Social and mating systems Flashcards
What is the definition of a social unit or social system?
The set of conspecific animals that interact regularly.
Interact more so with each other than with members of other social units.
What are the aspects of social organisation?
Size, sexual composition and spatiotemporal cohesion of a social unit.
Group size
Operational sex ratio
Adult male/ adult female ratio
Is the group made up of cohesive or fission-fusion or solitary individuals organised into ‘neighbourhoods’
What is the definition of a mating unit or mating system?
The individuals that mate within a social unit.
Describes the subset of social interactions
Has a genetic component
- number of matings that result in new members of the social unit
- production of viable offspring
What is the definition for a social structure?
The pattern of social interactions and resulting relationships within the social unit
What diagram can be used to understand social structure?
A socio-gram
Is the social unit often equivalent to the mating unit?
No because not all individuals in a group mate together. There can be extra group copulation where mating takes place outside of pair bonding. But the social unit remains pair bonded.
What is the social organisation, social structure and mating system of a SOLITARY social unit?
Social organisation: solitary but organised into neighbourhoods.
Social structure: Patrilineal, neither sex bonded, but related females often in overlapping ranges
Mating system: Dispersed polygyny ( Females mate with one male but they don’t live together)
What is the social organisation, social structure and mating system of a PAIR-BONDED social unit?
Social organisation: Cohesive groups.
Social structure: Matrilineal, female bonded
Mating system: Polygamous = multi-male, multi-female mating.
Each male invests mainly in one female. But paternity tests suggest extra-group copulation.
E.g Gibbons, Siamangs, some Calitrichids.
What is the social organisation, social structure and mating system of a UNI-FEMALE, MULTI-MALE social unit?
Social organisation: Fission-fusion, multi-level societies
Social structure: Unrelated, non-female bonded, neither sex bonded
Mating system: Polyandrous = Uni-female, multi-male mating. There is either one female in a group or more than one female but only one is reproductively active due to reproductive suppression of subordinates. Benefits of this are marmosets give birth to twins. When relatives are suppressed they are more likely to help look after the young through kin selection.
E.g Tamarins and Marmosets
What is the social organisation, social structure and mating system of a UNI-MALE, MULTI-FEMALE OR MULTI-MALE, MULTI-FEMALE social unit?
Social organisation: Cohesive or OMU’s organised into multi-level societies/
Social structure: Female bonded or neither sex bonded.
Mating system: Polygynous = uni-male, multi-female mating.
Males monopolize access to females. Females mate monogamously.
Intense sexual dimorphism - body size and canine size due to intra-sexual competition over mates.
However these factors change depending on the species. For example;
Mountain gorillas have female dispersal and are non-female bonded. Where as Hanuman Langurs have male dispersal and are female bonded despite the fact both species have the same social system of uni male, multi-female.
In some cases species show BOTH uni-male, multi-female and multi-male, multi-female. This depends on the number of females and their degree of reproductive synchrony.
See this most commonly on the leaf eating langurs in thailand.
With Polygyny mating structures it is very hard to control all the females which leads to reproductive synchrony. This limits the amount of females within a group because one male wouldn’t be able to control all the other males trying to mate with females.
Why when describing a species is it important to understand the point of view when observing a species in a multi-male, multi-female group?
Because this will influence the decision on what social, mating system is present.
For example in gorillas; a multi-male, multi-female group where the dominant male monopolizes all mating.
Social system: multi-male, multi-female
Mating system: uni-male, multi-female (polygynous)
Social structure: non-female bonded because female social relationships are not strong.
What is the definition of a cohesive group?
Stay together all the time but inter - individual distances - proximity to each other (lemurs hudle, howlers sit arms length e.g)
Groups are cohesive but spread out to reduce competition.
What is meant by a fission-fusion group?
This is a fluid structure.
During the day animals feed in “parties” of differing composition or alone. Sub group size changes depending on abundance and quality of food.
Group often comes back together to sleep.
Called “communities” because group structure is not evident at all times.
Fission-fusion is beneficial because of increased predator protection and protection of food.
What species is fission-fusion seen in?
Chimpanzees and spider monkeys.
Some studies showing the blue eyed black eyed lemurs showing evidence of fission-fusion
Often seen in frugivores.
What is meant by a multi-level society use specific species to illustrate your answer?
They vary in complexity.
This is seen in Gelada baboons and snub nosed monkeys but groups seem relatively cohesive.
Groups are composed of one male units (OMUs) and all-male bands all grouped together.
Their diets are ubiquitous.
Lot of tension within groups because of bachelor groups trying to take over from the alpha.
Collaboration is short. Bachelor alliances break down quickly because of the competition for females.
Gelada baboon females have a lot of say over who is alpha. It is their choice to stay with alpha.
