Ursus | |
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From top to bottom: brown bear, American black bear, polar bear, Asian black bear | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Family: | Ursidae |
Subfamily: | Ursinae |
Tribe: | Ursini |
Genus: | Ursus Linnaeus, 1758 [1] [2] |
Type species | |
Ursus arctos Linnaeus, 1758 | |
Species | |
Synonyms | |
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Ursus is a genus in the family Ursidae (bears) that includes the widely distributed brown bear, [3] the polar bear, [4] the American black bear, and the Asian black bear. The name is derived from the Latin ursus, meaning bear. [5] [6]
Common name | Scientific name and subspecies | Range | Size and ecology | IUCN status and estimated population |
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American black bear | Ursus americanus Pallas, 1780 16 subspecies
| American Southwest and Mexico![]() | Size: Habitat: Diet: | LC |
Brown bear | Ursus arctos Linnaeus, 1758 15 subspecies
| Russia, Central Asia, China, Canada, the United States (mostly Alaska), Scandinavia, and the Carpathian region (especially Romania), Anatolia, and Caucasus![]() | Size: Habitat: Diet: | LC |
Polar bear | Ursus maritimus Phipps, 1774 2 subspecies
| Arctic Circle and adjacent land masses as far south as Newfoundland. | Size: Habitat: Diet: | VU |
Asian black bear | Ursus thibetanus G. Cuvier, 1823 7 subspecies
| Indian subcontinent, Korea, northeastern China, the Russian Far East, the Honshū and Shikoku islands of Japan, and Taiwan![]() | Size: Habitat: Diet: | VU |
A hybrid between grizzly bears and polar bears has also been recorded. Known commonly as a pizzly, prizzly, or grolar bear, the official name is simply "grizzly–polar bear hybrid".
The mating systems within the genus Ursus are primarily classified as polygynous, polyandrous and promiscuous. [10] Both males and females mate with more than one partner and use various strategies to increase their reproductive success. [10] Since bears are sexually dimorphic, sexual conflict is a primary driving force behind sexual selection influencing intra-sexual and inter-sexual competition. [10] Unlike more social species bears, being solitary mammals, have wide-ranging habitats to locate potential mates. [11] Due to the asynchrony of oestrous phases and lengthy parental care by females, bear populations are usually male-biased, meaning that females are more choosy and males are more competitive. [12] Intra-sexual selection is then characterized by male-male competitions influenced by female mate choice. [10]
Mating seasons fluctuate based on species dependent on geographical location. [12] [13] American black bears (Ursus amercanus), brown bears (Ursus arctos) and polar bears (Ursus maritimus) all have mating seasons occurring within a three-month duration during the spring and summer months (approximately May – July), with delayed implantation occurring in late fall (November), and cubs born within the den during early winter (January). [12] [13] Females, on average, mate with three to four males during a mating season and mating males have more variation, mating with one to eight females during a mating season. [10] Since reproductive success is positively correlated with age and size in bear populations, there are also males that do not mate at all until they are able to compete with larger males. [10] There is a very loose dominance hierarchy within bear mating systems due to their solitary nature. [10] Majority of dominance hierarchies are found at food congregations in which population density is high and individuals are ranked based on size, mass, aggressiveness and willingness to fight. [10] Overall, dominance hierarchies have lower adaptive strategies in solitary species and dominance is established based on encounters during the breeding season. [11]
The mating system is generally characterised by two main components, the search phase and the encounter phase. [13] During the breeding season, both males and females expand their home ranges to help increase the likelihood of finding potential mates. [12] [14] Males, especially, adapt a roaming strategy, covering a large geographic range to find receptive females and tracking them via chemoreceptors. [12] Male bears are not considered to be territorial, but they do have large home ranges that may overlap with female home ranges, giving them access to a range of 3–15 females. [14]
