by Matthew Norton
For anyone who has seen the northern or southern elephant seal, Mirounga angustirostris and Mirounga leonine respectively, gather on beaches during the breeding season may have noticed that there are many females accompanied by a single male, or at least a very small group of males, which can outsize the females several times over. This is a classic example of a polygamous mating system, where the male attempt to father as many offspring as possible by dominating a harem of females and excluding the smaller males. Every male wants dominance over this harem, which causes contests between the dominant male and potential challengers. These contests can turn in violent and bloody fights.
The most famous of these contests is the violent and bloody fights which ends in one male ending up dead or seriously injured (https://www.youtube.com/watch?v=bpb7Oks5kWI), but in most cases these disputes over access to females are settled without bloodshed. For the loser it makes no sense to risk death, or serious injury, in a fight they cannot win, especially as they can still force an occasional mating with a female by sneaking around the harem. While preferable to trying to usurp the dominant male, it is still a risky strategy as the resistance from the female, who themselves may be injured or lose pups, may attract the attention of the dominant male. For the winner, even if they could easily crush their opponent, they would be better off saving as much time and energy for future contests.
For both males, deciding how to settle their dispute depends on how clear the difference in size and fighting ability between them is. If one male is clearly smaller he may simply back down and his larger opponent may not even need to assert his dominance. However, if the difference is less conspicuous then each male may need more information about their opponent’s size and fighting ability relative to their own before they can determine if they are the weaker opponent and that they should back down. They do this by making visual threats and roars, which indicates their age and size, at each other, if that fails then a bloody fight to the death, or serious injury, will make it abundantly clear who is the stronger male.
However, avoiding the bloody fights is only a viable option if they still have future mating opportunities available to them. From an evolutionary perspective death is just as bad as living through their last breeding season without fathering any offspring. For any male that is large and strong enough to hold a harem there is a good chance that they are close to the end of their lives and so they cannot afford to back down from an opponent.
From a human perspective
Humanity has had a long, and bloody, history with elephant seals with both northern and southern species being hunted to near extinction for the oil in their blubber. Fortunately since the 20th century sealing activities have become heavily regulated and both species are now protected under various pieces of legislation and their current conservation status is least concern. However, they are still at risk from other human impacts, such as climate change and overfishing of prey species, which have been attributed to some population declines in the southern elephant since the 1950s.
Both elephant seal species are also less well equipped to withstand these impacts as they would have been in pre-sealing years. While their numbers have recovered, they are descended from the few individuals that survived the intense sealing period, with a considerable loss in genetic diversity as a result. Genetic diversity refers to the number of alternative versions, alleles, of each gene in the population, which can generate variations in features, from body weight to body chemistry and behaviour, between individuals.
Natural selection works by altering the abundance of these alleles in the population in response to environmental conditions, with the alleles most suitable for these conditions increasing in abundance. However, under low genetic diversity it is unlikely that a meaningful number of individuals will possess the alleles suitable to respond to a change in environmental conditions.
All around the world we are making great strides in protecting endangered species and helping them come back from the brink of extinction, for example in the last two years the conservation status of the snow leopard and giant panda has been changed from endangered to vulnerable. However, if such species are to recover and thrive in the long term there needs to be a substantial recovery in their genetic diversity, but this can take far longer than a recovery in population size. Therefore extensive protection would be needed for a long time after they are no longer classed as endangered, especially with all the threats that they face because of human activities, such as invasive species, plastic pollution and climate change.
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All other images are public domain and do not require attribution