Brown Bear Offspring
The gestational period for brown bears is 6 to 8 weeks, and the females generally give birth to between one and four cubs. The mother cares for the cubs for up to 2.5 years, during which time she will not mate. The males do not contribute to the rearing of offspring.
Why Do Male Brown Bears commit SSI?
Infanticide among animals: A review, classification, and examination of the implications for the reproductive strategies of females gives a suggestion of the potential motivations behind SSI.
Sources of increased fitness from infanticide include:
(1) exploitation of the infant as a resource,
(2) elimination of a competitor for resources,
(3) increased maternal survival or lifetime reproductive success for either mother or father by elimination of an ill-timed, handicapped, or supernumerary infant, and, finally,
(4) increased access for individuals of one sex for reproductive investment by the other sex at the expense of same-sex competitors.
There are however situations where there is no benefit derived from SSI, this can be classified at pathological. In general it is considered that male brown bears commit SSI in an effort to promote their own bloodline.
Female Strategies To Avoid SSI
The cost to the female brown bear is very high. Carrying and rearing cubs takes a toll on her fitness and the loss is significant when the young are killed by males, simply to impregnate her again. As mentioned above females are beginning to develop counter-strategies to avoid SSI whenever possible.
Once such strategy that has been observed in females in an effort to reduce the risk of SSI is multi-male partnering. This multiple mating, or ‘promiscuity’, is considered an attempt to confuse paternity, thereby protecting the cubs from males who think that may have fathered them.
Another tactic is that the females seem to choose to mate with the geographically closest males, which have the highest potential to kill their future cubs. ~ The dilemma of female mate selection in the brown bear, a species with sexually selected infanticide.
Spatio-temporal avoidance is another common, yet high risk strategy, where the females choose to live an elusive lifestyle, staying away from optimal bear resources in order to protect their offspring. Steyaert’s study aimed to see whether this strategy incurred a significant cost in terms of fitness, with the female and her cubs receiving a poor diet as a result of the avoidance of high risk areas.
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