| Grizzly bears | |
|---|---|
 | |
| Grizzly bear | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Family: | Ursidae |
| Genus: | Ursus |
| Species: | U. arctos ssp. |
| Binomial name | |
| Ursus arctos (Linnaeus, 1758) | |
| |
 | |
| Historic and present range | |
The grizzly bear (Ursus arctos ssp.) is a large subspecies of brown bear inhabiting North America. Scientists generally do not use the name grizzly bear but call it the North American brown bear.
...
Meaning of "grizzly"
Meriwether Lewis and William Clark first described it as grisley, which could be interpreted as either "grizzly" (i.e., "grizzled"—that is, with golden and grey tips of the hair) or "grisly" ("fear-inspiring", now usually "gruesome"). The modern spelling supposes the former meaning; even so, naturalist George Ord formally classified it in 1815 as U. horribilis, not for its hair, but for its character.
...
Ursus arctos - the brown bear
Brown bears originated in Eurasia and traveled to North America approximately 50,000 years ago, spreading into the contiguous United States about 13,000 years ago. In the 19th century, the grizzly was classified as 86 distinct species. However, by 1928 only seven grizzlies remained and by 1953 only one species remained globally. However, modern genetic testing reveals the grizzly to be a subspecies of the brown bear (Ursus arctos). Rausch found that North America has but one species of grizzly. Therefore, everywhere it is the "brown bear"; in North America, it is the "grizzly", but these are all the same species, Ursus arctos.
...
Most adult female grizzlies weigh 130–180 kg (290–400 lb), while adult males weigh on average 180–360 kg (400–790 lb). Average total length in this subspecies is 198 cm (6.50 ft), with an average shoulder height of 102 cm (3.35 ft) and hindfoot length of 28 cm (11 in). Newborn bears may weigh less than 500 grams (1.1 lb). In the Yukon River area, mature female grizzlies can weigh as little as 100 kg (220 lb). One study found that the average weight for an inland male grizzly was around 272 kilograms (600 lb) and the average weight for a coastal male was around 408 kilograms (900 lb). For a female, these average weights would be 136 kilograms (300 lb) inland and 227 kilograms (500 lb) coastal, respectively. On the other hand, an occasional huge male grizzly has been recorded which greatly exceeds ordinary size, with weights reported up to 680 kg (1,500 lb).A large coastal male of this size may stand up to 3 metres (9.8 ft) tall on its hind legs and be up to 1.5 metres (4.9 ft) at the shoulder.
Although variable in color from blond to nearly black, grizzly bear fur is typically brown with darker legs and commonly white or blond tipped fur on the flank and back. A pronounced hump appears on their shoulders; the hump is a good way to distinguish a grizzly bear from a black bear, as black bears do not have this hump. Aside from the distinguishing hump a grizzly bear can be identified by a "dished in" profile of their face with short, rounded ears, whereas a black bear has a straight face profile and longer ears.A grizzly bear can also be identified by its rump, which is lower than its shoulders, while a black bear's rump is higher. A grizzly bear's front claws measure about 2-4 inches in length and a black bear's measure about 1-2 inches in length.
...
Longevity
The grizzly bear is, by nature, a long-living animal. The average lifespan for a male is estimated at 22 years, with that of a female being slightly longer at 26. Females live longer than males due to their less dangerous life; avoiding the seasonal breeding fights in which males engage. The oldest wild inland grizzly was 34 years old in Alaska; the oldest coastal bear was 39,but most grizzlies die in their first few years of life from predation or hunting. Captive grizzlies have lived as long as 44 years.
Hibernation
Grizzly bears hibernate for 5–7 months each year except where the climate is warm, as the California grizzly did not hibernate. During this time, female grizzly bears give birth to their offspring, who then consume milk from their mother and gain strength for the remainder of the hibernation period.To prepare for hibernation, grizzlies must prepare a den, and consume an immense amount of food as they do not eat during hibernation. Grizzly bears do not defecate or urinate throughout the entire hibernation period. The male grizzly bear's hibernation ends in early to mid-March, while females emerge in April or early May.
