Lions case study Flashcards
What are some of the Social organisation of African lions
Synchronous oestrus
Frequent copulation
Cooperation
Infanticide
Lion prides (Kenya)
3-12 adult females and their cubs.
1-6 adult males.
Females do most of the hunting.
Territory size 20 - 400 km2.
Depends on prey density and pride size.
Lion prides (males)
Males defend the pride and territory.
Larger prides are more successful at defending kills from hyenas.
Larger prides can defend cubs and territory from other male lions.
Female lions
All pride females are closely related.
Females remain in the pride all of their lives.
Females have a long reproduce life.
From age 4 to 18 years.
Females smaller than males.
Weight 120 - 180 kg
Length 2.4 - 2.7 m
Male lions
Males leave natal pride after three years.
Spend several years as nomads before attempting to take over a pride.
After a successful take over they will remain with the pride until driven out by new males.
Reproductive life short. as they need to overtake a pride to then mate with the females.
50-100% larger than female.
Weight 150 – 240 kg; length 2.6 - 3.3 m.
Male size is very important in male–male conflicts.
Large body size is costly.
Need > 7 kg of meat per day.
Longer, darker manes signal aggressiveness and greater fighting ability.
Testosterone.
Synchronous oestrus of pride females.
Lions may breed throughout the year.
Within a pride females show synchronised oestrous
this leads to synchrony of births.
Mechanism is likely to be the influence of an individual’s pheromones on the oestrus cycles of other pride females.
Similar effects known in other social mammals.
What is the function of synchronous oestrus cycles?
Within a pride, litters tend to be born at the same time.
Cubs born synchronously survive better.
Crèches are protective coalitions against infanticidal males.
Groups of females are better able to defend their offspring
Communal suckling releases mothers from parental care, allowing other activities.
Young males more likely to have companions when leaving pride.
Why do female lions cooperate?
Females cooperate in hunting, cub defence and suckling.
The latter is very rare in mammals.
Within a pride female lions are highly related.
Share a high proportion of alleles with each other and the cubs.
Kin selection
What is kin selection
Characters favoured due to beneficial effects on the fitness of close relatives.
evolutionary driver the selection for traits in organisms that are very closely related.
(inclusive fitness)
Frequent copulation
Lioness on heat for 2-4 days every month if not pregnant.
Females copulate every 15 mins.
Copulation induces ovulation.
Birth rate is low and survive to adulthood.
Over 3,000 copulations for each cub that survives to adulthood.
1)Causal explanation – high probability of ovulation failure.
Female lions may need to copulate so frequently to stimulate ovulation.
2)Functional explanation 1 – reduces value of a single copulation to pride males.
Minimises male–male conflict over mating and risk of injury to female.
3) Functional explanation 2 – increases paternity uncertainty.
Any individual pride male could be the father of the cubs.
Advantageous to the female as male lions kill cubs of other males.
Infanticide by male lions
When males take over a pride they often kill the cubs.
Similar effect occurs in mice.
The Bruce Effect= The presence of a strange male induces abortion in pregnant females.
1)Causal explanation – may be the unfamiliar odour.
2) Functional explanation= Cubs were fathered by previous male.
Females with cubs may not be in oestrus for >20 months.
If the cubs are killed this is reduced to 4 - 5 months.
Male reproductive life is short, so infanticidal males are likely to produce more cubs.
Female lions and infanticide
Infanticide benefits males but not females.
Females attempt to defend cubs but males larger and risk of injury is high.
Females have a best-of-a bad-job strategy.
Take over synchronises females and increases sexual activity of females.
Females solicit males and increase competition between male coalitions
Largest male coalition becomes resident.
Large male coalitions remain in pride longer, allowing females to reproduce successfully.
Why do males cooperate?
Kin selection?
Males in coalitions are often related, but this is not always the case.
Reciprocal altruism?= behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism’s fitness, with the expectation that the other organism will act in a similar manner at a later time.
Coalitions are small and stable, providing idea conditions for reciprocity.
Mutualism – Coalition size is very important and all individuals benefit from being in larger group.
