Behavioral Ecology

1. Behavioral Ecology Overview

• Study of the evolution of behavior in response to ecological and environmental factors.

• Behaviors evolve through natural selection.

• Behaviors that enhance survival and reproduction are favored and passed on.

2. Behavior and Genetics

• Behavioral genetics examines the role of genes in shaping behavior.

• In insects and invertebrates, behavior is largely genetically determined.

• In birds and mammals, behavior involves a mix of genetics and learning.

• Primate behavior is influenced by complex social structures.

3. Social Structure in Primates

• Defined by group composition, size, and sex ratio.

• Influenced by natural selection to optimize survival.

• Affects individual interactions and relationships.

Why Live in Groups?

• Competition for resources is highest within a species.

• Group living offers advantages such as:

  • Increased access to food through cooperative defense.

  • More eyes for resource detection.

  • Reduced predation risk.

Factors Influencing Social Structure

• Resource distribution

• Predation risks

• Access to mates

• Body size

• Diet and Basal Metabolic Rate (BMR)

• Dispersal patterns

• Life histories

• Human activities

4. Resource Distribution and Diet

• Different food types impact group size and social behavior:

  • Insects (widely scattered) → favors solitary living.

  • Leaves (abundant and dense) → supports large groups.

  • Fruits and nuts (clumped and dispersed) → supports smaller, flexible groups.

Examples:

• Chimpanzees: Forage in subunits within clumped areas.

• Aye-ayes: Solitary and insectivorous.

• Gorillas: Live in groups in dense forests.

5. Predation and Its Effects

• Primates face threats from birds of prey, big cats, wild dogs, and other primates.

• Larger terrestrial primates have bigger canines for defense.

• Large communities can chase off predators (e.g., lions, cheetahs).

6. Mating and Social Systems

• Different social structures lead to variations in mating access:

  • Solitary (e.g., tarsiers, orangutans).

  • Monogamy (e.g., gibbons, owl monkeys).

  • Polygyny (one male, multiple females; e.g., gorillas).

  • Polyandry (one female, multiple males; e.g., tamarins).

  • Polygamy (multimale-multifemale groups; e.g., chimpanzees).

7. Body Size and Metabolic Rate

• Larger primates have lower BMR and require less energy-dense foods (e.g., leaves).

• Smaller primates have higher BMR and require nutrient-rich foods (e.g., fruits, insects).

8. Dispersal Patterns

• Natal dispersal: One sex leaves its birth group at maturity.

• Male dispersal is more common.

• Female dispersal occurs in some species (e.g., chimpanzees).

• Reduces inbreeding and mate competition.

9. Life History Traits

• Trade-off between fast reproduction vs. longevity.

• Fast life history (e.g., mouse lemurs): Frequent reproduction, early maturity.

• Slow life history (e.g., orangutans): Long lifespan, late maturity.

Sex-Based Offspring Investment

• Some species adjust offspring sex ratio based on environmental factors:

  • High-ranking Rhesus macaques produce more sons.

  • Savanna baboons inherit rank through mothers.

  • Human birth sex ratio changes during stressful events (e.g., 2011 Japan earthquake, 2008 financial crisis).

10. Activity Patterns

• Nocturnal primates → Small groups or solitary.

• Diurnal primates → Larger groups (except orangutans).

11. Human Impact on Primates

• Deforestation for agriculture and ranching disrupts learned behaviors and social structures.

12. Dominance Hierarchies

• Females compete for food (high rank = slight reproductive advantage).

• Males compete for mates (high rank = major reproductive advantage).

• Higher-ranking males mate more frequently at optimal reproductive times.

Summary

• Primate behavior is shaped by natural selection, genetics, and environment.

• Group living offers survival advantages, but competition and hierarchy exist.

• Food availability and predation influence social structures.

• Mating systems vary across species, affecting reproductive success.

• Human activities threaten primate survival by altering habitats and behaviors.