Ursidaebears

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Diversity

Bears are a small group of mostly large mammals, with 8 species in 5 genera (Ursus, Tremarctos, Melursus, Helarctos, and Ailuropoda). Although Ursidae is not diverse, species in this family are widespread and culturally significant to human populations throughout their range. (Flynn, et al., 2005; Nowak, 1991; Vaughan, et al., 2000)

Geographic Range

Bears are found on all continents except Antarctica and Australia, but are primarily found throughout the northern hemisphere, historically occurring as far south as the Atlas Mountains of northwestern Africa, the Andes of South America, and the Sunda shelf region. This range has been reduced in historical times as a result of human persecution and habitat destruction. For example, brown bear (Ursus arctos) populations in the Atlas Mountains are thought to be extinct and their range has been significantly altered in North America and Europe. (Nowak, 1991; Pasitchniak-Arts, 1993; Vaughan, et al., 2000)

Habitat

Bears occur in nearly all terrestrial habitats throughout their range, from Arctic tundra and polar ice floes to tropical and temperate forests, mountains, grasslands, and deserts. Although some bear species occur in arid areas, proximity to water is important. Bears are most abundant and diverse in temperate and boreal regions. Most species are habitat generalists, changing preferred foods, activity patterns, and denning quarters with local conditions. Ailuropoda melanoleuca, however, is found primarily in the montane bamboo forests of southern China. (Chorn and Hoffman, 1978; DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Vaughan, et al., 2000)

Physical Description

Bears are large, robustly built animals. The smallest species, Helarctos malayanus ranges in size from 25 to 65 kg, the largest individuals can weigh up to 800 kg (Ursus maritimus). Males are larger than females, sometimes more than twice their size. Bears have small, rounded ears, small eyes, and very short tails. Most species have long, rough fur, and the hairs that make it up are generally unicolored (rather than being agouti, the common pattern among mammals). Sun bears have a smooth coat. Most bears are brown, black, or white; some have striking white marks on the chest or face. Giant pandas are well-known for their distinctive bands of black and white fur. Bear skulls are massive, with unspecialized incisors, elongate canines, reduced premolars, and bunodont cheek teeth. All bear species possess robust, recurved, non-retractile claws that they use for digging and ripping. The feet of bears are plantigrade, and most have hairy soles, although tree climbing bears, such as Helarctos, have naked soles. There are five digits on each foot. Giant pandas (Ailuropoda melanoleuca) have an additional, opposable feature of the forepaws, sometimes called a panda's "thumb". It is not a true digit but a pad-covered enlargement of the radial sesamoid bone. Pandas use this opposable structure to manipulate bamboo. (Chorn and Hoffman, 1978; DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Vaughan, et al., 2000)

The skulls of bears are elongated. They have an alisphenoid canal, and the paroccipital processes are large and not fused to the bullae, which are not enlarged. Curiously, the lacrimal bone of bears is vestigial. Their cheekteeth are bunodont, and the carnassials are flattened and specialized for crushing, not secodont. The incisors are unspecialized; the canines are long and slightly hooked; and the first three premolars are small and weakly developed if present at all. The dental formula is 3/3, 1/1, 3-4/4, 2/3 = 40-42.

Technical characters (Lawlor, 1979; Nowak, 1991; Vaughan, et al., 2000)

  • Sexual Dimorphism
  • male larger

Reproduction

Male and female bears generally associate only briefly for mating. Males monitor the estrus condition of females in their home range and will remain close for a few days when females are receptive. Multiple mating is practiced by both sexes. (Lariviere, 2001; Nowak, 1991)

Bears give birth to 1 to 4 young, usually 2, at intervals of 1 to 4 years. There is evidence of delayed implantation in all species. Gestation lengths ranging from 95 to 266 days, with implantation being delayed from 45 to 120 days. Actual gestation lengths may be closer to 60 to 70 days. Births in temperate species occur during the winter when the female is dormant. The cubs nurse during the dormant period and the entire metabolic demands of the female must be met by her fat reserves. Births in Helarctos malayanus may occur at any time of the year. Sexual maturity occurs at from to 3 to 6.5 years old, usually occurring later in males. Growth continues after sexual maturity. Males may not reach their adult size until 10-11 years old. Females reach adult sizes usually around 5 years old. (Chorn and Hoffman, 1978; DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Rogers, 1999)