Males compete for females using contest competition, scramble competition and sperm competition as mechanisms for sexual selection. [12] The pre-copulatory mechanisms, including contest and scramble competition, are conditional mating tactics that are used based on an individual's phenotype. [11] Males that are larger in size compete more in physical contests to access potential mates, while males that are smaller or medium-sized use scramble competition as a strategy by increasing their ranges to encounter potential mates. [11] Age and size are positively correlated and as males mature, they grow in size and experience, monopolizing receptive females. [11] Observations of broken canines, cuts, wounds and scars demonstrate the costs associated with contests and the importance of physical intra-sexual conflict within polygamous mating systems. [12]
There is also post-copulatory male-male competition that has been documented in species within the genus Ursus. The presence of dual paternity within a litter implies that sperm competition may take place after copulation. [11] [14]
Another male strategy observed by male bears is sexually selected infanticide. [13] This results in males killing the offspring of other males to directly and indirectly improve their own reproductive success. [13] This can directly influence their success by mating with the female when she re-enters oestrus or indirectly by lowering intra-sexual competition with other males and resources. [10]
Female choice is based on the cost of searching for a mate and the quality of a mate. [13] Since females are induced ovulators, studies suggest that they may have control over the paternity of their offspring. [13] This may be done through pre- and post-copulatory counter-strategies that involve cryptic female choice and sexually selected infanticide. [13] The hypothesis of sexually selected infanticide is a female counterstrategy that can directly and indirectly improve their fitness. [10] This is done by selecting for infanticidal males to enforce mate and offspring recognition and indirectly by mating with multiple males in order to have multiple paternity. [10] [11] [14]
Within Ursus, there may be a high variation within the mating strategies observed by both females and males, demonstrating overall plasticity depending on external factors. [10] [11] This demonstrates the conditional mating tactics that male bears may consider based on their age and size, [11] as well as the counter-strategies of females, including sexually selected infanticide and cryptic female choice. [10]
The brown bear is a large bear native to Eurasia and North America. Of the land carnivorans, it is rivaled in size only by its closest relative, the polar bear, which is much less variable in size and slightly bigger on average. The brown bear is a sexually dimorphic species, as adult males are larger and more compactly built than females. The fur ranges in color from cream to reddish to dark brown. It has evolved large hump muscles, unique among bears, and paws up to 21 cm (8.3 in) wide and 36 cm (14 in) long, to effectively dig through dirt. Its teeth are similar to those of other bears and reflect its dietary plasticity.
Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of gamete production is lower for males than it is for females. The different mating tactics employed by males and females are thought to be the outcome of stochastic reproductive conflicts both ecologically and socially.
Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.
A harem is an animal group consisting of one or two males, a number of females, and their offspring. The dominant male drives off other males and maintains the unity of the group. If present, the second male is subservient to the dominant male. As juvenile males grow, they leave the group and roam as solitary individuals or join bachelor herds. Females in the group may be inter-related. The dominant male mates with the females as they become sexually active and drives off competitors, until he is displaced by another male. In some species, incoming males that achieve dominant status may commit infanticide.
An ursid hybrid is an animal with parents from two different species or subspecies of the bear family (Ursidae). Species and subspecies of bear known to have produced offspring with another bear species or subspecies include American black bears, grizzly bears, and polar bears, all of which are members of the genus Ursus. Bears not included in Ursus, such as the giant panda, are expected to be unable to produce hybrids with other bears. The giant panda bear belongs to the genus Ailuropoda.
A grizzly–polar-bear-hybrid is a rare ursid hybrid that has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid in nature was confirmed by testing the DNA of a unique-looking bear who had been shot near Sachs Harbour, Northwest Territories, on Banks Island in the Canadian Arctic. The number of confirmed hybrids has since risen to eight, all of them descending from the same female polar bear.
Monogamous pairing in animals refers to the natural history of mating systems in which species pair bond to raise offspring. This is associated, usually implicitly, with sexual monogamy.
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.
