|From top to bottom: brown bear, American black bear, polar bear, Asian black bear.|
|Genus:|| Ursus |
Ursus is a genus in the family Ursidae (bears) that includes the widely distributed brown bear,the polar bear, the American black bear, and the Asian black bear. The name is derived from the Latin ursus, meaning bear.
|Common name and scientific name||Image||Subspecies||Distribution|
| American black bear |
Ursus americanus (earlier Euarctos americanus)
| Brown bear |
| Polar bear |
Ursus maritimus (earlier Thalarctos maritimus)
| Asian black bear |
Ursus thibetanus (earlier Selenarctos thibetanus)
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.Both males and females mate with more than one partner and use various strategies to increase their reproductive success. Since bears are sexually dimorphic, sexual conflict is a primary driving force behind sexual selection influencing intra-sexual and inter-sexual competition. Unlike more social species bears, being solitary mammals, have wide-ranging habitats to locate potential mates. 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. Intra-sexual selection is then characterized by male-male competitions influenced by female mate choice.
Mating seasons fluctuate based on species dependent on geographical location.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). 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. 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. There is a very loose dominance hierarchy within bear mating systems due to their solitary nature. 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. Overall, dominance hierarchies have lower adaptive strategies in solitary species and dominance is established based on encounters during the breeding season.
The mating system is generally characterised by two main components, the search phase and the encounter phase.During the breeding season, both males and females expand their home ranges to help increase the likelihood of finding potential mates. Males, especially, adapt a roaming strategy, covering a large geographic range to find receptive females and tracking them via chemoreceptors. 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 three-15 females.
Males compete for females using contest competition, scramble competition and sperm competition as mechanisms for sexual selection.The pre-copulatory mechanisms, including contest and scramble competition, are conditional mating tactics that are used based on an individual's phenotype. 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. Age and size are positively correlated and as males age, they grow in size and experience, monopolizing receptive females. 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.
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.
Another male strategy observed by male bears is sexually selected infanticide.This results in males killing the offspring of other males to directly and indirectly improve their own reproductive success. 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.
Female choice is based on the cost of searching for a mate and the quality of a mate.Since females are induced ovulators, studies suggest that they may have control over the paternity of their offspring. This may be done through pre- and post-copulatory counter-strategies that involve cryptic female choice and sexually selected infanticide. The hypothesis of sexually selected infanticide is a female counterstrategy that can directly and indirectly improve their fitness. 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.
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.This demonstrates the conditional mating tactics that male bears may consider based on their age and size, as well as the counter-strategies of females, including sexually selected infanticide and cryptic female choice.
The brown bear is a large bear species found across Eurasia and North America. In North America, the populations of brown bears are called grizzly bears. It is one of the largest living terrestrial members of the order Carnivora, 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's range includes parts of Russia, Central Asia, China, Canada, the United States, Hokkaido, Scandinavia, the Balkans, the Picos de Europa and the Carpathian region, especially Romania, Bulgaria, Iran, Anatolia and the Caucasus. The brown bear is recognized as a national and state animal in several European countries.
The polar bear is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear species, as well as the largest extant predatory carnivore. A boar weighs around 350–700 kg (772–1,543 lb), while a sow is about half that size. Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice and open water, and for hunting seals, which make up most of its diet. Although most polar bears are born on land, they spend most of their time on the sea ice. Their scientific name means "maritime bear" and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present. Because of their dependence on the sea ice, polar bears are classified as marine mammals.
Pica is the genus of seven species of birds in the family Corvidae in both the New World and the Old.
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.
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 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. Note all of the confirmed hybrids listed here have been in captivity, but suspected hybrids have been found in the wild.
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.
Cervus is a genus of deer that primarily are native to Eurasia, although one species occurs in northern Africa and another in North America. In addition to the species presently placed in this genus, it has included a whole range of other species now commonly placed in other genera, but some of these should perhaps be returned to Cervus. Additionally, the species-level taxonomy is in a state of flux.
Sexual cannibalism is when a female cannibalizes her mate prior to, or after copulation. It is a trait observed in many arachnid orders and several insect orders. Several hypotheses to explain this seemingly paradoxical behavior have been proposed. The adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis are among the proposed hypotheses to explain how sexual cannibalism evolved. 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 killing of young offspring by a mature animal of the same species, and 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.
Monogyny is a specialised mating system in which a male can only mate with one female throughout his lifetime but the female may mate with more than one male. In this system the males generally provide no paternal care. In many spider species that are monogynous, the males have two copulatory organs, which allows them to mate a maximum of twice throughout their lifetime. As is commonly seen in honeybees, ants and certain spider species, a male may put all his energy into a single copulation, knowing that this will lower his overall fitness. During copulation monogynous males have adapted to cause self genital damage or even death to increase their chances of paternity.
Female copulatory vocalizations, also called female copulation calls or coital vocalizations, are produced by female primates, including human females, and female non-primates. 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 swellings are enlarged areas of genital and perineal skin occurring in some female primates that vary in size over the course of the menstrual cycle. Thought to be an honest signal of fertility, male primates are attracted to these swellings; preferring, and competing for, females with the largest swellings.
Monogamous pairing refers to a general relationship between an adult male and an adult female for the purpose of sexual reproduction. It is particularly common in birds, but there are examples of this occurrence in reptiles, invertebrates, fish, amphibians, and mammals.
Sexual selection in mammals 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 selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females known to make their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females.
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 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.
Extended female sexuality is where the female of a species mates despite being infertile. In most species, the female only engages in copulation when she is fertile. However, extended sexuality has been documented in old world primates, pair bonded birds and some insects. Extended sexuality is most prominent in human females who exhibit no change in copulation rate across the ovarian cycle.
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.