Females give birth to their young in protected areas, often a den of some kind, until they are capable of getting around well, at several months of age. Bears are very small when born, from 90 (Ailuropoda melanoleuca) to 680 (Ursus arctos) grams at birth. They are born with their eyes and ears closed and are either naked or with only a fine layer of fur. Cubs grow rapidly, polar bears go from 600 grams at birth to 10 to 15 kg within 4 months. Weaning occurs from 3.5 (Ursus thibetanus) to 9 (Ailuropoda melanoleuca) months. Young stay with their mother for up to 3 years, but young of most species disperse after 18 to 24 months. Females are very protective of their young and it is likely that cubs learn about obtaining food and shelter during their extended juvenile time with their mother. (Chorn and Hoffman, 1978; DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Nowak, 1991; Pasitchniak-Arts, 1993; Rogers, 1999; Vaughan, et al., 2000)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • extended period of juvenile learning

Lifespan/Longevity

Bears are long-lived if they survive their first few years of life. Most mortality occurs in young cubs or dispersing juveniles as a result of food stress. Pre-weaning cub mortality was estimated at 10-30% in polar bears and sub-adult mortality at between 3 and 16%. In American black bears in Alaska, sub-adult mortality was estimated at 52 to 86%. Estimates of longevity in the wild are as high as 25 years. Captive animals have been known to live to 50 years or more (Ursus arctos). (DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993)

Behavior

Bears are generally solitary, with the exception of mothers with their young. Bears are most often nocturnal or crepuscular, but may be active during the day as well. Polar bears (Ursus maritimus) are primarily diurnal. Bears generally take advantage of shelters, such as caves, hollow logs, and cavities in tree roots, as dens. Helarctos malayanus individuals spend much of their time in trees and build platforms for resting. Bears tend to move relatively slowly, with a shuffling, plantigrade gait, but are capable of running quickly when necessary, standing and walking on the rear two feet, and climbing. Polar bears (Ursus maritimus) are excellent swimmers and sun bears (Helarctos malayanus) are quite arboreal. Most bears move throughout a large range in order to meet their metabolic needs. Polar bear females migrate off of pack ice in late fall to give birth to their young in dens. (DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Rogers, 1999; Vaughan, et al., 2000)

Some temperate bear species undergo extended periods of torpor during winters, retreating to underground burrows or caves to escape from temperature fluctuations. They become lethargic and metabolize fat reserves accumulated during the summer and fall. Some physiologists do not consider this a true state of hibernation, as body temperatures do not drop substantially and bears can be readily roused from this state. Others consider this distinction a semantic one and some researchers have proposed that this is a true hibernation because heart rates drop to almost half the normal rate. Bear species that undergo this form of hibernation often give birth during their winter sleep. (Nowak, 1991; Rogers, 1999; Vaughan, et al., 2000)

Communication and Perception

Vision and hearing in bears is not well-developed, but they have a keen sense of smell and use their sensitive lips to locate and maneuver food. Ursus americanus has color vision and has been demonstrated using vision to distinguish food items at close range. Little is known about communication in bears, but grunts, moans, and roars are known from most species. Cubs may be especially vocal, uttering "woofs" and shrill howls when distressed. "Chuffing" is used as a greeting in Ursus arctos. Chemical cues may be used by males in locating receptive females. Home range boundaries, individual identity, and sexual condition may be advertised, both visually and chemically, by tree-scratching and by urinating and defecating on boundary trails. (DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Rogers, 1999; Vaughan, et al., 2000)

Food Habits

Bears are omnivorous and opportunistic. Specific food types may vary by habitat or season. For example, North American brown bears (Ursus arctos) may rely extensively on fruits and insect larvae throughout the year, or may prey extensively on calves during ungulate breeding seasons and on migrating fish. Most species eat primarily fruits and insect larvae but will include vertebrates when they can, carrion, honey, forbs and grasses, seeds, nuts, tubers, fish, and eggs. Bears use their formidable strength, massive forelimbs, and robust claws to tear apart logs and capture prey. Giant pandas (Ailuropoda melanoleuca) are dietary specialists, eating primarily bamboo stems and shoots, but will also include small vertebrates, insects, and carrion in their diet. Polar bears (Ursus maritimus) are the most carnivorous species, preying mainly on seal species, but including fish, small mammals, birds and their eggs, and will scavenge carcasses of whales, walruses, and seals. (Chorn and Hoffman, 1978; DeMaster and Stirling, 1981; Fitzgerald and Krausman, 2002; Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993; Rogers, 1999; Vaughan, et al., 2000)

Predation

Once bears reach their adult size it is unlikely that they will be subject to predation. Cubs are at risk of predation from conspecific bears, sympatric bear species, and other large predators, such as large cats and canids. Female bears are aggressive in defense of their young. (DeMaster and Stirling, 1981; Lariviere, 2001; Pasitchniak-Arts, 1993)

