Biology 112: Behavior and Ecology

What is Behavior?

  • Definition: Behavior is a response to a stimulus.

  • Behavioral Ecology: Subset of organismal ecology studying behavioral adaptations to ecological selection pressures.

Do Plants Show Behavior?

  • Yes, plants show behavior. Examples include:

    • Phototropism: Growing toward light.

    • Insectivorous Plants:

    • Example: Venus Flytrap

      • Mechanism: Responds to insect touch via tiny hairs, leading to electrical signals.

      • Molecular events cause the pads to close, and enzymes then digest the prey.

Variability in Behavior

  • Fixed, Stereotyped vs. Variability in Behavioral Traits:

    • Innate Behavior:

    • Low variation.

    • Little environmental influence.

    • Adaptive without training (e.g., a lion yawns).

    • Learned Behavior:

    • High variation.

    • Highly influenced by environment.

    • Adaptive because flexible (e.g., chimpanzee using a stem to sponge water).

Behavior Trade-offs

  • Optimal Foraging Hypothesis: Organisms maximize usable energy intake by weighing the costs of finding food against the risks.

Choosing a Mate: Mating Systems

  • Types of Mating Systems:

    • Monogamy: One female mates with one male (e.g., bald eagles, mute swans).

    • Polygamy:

    • Polygyny: One male mates with multiple females (e.g., red deer, horses).

    • Polyandry: One female mates with multiple males (rare, e.g., sandpipers).

    • Promiscuity: Males and females have multiple sexual partners (e.g., honeybees).

  • Example: Emperor penguins exhibit a monogamous system during breeding seasons.

Choosing Where to Go

  • Migration: Long-distance movement associated with seasonal changes.

    • Navigation Methods:

    1. Piloting: Using familiar landmarks.

    2. Compass Orientation: Moving in a specific direction.

    3. True Navigation: Locating a specific place on Earth.

Communication

  • Different types of signals (sound, scent, visual) correlate with habitat.

  • Honeybee Communication:

    • Waggle Dance: Describes the distance and direction of food sources using movement relative to the position of the Sun.

Honest vs. Deceitful Communication

  • Natural selection can favor deceitful communication, observed in species like cuttlefish.

Cooperation: Altruism

  • Definition: Altruism is behavior with a fitness cost to the individual and a benefit to the recipient.

  • Hamilton's Rule: Model assessing how altruistic alleles may increase in frequency. Expressed as Br > C where:

    • B = fitness benefit to beneficiary

    • r = coefficient of relatedness

    • C = fitness cost to altruist.

Conditions of Altruism

  • Altruism is likely when:

    1. Fitness benefits are high for the recipient (high B).

    2. Altruist and recipient are close relatives (high r).

    3. Fitness costs are low for the altruist (low C).

Inclusive Fitness

  • Definition: Combination of direct fitness (own offspring) and indirect fitness (helping relatives).

  • Kin Selection: Natural selection acting through benefits to relatives.

Testing Hamilton's Rule: Prairie Dog Alarm Calls

  • Hypothesis: Alarm calls increase in presence of relatives.

  • Experimental Setup: Monitor alarm behavior in coteries with varying kin relationships.

  • Results: Alarm calls correlated with presence of kin.

Eusociality

  • Definition: Sacrifice of direct reproduction to help a queen’s offspring (found in bees, wasps, and ants).

  • Workers within these colonies have a high coefficient of relatedness (0.75), promoting the rearing of sisters over their own offspring, supporting Hamilton's rule.