Behavioral Ecology II

Primate Communication

• Highly complex among primates

• Can be deliberate or autonomic

• Includes:

  • Body language (gestures, posture)

  • Vocalizations (grunts, hoots)

  • Facial expressions

  • Odors

  • Yawns and tooth exposure

Language in Primates

• Communication is different from language

• Humans have a unique system of words, grammar, and speech

• Non-human primates (NHPs) use:

  • Gestures

  • Vocal signals

  • Learned behaviors (e.g., ASL in chimps and gorillas)

Communication and Dominance

• Used to establish social hierarchy

• Dominance gestures:

  • Mounting of lower-ranking males (e.g., baboons)

  • Eye contact (threatening in chimps)

  • Yawning to expose canines (baboons)

  • Flashing eyelids as warnings

• Submission gestures:

  • Crouching

  • Presenting hindquarters

Vocalizations & Displays

• No true language in NHPs

• Specific vocalizations:

  • Alarm calls (up to 30 different calls for different predators)

  • Food alerts

• Displays include:

  • Chest beating (gorillas)

  • Tearing vegetation (chimps)

  • Charging and screaming

Aggressive Behaviors

• Competition for resources (food, mates)

• Often involves threat displays but can escalate to physical fights

• Mating-related aggression:

  • More intense in species with mating seasons

  • Ongoing in species without mating seasons

Affiliative Behaviors

• Strengthen social bonds

• Physical contact-based behaviors:

  • Touching, hand-holding, hugging

  • Allogrooming:

    • Removes dirt and parasites

    • Releases endorphins (reduces pain, promotes well-being)

    • Lowers blood pressure

Altruism in Primates

• Helping others at a cost to oneself

• Examples:

  • Sharing food

  • Adopting orphaned primates

  • Child rearing assistance

• Three hypotheses:

  1. Kin Selection: Favoring relatives to pass on shared genes

  2. Reciprocal Altruism: Helping others expecting a future favor

  3. Group Selection: Benefiting the group leads to individual survival

Reproductive Behaviors

• Estrus: Period of female fertility

  • Includes behavioral & physical changes (e.g., genital swelling)

  • Can lead to temporary pair bonding

• Reproductive strategies:

  • K-selected species (e.g., primates, elephants): Few offspring, high parental care

  • r-selected species (e.g., mice, turtles): Many offspring, little care

Sexual Selection

• Intrasexual selection: Male competition for mates

• Intersexual selection: Female mate choice (e.g., selecting colorful males)

Infanticide

• Males kill infants of ousted dominant males

• Ensures:

  • Females return to estrus sooner

  • New male’s genes are passed on

Primate Culture & Tool Use

• Cultural behavior is learned, often through observation

• Tool use examples:

  • Sticks: Termite fishing, depth testing

  • Leaf sponges: Water collection, cleaning fur

  • Stones: Cracking nuts

  • Sharpened sticks: Used as spears (chimps)

• Species with tool use:

  • Chimps, bonobos, gorillas, orangutans, some monkeys

Conflict & Territoriality

• Groups have home ranges

  • Core areas never overlap

• Intergroup conflict occurs when groups invade territories

• Coalition patrols (usually males) defend borders

• Chimpanzee conflicts:

  • Silent invasions using gestures

  • Isolated males attacked

  • Infants killed from rival groups

Factors Affecting Primate Behavior

• Diet & resource distribution

• Locomotion & body size

• Mating system & reproductive investment

• Kin selection & reciprocal altruism

• Social structures & group dynamics

Summary

Primate behavior is highly complex, shaped by communication, aggression, affiliation, altruism, reproduction, culture, and conflict. Social dynamics are heavily influenced by dominance, reproductive strategies, and environmental factors. Tool use and cultural behaviors highlight learning and adaptation in primates.