Ecosystem Roles

All bear species, because of their omnivorous diet and large size, impact the populations of prey animals and plant communities in the ecosystems in which they live. Polar bear populations and brown bear populations that rely on large prey, exert significant pressure on prey populations, including breeding seals and elk. Bear species may help to disperse seeds from the fruits they eat. Arctic foxes (Vulpes lagopus) rely heavily on scavenging polar bear kills. (DeMaster and Stirling, 1981; Lariviere, 2001; Pasitchniak-Arts, 1993; Rogers, 1999)

Bears are infected by a wide variety of endo and ectoparasites, including: protozoans (Eimeria and Toxoplasma), trematodes (Nannophyetus salminicola, Neoricketsia helminthoeca), cestodes (Anacanthotaenia olseni, Mesocestoides krulli, Multiceps serialis, Taenia species, and Diphyllobothrium species), nematodes (Baylisascaris transfuga, B. multipapillata, Uncinaria yukonensis, U. rauschi, Crenosoma, Thelazia californiensis, Dirofilaria ursi, Trichinella spiralis, and Gongylonema pulchrum), lice (Trichodectes pinguis), fleas (Chaetopsylla setosa, C. tuberculaticeps, Pulex irritans, and Arctopsylla species), and ticks (Dermacentor and Ixodes species). Infection by Trichinella spiralis is especially common, affecting up to 60% of Ursus maritimus and U. arctos. (DeMaster and Stirling, 1981; Lariviere, 2001; Pasitchniak-Arts, 1993)

  • Ecosystem Impact
  • disperses seeds
Mutualist Species
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Bears are important members of healthy ecosystems and are sometimes used as indicator species of habitat health and wildness. Bears have also been hunted by humans throughout history for their meat, fat, and fur. Other body parts are used in traditional Chinese pharmacopias, although their usefulness in curing ailments has never been demonstrated. Research on the metabolic pathways black bears use during their winter torpor may help in the development of treatments for kidney failure, gallstones, severe burns, and other illnesses. (Lariviere, 2001; Pasitchniak-Arts, 1993; Rogers, 1999)

  • Positive Impacts
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

Bears are often implicated in predation on livestock, although their impact on livestock populations is most often vastly over-stated. This is particularly true of Tremarctos ornatus, which is persecuted for livestock predation despite its primarily frugivorous lifestyle. Bears regularly attack and kill humans when they feel threatened. Females accompanied by their young may be especially aggresssive and unpredictable. Bear attacks that seem at first to be unprovoked, often prove to be inadvertently provoked when investigated. Bears that live near humans, or have become habituated to humans, cause damage by breaking into homes, food stores, and garbage. Some bear species damage crops, such as manioc and corn. (Lariviere, 2001; Nowak, 1991; Pasitchniak-Arts, 1993)

  • Negative Impacts
  • injures humans
    • bites or stings
  • crop pest

Conservation Status

Bears have been hunted and persecuted throughout human history. Most bear populations continue to face hunting pressure and have become fragmented as a result of human habitat destruction and hunting.

The IUCN ranks Malayan sun bears (Helarctos malayanus) as data deficient, polar bears (Ursus maritimus) as lower risk, Asiatic black bears (Ursus thibetanus), sloth bears (Melursus ursinus), and spectacled bears (Tremarctos ornatus) as vulnerable, and giant pandas (Ailuropoda melanoleuca as endangered.

Several brown bear subspecies are listed as endangered under the United States Endangered Species Act: Mexican grizzly bears, Ursus arctos nelsoni, European brown bears, U. arctos arctos, and Tibetan brown bears or horse bears, U. arctos pruinosus. Baluchistan bears, Ursus thibetanus gedrosianus, are also considered endangered.

The following species are on Appendix I of CITES: Ailuropoda melanoleuca, Helarctos malayanus, Melursus ursinus, Tremarctos ornatus, Ursus thibetanus, and populations of Ursus arctos in Bhutan, China, Mexico and Mongolia. All other populations of U. arctos are included in Appendix II. (Convention on the International Trade in Endangered Species of Wild Flora and Fauna, 2005; IUCN Species Survival Commission, 2004; U.S. Fish and Wildlife Service, 2005)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

The fossil record of bears in North America and Eurasia extends to the earlyl Miocene. It is thought that bears reached Africa in the late Miocene and South America in the early Pleistocene. (McKenna and Bell, 1997)

Contributors

Tanya Dewey (author), Animal Diversity Web, Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

References

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