In preparation for winter, bears can gain approximately 180 kg (400 lb), during a period of hyperphagia, before going into hibernation.[42] The bear often waits for a substantial snowstorm before it enters its den: such behavior lessens the chances predators will find the den. The dens are typically at elevations above 1,800 m (5,900 ft) on north-facing slopes. There is some debate amongst professionals as to whether grizzly bears technically hibernate: much of this debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears can "partially" recycle their body wastes during this period. Although inland or Rocky Mountain grizzlies spend nearly half of their life in dens, coastal grizzlies with better access to food sources spend less time in dens. In some areas where food is very plentiful year round, grizzly bears skip hibernation altogether.
Reproduction
Except for females with cubs,grizzlies are normally solitary, active animals, but in coastal areas, grizzlies gather around streams, lakes, rivers, and ponds during the salmon spawn. Every other year, females (sows) produce one to four young (usually two) that are small and weigh only about 450 grams (1 lb) at birth. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.
Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America. This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old. Once mated with a male in the summer, the female delays embryo implantation until hibernation, during which miscarriage can occur if the female does not receive the proper nutrients and caloric intake. On average, females produce two cubs in a litter and the mother cares for the cubs for up to two years, during which the mother will not mate.
Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions. Male grizzly bears have large territories, up to 4,000 km2 (1,500 sq mi), making finding a female scent difficult in such low population densities. Population fragmentation of grizzlies may destabilize the population from inbreeding depression. The gestation period for grizzly bears is approximately 180–250 days.
Litter size is between one and four cubs, averaging twins or triplets. Cubs are always born in the mother's winter den while she is in hibernation. Female grizzlies are fiercely protective of their cubs, being able to fend off predators as large as male bears bigger than they are in defense of the cubs. Cubs feed entirely on their mother's milk until summer comes, after which they still drink milk but begin to eat solid foods. Cubs gain weight rapidly during their time with the mother — their weight will have ballooned from 4.5 to 45 kg (10 to 99 lb) in the two years spent with the mother. Mothers may see their cubs in later years but both avoid each other.
...
Ecological role
The grizzly bear has several relationships with its ecosystem. One such relationship is a mutualistic relationship with fleshy-fruit bearing plants. After the grizzly consumes the fruit, the seeds are excreted and thereby dispersed in a germinable condition. Some studies have shown germination success is indeed increased as a result of seeds being deposited along with nutrients in feces. This makes grizzly bears important seed distributors in their habitats.
While foraging for tree roots, plant bulbs, or ground squirrels, bears stir up the soil. This process not only helps grizzlies access their food, but also increases species richness in alpine ecosystems. An area that contains both bear digs and undisturbed land has greater plant diversity than an area that contains just undisturbed land. Along with increasing species richness, soil disturbance causes nitrogen to be dug up from lower soil layers, and makes nitrogen more readily available in the environment. An area that has been dug by the grizzly bear has significantly more nitrogen than an undisturbed area.[98]
Nitrogen cycling is not only facilitated by grizzlies digging for food, it is also accomplished via their habit of carrying salmon carcasses into surrounding forests. It has been found that spruce tree (Picea glauca) foliage within 500 m (1,600 ft) of the stream where the salmon have been obtained contains nitrogen originating from salmon on which the bears preyed. These nitrogen influxes to the forest are directly related to the presence of grizzly bears and salmon.
Grizzlies directly regulate prey populations and also help prevent overgrazing in forests by controlling the populations of other species in the food chain. An experiment in Grand Teton National Park in Wyoming in the United States showed removal of wolves and grizzly bears caused populations of their herbivorous prey to increase.This, in turn, changed the structure and density of plants in the area, which decreased the population sizes of migratory birds. This provides evidence grizzly bears represent a keystone predator, having a major influence on the entire ecosystem they inhabit.
When grizzly bears fish for salmon along the coasts of Alaska and British Columbia, they often only eat the skin, brain and roe of the fish. In doing so, they provide a food source for gulls, ravens, and foxes, all of which eat salmon as well; this benefits both the bear and the smaller predators ...
No comments:
Post a Comment