Stegodyphus lineatus is the only European species of the spider genus Stegodyphus. Male S. lineatus can grow up to 12 mm long while females can grow up to 15 mm. The colour can range from whitish to almost black. In most individuals the opisthosoma is whitish with two broad black longitudinal stripes. Males and females look similar, but the male is generally richer in contrast and has a bulbous forehead. The species name refers to the black lines on the back of these spiders. S. lineatus is found in the southern Mediterranean region of Europe and as far east as Tajikistan.
Sexual cannibalism is when an animal, usually the female, cannibalizes its mate prior to, during, or after copulation. This trait is observed in many arachnid orders, several insect and crustacean clades, gastropods, and some snake species. Several hypotheses to explain this seemingly paradoxical behavior have been proposed, including the adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.
In animals, infanticide involves the intentional killing of young offspring by a mature animal of the same species. Animal infanticide is studied in zoology, specifically in the field of ethology. Ovicide is the analogous destruction of eggs. The practice has been observed in many species throughout the animal kingdom, especially primates but including microscopic rotifers, insects, fish, amphibians, birds and mammals. Infanticide can be practiced by both males and females.
Female copulatory vocalizations, also called female copulation calls or coital vocalizations, are produced by female primates, including human females, and female non-primates. They are not purposeful, but instead are evolutionary and are spontaneously produced by female primates, including women, to encourage her partner to produce good-quality sperm during the mating process. Copulatory vocalizations usually occur during copulation and are hence related to sexual activity. Vocalizations that occur before intercourse, for the purpose of attracting mates, are known as mating calls.
Sexual selection in birds concerns how birds have evolved a variety of mating behaviors, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and color differences are energetically costly attributes that signal competitive breeding situations. Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signaling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behavior are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviors.
Sexual selection in mammals is a process the study of which started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, consisting of male–male competition and mate choice that mold the development of future phenotypes in a population for a given species.
Sexual coercion among animals is the use of violence, threats, harassment, and other tactics to help them forcefully copulate. Such behavior has been compared to sexual assault, including rape, among humans.
In behavioral ecology, polyandry is a class of mating system where one female mates with several males in a breeding season. Polyandry is often compared to the polygyny system based on the cost and benefits incurred by members of each sex. Polygyny is where one male mates with several females in a breeding season . A common example of polyandrous mating can be found in the field cricket of the invertebrate order Orthoptera. Polyandrous behavior is also prominent in many other insect species, including the red flour beetle, the adzuki bean weevil, and the species of spider Stegodyphus lineatus. Polyandry also occurs in some primates such as marmosets, mammal groups, the marsupial genus' Antechinus and bandicoots, around 1% of all bird species, such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish.
Sperm competition is a form of post-copulatory sexual selection whereby male sperm simultaneously physically compete to fertilize a single ovum. Sperm competition occurs between sperm from two or more rival males when they make an attempt to fertilize a female within a sufficiently short period of time. This results primarily as a consequence of polyandrous mating systems, or due to extra-pair copulations of females, which increases the chance of cuckoldry, in which the male mate raises a child that is not genetically related to him. Sperm competition among males has resulted in numerous physiological and psychological adaptations, including the relative size of testes, the size of the sperm midpiece, prudent sperm allocation, and behaviors relating to sexual coercion, however this is not without consequences: the production of large amounts of sperm is costly and therefore, researchers have predicted that males will produce larger amounts of semen when there is a perceived or known increase in sperm competition risk.
Infanticide in non-human primates occurs when an individual kills its own or another individual's dependent young. Five hypotheses have been proposed to explain infanticide in non-human primates: exploitation, resource competition, parental manipulation, sexual selection, and social pathology.
Primate sociality is an area of primatology that aims to study the interactions between three main elements of a primate social network: the social organisation, the social structure and the mating system. The intersection of these three structures describe the socially complex behaviours and relationships occurring among adult males and females of a particular species. Cohesion and stability of groups are maintained through a confluence of factors, including: kinship, willingness to cooperate, frequency of agonistic behaviour, or varying intensities of dominance structures.
Formerly or currently considered subspecies or populations of brown bears have been listed as follows: