Behavioral Ecology Notes

BEHAVIORAL ECOLOGY - ALTRUISM

  • Definition of Altruism

    • An act is altruistic if it reduces the actor's fitness (cost, CC) while increasing the recipient's fitness (benefit, BB).

  • Hamilton's Rule & Inclusive Fitness

    • Inclusive fitness = direct fitness (your own reproduction) + indirect fitness (reproduction of relatives, weighted by relatedness rr).
    • Hamilton's Rule: r \times B > C,
      • where:
        • rr: coefficient of relatedness
        • BB: benefit to the recipient
        • CC: cost to the actor

  • Kin Selection

    • Genes promoting altruism spread when directed toward relatives.
    • Example: Ground squirrels give alarm calls to warn kin of predators.

  • Eusocial Insects: Extreme Altruism

    • Sterile worker castes care for queen's offspring.
    • Haplodiploidy (ants, bees, wasps) sisters share r=0.75r = 0.75.
    • Raising sisters can yield higher indirect fitness than having own offspring.

  • Reciprocal Altruism

    • Helping non-kin with expectation of returned favor.
    • Conditions (Trivers 1971): repeated interactions, recognition & memory, B > C, punishment of cheaters.
    • Example: Vampire bats share blood meals with roost-mates.

  • Alternative Frameworks

    • Multilevel selection: interplay of individual- and group-level benefits.
    • Groups of cooperators may outcompete selfish groups under certain conditions.

  • Medical-Biology Connections

    • Apoptosis: programmed cell death eliminates damaged cells (actor cost) for organism's health (benefit).
    • Microbial Public Goods: bacteria release enzymes that benefit colony; cheater dynamics influence infection & resistance.

  • Key Takeaways

    • Altruism can evolve via kin selection (r \times B > C) or reciprocity.
    • Relatedness and repeated interactions are crucial.
    • Principles apply across taxa-from squirrels to cells.

BEHAVIORAL ECOLOGY - LIVING IN GROUPS

  • What Is Group Living?

    • Definition: Repeated, close-proximity association among conspecifics with coordinated or emergent behaviors.
    • Ubiquity: Occurs in all major animal taxa—from planktonic swarms to primate troops to eusocial insects.

  • Benefits of Group Living

    • Predator Defense
      • Many-Eyes Effect: Shared vigilance lowers individual scanning effort.
      • Dilution Effect: Per-individual predation risk decreases as group size increases.
    • Cooperative Foraging & Information Sharing
      • Local Enhancement: Observing foragers leads naïve individuals to resources.
      • Division of Labor: Specialists (e.g., scouts vs. harvesters) increase efficiency in social insects.
    • Thermoregulation
      • Huddling conserves heat; e.g., emperor penguins rotate positions in dense clusters.
    • Reproductive & Kin-Selection Advantages
      • More mating opportunities in aggregations.
      • Helping close relatives enhances inclusive fitness.

  • Costs of Group Living

    • Resource Competition: More individuals compete for limited food, space, or mates.
    • Disease Transmission: Close contact facilitates parasites and pathogens.
    • Increased Detectability: Large groups can be more conspicuous to predators.
    • Social Conflict: Hierarchies and aggression can stress lower-ranked members.

  • Types of Group Structures

    • Aggregations
      • Characteristics: Temporary, loose-often in response to external stimuli
      • Example: Fish schooling when threatened
    • Colonies
      • Characteristics: Site-attached, long-term
      • Example: Seabird rookeries; bat caves
    • Eusocial Societies
      • Characteristics: Sterile worker castes; reproductive division
      • Example: Ant, bee, termite colonies
    • Fission-Fusion
      • Characteristics: Fluid membership; split and rejoin
      • Example: Chimpanzee communities; some deer

  • Key Theoretical Models

    • Selfish Herd Theory (Hamilton, 1971): Individuals move toward group center to minimize personal predation risk.
    • Ideal Free Distribution: Animals distribute among resource patches to equalize individual gain.
    • Game Theory: Payoff matrices predict when cooperation or defection (group joining or leaving) maximizes fitness.

  • Case Studies

    • Meerkats (Suricata suricatta)
      • Sentinel system: Individuals take turns watching for predators while others forage.
      • Cooperative care: Helpers feed and guard pups, boosting group survival.
    • Honey-Bee Colonies (Apis mellifera)
      • Waggle dance communicates direction and distance of flower patches.
      • Caste system: Workers, drones, and queens specialize in tasks.
    • Mixed-Species Flocks (Neotropical Birds)
      • Species with different foraging niches flock together.
      • Collective vigilance yields lower individual predation risk.

  • Balancing Costs & Benefits

    • Adjustable Group Size: Individuals join or leave groups based on predation risk and resource availability.
    • Behavioral Synchrony: Coordinated movement and signals maintain cohesion (e.g., flock turns).
    • Social Immunity: Collective grooming or antimicrobial secretions reduce disease spread in eusocial insects.

  • Implications Beyond Ecology

    • Human Sociality & Epidemiology: Insights into crowd behavior, disease outbreaks, and public-health strategies.
    • Conservation & Management: Understanding grouping can inform species reintroduction, habitat design, and wildlife corridors.

  • Key Take-Home Messages

    • Group living evolves when its net benefits (anti-predator, foraging, thermoregulation, kin selection) exceed net costs (competition, disease, detectability, conflict).
    • A spectrum of group structures exists-each shaped by ecological pressures and life-history trade-offs.
    • Theoretical models (Selfish Herd, Ideal Free, Game Theory) help predict when and how animals should form, maintain, or leave groups.

BEHAVIORAL ECOLOGY - RESOURCE ASSESSMENT

  • Why Resource Assessment Matters

    • Animals have limited time, energy, and safety. To survive and reproduce they must decide:
      • Resource Value (RV) - How valuable is this item right now?
      • Resource-Holding Potential (RHP) - How likely am I to win or defend it?
    • Accurate answers reduce wasted effort and injury.

  • Key Definitions

    • Resource Value (RV)
      • Plain-English Meaning: Immediate fitness payoff of winning the item
      • Typical Measurement or Example: Fat in a seed; number of eggs a nest can support
    • Resource-Holding Potential (RHP)
      • Plain-English Meaning: Fighting ability relative to rivals
      • Typical Measurement or Example: Body size in beetles; antler span in deer
    • Signal
      • Plain-English Meaning: Trait or action that conveys information about RV or RHP
      • Typical Measurement or Example: Roars, plumage colour, chemical scent
    • Evolutionarily Stable Strategy (ESS)
      • Plain-English Meaning: Strategy (or mix) that cannot be invaded by an alternative once common in the population
      • Typical Measurement or Example: Hawk-Dove mix when injury cost > resource value

  • Contest Assessment Strategies

    • Self-Assessment - Individual quits when its own energy or risk threshold is reached.
      • Example: Salmon stop fighting when aerobic reserves are depleted.
    • Mutual (Sequential) Assessment - Rivals exchange increasingly risky signals, quitting if clearly outmatched.
      • Example: Red-deer stags often settle contests by roaring alone.
    • Cumulative Assessment - Loser quits when total costs inflicted by the opponent exceed its limit.
      • Example: Field crickets accumulate scrape damage until one retreats.
    • Reality: Species may blend strategies depending on context.

  • Classic Theoretical Models

    • Hawk-Dove Game (Maynard Smith)
      • Core Idea: Individuals choose to fight (Hawk) or display (Dove).
      • Key Prediction: When injury cost CC > resource value VV, a mixed ESS emerges.
      • Real-World Evidence: Speckled-wood butterflies: more Hawks over high-sunlight spots.
    • War of Attrition (Parker & Thompson)
      • Core Idea: Contestants avoid dangerous combat and "out-wait" each other with costly displays.
      • Key Prediction: Contest length is highly variable; longer if resource value is high.
      • Real-World Evidence: Fiddler-crab waving bouts vary widely in duration.
    • Sequential Assessment Model (Enquist & Leimar)
      • Core Idea: Rivals sample RHP step-by-step, escalating risk only when necessary.
      • Key Prediction: Contest duration increases sharply as RHP difference shrinks.
      • Real-World Evidence: Cichlid fish mouth-wrestling lasts longest in size-matched pairs.
    • Cumulative Assessment
      • Core Idea: Quit when cumulative costs received reach a personal threshold.
      • Key Prediction: Losers show higher immediate injury or energy debt than winners.
      • Real-World Evidence: Loser crickets have greater scrape damage after pushing bouts.

  • Signals: Keeping Information Honest

    • Costly to fake: Deep croaks require large bodies; small toads cannot mimic.
    • Social policing: Paper wasps attack rivals with "cheater" facial patterns.
    • Handicap principle: Honest signals persist because they impose real costs on high-quality senders.

  • Beyond Fighting

    • Foraging
      • Assessment Rule: Marginal Value Theorem - leave a patch when current intake < average elsewhere
      • Example: Bumblebees track nectar refill rates
    • Territory
      • Assessment Rule: Ideal Free Distribution - individuals distribute so none improves payoff by moving
      • Example: Ducks among feeding ponds
    • Mate Choice
      • Assessment Rule: Sample and assess potential partners; often apply "best-so-far" rule
      • Example: Female birds ranking male song complexity

  • Take-Home Points

    • Define your terms - always translate acronyms back to real-world meanings.
    • Assessment saves resources - wrong decisions waste energy or cause injury.
    • Models guide hypotheses - each predicts specific, testable patterns.
    • Same logic, diverse settings-feeding, mating, territoriality all rely on cost-benefit assessment.