Primate Social Systems and Reproductive Strategies

Social Systems of Primates

• Group Size

  • Refers to the number of individuals that typically live together.

  • Can range from solitary individuals to groups of several hundred.

• Group Composition

  • Describes group membership based on age (adult, juvenile, infant) and sex.

  • Varies across species:

  • Some groups consist of a mother and offspring.

  • Others may have one male and one female with their offspring, or one male with multiple females.

• Mating Systems

  • Refers to the pairing of males and females.

  • Common types:

  • Polygyny: One male mates with multiple females.

  • Monogamy: One male mates with one female.

  • These systems may vary even within the same mating type (e.g., solitary vs. group living).

• Ranging Behavior

  • Describes how animals move in their environment.

  • Most primates have a home range for daily activities.

  • Some defend a territory within the home range to protect against conspecifics.

• Dispersal Patterns

  • Describes the movement of individuals to new groups for reproduction.

  • Males typically disperse to reduce competition, while females often remain with relatives (philopatry) to enhance their alliance and food access.

• Social Interactions

  • Encompass how individuals interact, including:

  • Affiliative Behaviors: Friendly interactions like grooming and playing.

  • Agonistic Behaviors: Conflicts over resources like food and mates.

  • Dominance hierarchies may form based on these interactions, dictating access to resources.

Types of Primate Social Systems

• Solitary

  • Individuals do not associate regularly; primarily mothers with offspring.

  • Mating system is usually polygyny with males possessing larger, overlapping ranges with females.

  • Example: West African potto and Bornean orangutans.

• Single-Male, Single-Female

  • Consists of one male, one female, and their young.

  • Group size typically 2-5.

  • Mating system is monogamous, with pair bonds formed through mutual grooming.

  • Example: Bolivian Gray titi monkeys and gibbons.

• Single-Male, Multi-Female

  • One male with multiple female partners.

  • Group size can range from a few to around 50.

  • Mating system is polygyny, often with a dominant male.

  • Competition for mates typically leads to sexual dimorphism.

  • Example: Hanuman langurs and gorillas.

• Multi-Male, Multi-Female

  • Multiple males and females live together.

  • Group size can vary from 10 to 500 individuals.

  • Mating system is polygamous, with dominant hierarchies impacting reproductive success.

  • Example: Vervet monkeys and ring-tailed lemurs.

• Fission-Fusion

  • Groups change size and composition based on resource availability.

  • Members can split (fission) or come together (fusion) dynamically.

  • Exhibits a fluid community structure, generally with polyandrous mating systems.

  • Example: Chimpanzees and spider monkeys.

• Multi-Male, Single-Female

  • Groups consist of multiple males with one breeding female.

  • This system involves competitive breeding dynamics, often resulting in cooperative breeding practices among non-breeders.

  • Example: Marmosets and tamarins.

Reproductive Strategies

• Parental Investment

  • Defined as the time and resources devoted by a parent to ensure their offspring’s success.

  • Females invest significantly more in their offspring due to energy costs of pregnancy and lactation.

• Sexual Selection

  • Refers to traits selected that maximize mating success, divided into:

  • Intrasexual Selection: Competition among males, emphasizing traits such as size and weaponry.

  • Intersexual Selection: Traits that make males more attractive to females; females exhibit choice to maximize offspring health and genetic advantages.

• Evolution of Strategies

  • Female strategies focus on resources for pregnancy and selecting strong males.

  • Males focus on accessing receptive females, improving their chances through displays and competitive traits.