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.
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.
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.
conspecific and sympatric bears
large cats (Felidae)
social canids (Canidae), such as wolves (Canis lupus)
Ursidae preys on: Vulpes vulpes Odocoileus virginianus Puma concolor
This list may not be complete but is based on published studies.
Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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.
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).
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.
Mating System: polygynandrous (promiscuous)
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.
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.
Barcode of Life Data Systems (BOLD) Stats Specimen Records: 389 Specimens with Sequences: 499 Specimens with Barcodes: 300 Species: 12 Species With Barcodes: 11 Public Records: 244 Public Species: 11 Public BINs: 10