
and land hunting. “ Some scientists say that the adaptation to water represents a
modern evolutionary breakthrough comparable to that of reptiles taking to flying “.
(Davids1982)
Polar bears vary in color from almost pure white to a pale lemon wash, yet there is no
connection between color and location.
Polar Bears thrive in the Arctic, and will continue to do so in this vast
wilderness as long as the seal populations remain stable, and human encroachment does not
interfere with their habitats.
Other interesting issues
Polar bears have a rich history with the
Eskimo, and Inuit peoples. These bears are regarded as shamans and holy beings. There are
infinite stories from these two races of people that place these bears as their
protectors, and neighbors. Polar bears share the same climatic challenges that these two
races of people do, and the Eskimo and Inuit people think of them as gods who share their
same habitat, food source, and temperature challenges.
Bibliography
Encyclopedia Brittanica. 1998. Polar bear. E.B. Publishing, Chicago.
9:187-189
R.C. Davids. 1982. Lords of the Arctic. New York, Macmillan publishing
M.Hugh. 1986. Kingdom of the Ice Bear. London, BBC Publishing.
Stirling, Jinkel, Smith, Cross, Robertson. 1977. The Ecology of
the Polar Bear
Canadian Wildlife Services, Minister of wildlife publishing
Larson,Thor, April 1971. " Polar Bears ".National Geographic Magazine. 139(4):574-590
F. Nicklin, January 1998. " Stalkers of the High Arctic
"
National Geographic Magazine 193(1):53-71
WWW.Discovery.com/polar/bears/html
Author: Wayne Kasworm ( no title)
WWW.Nature-net.com/bears/polar.html
Author: Don Middleton
Title: " The bears den "
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