Ursus (mammal)
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Ursus is a genus in the family Ursidae (bears) that includes the widely distributed brown bear,<ref>Template:Cite web</ref> the polar bear,<ref>Template:Cite web</ref> the American black bear, and the Asian black bear. The name is derived from the Latin ursus, meaning bear.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>
Taxonomy and systematics
Extant species
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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".
Fossils
- †Ursus deningeri Richenau, 1904
- †Ursus dolinensis (Garcia & Arsuaga, 2001)
- †Ursus etruscus Cuvier, 1823
- †Ursus ingressus Rabeder, Hofreiter, Nagel & Withalm 2004
- †Ursus kudarensis Baryshnikov, 1985
- †Ursus minimus (Devèze & Bouillet, 1827)
- †Ursus pyrenaicus (Depéret, 1892)
- †Ursus rossicus Borissiak, 1930
- †Ursus savini (Andrews, 1922)
- †Ursus sackdillingensis Heller, 1955
- †Ursus spelaeus Rosenmüller, 1794
- †Ursus vitabilis? Gidley, 1913
Mating system ecology
The mating systems within the genus Ursus are primarily classified as polygynous, polyandrous and promiscuous.<ref name=":0">Template:Cite journal</ref> Both males and females mate with more than one partner and use various strategies to increase their reproductive success.<ref name=":0" /> Since bears are sexually dimorphic, sexual conflict is a primary driving force behind sexual selection influencing intra-sexual and inter-sexual competition.<ref name=":0" /> Unlike more social species, bears, being solitary mammals, have wide-ranging habitats to locate potential mates.<ref name=":1">Template:Cite journal</ref> 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.<ref name=":2">Template:Cite journal</ref> Intra-sexual selection is then characterized by male-male competitions influenced by female mate choice.<ref name=":0" />
Mating seasons fluctuate based on species dependent on geographical location.<ref name=":2" /><ref name=":3">Template:Cite journal</ref> 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).<ref name=":2" /><ref name=":3" /> 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.<ref name=":0" /> 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.<ref name=":0" /> There is a very loose dominance hierarchy within bear mating systems due to their solitary nature.<ref name=":0" /> 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.<ref name=":0" /> Overall, dominance hierarchies have lower adaptive strategies in solitary species and dominance is established based on encounters during the breeding season.<ref name=":1" />
The mating system is generally characterised by two main components, the search phase and the encounter phase.<ref name=":3" /> During the breeding season, both males and females expand their home ranges to help increase the likelihood of finding potential mates.<ref name=":2" /><ref name=":4">Template:Cite journal</ref> Males, especially, adapt a roaming strategy, covering a large geographic range to find receptive females and tracking them via chemoreceptors.<ref name=":2" /> 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.<ref name=":4" />
Male-male competition
Males compete for females using contest competition, scramble competition and sperm competition as mechanisms for sexual selection.<ref name=":2" /> The pre-copulatory mechanisms, including contest and scramble competition, are conditional mating tactics that are used based on an individual's phenotype.<ref name=":1" /> 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.<ref name=":1" /> Age and size are positively correlated and as males mature, they grow in size and experience, monopolizing receptive females.<ref name=":1" /> 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.<ref name=":2" />
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.<ref name=":1" /><ref name=":4" />
Another male strategy observed by male bears is sexually selected infanticide.<ref name=":3" /> This results in males killing the offspring of other males to directly and indirectly improve their own reproductive success.<ref name=":3" /> 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.<ref name=":0" />
Female mate choice
Female choice is based on the cost of searching for a mate and the quality of a mate.<ref name=":3" /> Since females are induced ovulators, studies suggest that they may have control over the paternity of their offspring.<ref name=":3" /> This may be done through pre- and post-copulatory counter-strategies that involve cryptic female choice and sexually selected infanticide.<ref name=":3" /> The hypothesis of sexually selected infanticide is a female counterstrategy that can directly and indirectly improve their fitness.<ref name=":0" /> 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.<ref name=":0" /><ref name=":1" /><ref name=":4" />
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.<ref name=":0" /><ref name=":1" /> This demonstrates the conditional mating tactics that male bears may consider based on their age and size,<ref name=":1" /> as well as the counter-strategies of females, including sexually selected infanticide and cryptic female choice.<ref name=":0" />