Primates_3

Introduction

• Course: ANHB 1101 Human Biology I - Primates 3: Primate Behavioural Ecology

• Instructor: Associate Professor Cyril C. Grueter

• Contact: cyril.grueter@uwa.edu.au

Learning Outcomes

• Understand how social and ecological environments influence primate social organization.

• Explain the relationships between primate morphology and behaviors, including social behavior and mating systems.

Evolution of Primate Traits

• Natural selection promotes behaviors that enhance survival and reproductive success.

• Key factors include:

  • Moving speed

  • Energetic efficiency

  • Mating strategies

  • Maternal care responsibilities

Behavioural Ecology

• Behavioural Ecology studies behavior from an evolutionary and ecological perspective.

  • Behavior results from natural selection leading to adaptations to specific habitats.

  • Anatomical traits affect behavior, e.g., male-male competition relates to sexual dimorphism.

Socioecology

• Socioecology explains social system variations in relation to ecological and biological factors.

  • Resource availability influences:

    • Competition

    • Group dynamics

    • Social interactions

    • Mating patterns

  • Social behaviors are adaptations to environmental contexts.

Social Systems

• Components of social systems include:

  • Social organization: Group composition and cohesion

  • Social structure: Interactions and relationships within groups

  • Mating system: Patterns of mating and genetic consequences.

Survival and Fitness

• Key survival strategies include:

  • Finding food

  • Coordination with mates

  • Raising offspring

  • Avoiding diseases and predators

Costs and Benefits of Group Living

• Costs:

  • Increased competition for resources

  • Higher disease transmission

  • Greater risk of predation

• Benefits:

  • Defense against competitors

  • Reduced predation risk through group vigilance.

Benefits of Sociality: Lower Risk of Predation

• Detection: More individuals spotting predators.

• Deterrence: Group mobbing or chasing off predators.

• Dilution effect: Higher group size reduces individual predation likelihood.

Optimal Group Size

• Group size reflects a balance of sociality costs and benefits, influenced by ecological and social conditions.

Gender Competition

• Females: Compete for food resources.

• Males: Compete for access to females.

Reproductive Success Limitations

• Females: Limited by resource access for offspring.

• Males: Limited by access to females.

• Ecological pressures shape female distribution, affecting male strategies.

Food Requirements

• Essential for survival, growth, and reproduction.

• Dietary specializations lead to anatomical adaptations (e.g., body size, dental characteristics).

• Food distribution varies across habitats, affecting primate adaptations.

Diet Correlation with Body Size

• Insectivores are typically smaller than frugivores; frugivores are smaller than folivores.

• Size differences correlate with energy requirements implications.

Digestion Adaptations

• Primates lack cellulose digestion; reliance on microorganisms (e.g., Colobines have specialized stomachs for this).

  • Colobines: Multi-chambered stomachs for folivory.

  • Cercopithecines: One-chambered stomachs for frugivory.

Diet and Brain Size

• Ecological Intelligence Hypothesis: Frugivorous primates have larger brains to remember food sources and locations (Barton 1996).

Resource Distribution Patterns

• Resource types vary in distribution:

  • Clumped: High-quality foods like fruits.

  • Evenly dispersed: Low-quality foods like leaves.

  • Different distributions affect social structure.

Resource Defensibility

• Clumped resources are often territorial; evenly distributed resources can be contested.

Competition Types

• Scramble competition: First-come, first-served for evenly distributed food.

• Contest competition: Direct competition over defensible food sources.

Feeding Competition in Mountain Gorillas

• Higher feeding aggression observed around fruit than herbaceous food due to resource competition.

Fission-Fusion Dynamics

• Group size and structure adapt based on food availability, resulting in flexible group sizes.

Socioecology Principles

• Distribution of resources impacts competitive dynamics among females, including mating trends and social hierarchies.

Dispersal Patterns

• Primates exhibit varied dispersal patterns based on species:

  • Male dispersal is prevalent in many; female or bisexual dispersal in others.

Reasons for Animal Dispersal

• To avoid inbreeding (natal dispersal).

• Seek better resources or avoid competition.

Primate Social Organization

• Categories of mating systems:

  • Solitary, monogamous, polyandrous, and polygynous.

  • Examines diversity in group formations and reproductive strategies.

Monogamous Relationships

• Males may pair permanently with females if they are dispersed (e.g., Titi monkeys, Gibbons).

Polyandry

• Involves multiple males with one female (seen in Callitrichids).

Polygyny: One-Male Systems

• One male can monopolize a group of females when they are clumped (e.g., Gorillas, Colobus monkeys).

Male Infanticide

• A significant cause of infant mortality, especially after changes in male dominance.

Polygyny: Multimale Systems

• Found in species like chimpanzees and macaques, where multiple males mate with a group of females.

Human Mating Systems

• Majority of human societies operate under monogamous unions, though polygyny is permitted based on subsistence.

Anatomical Evidence of Sexual Dimorphism

• Correlation exists between sexual dimorphism patterns and mating systems across mammals.

Sexual Dimorphism and Humans

• Humans display slight sexual dimorphism, but lesser than ancestral species.

Testis Size and Mating Systems

• Promiscuous species exhibit larger testes compared to monogamous or polygynous species; humans display mild promiscuity.

Conclusion

• Understanding primate behavior and social systems illuminates evolutionary adaptations and ecological interactions.