Animal Behavior

Core Review

Innate vs Learned Behavior

Innate behaviors are genetically hardwired — they appear in complete form the first time they are performed, even without prior experience. They are stereotyped (performed the same way each time), species-specific, and independent of environmental variation during development. Key examples:

• Fixed action patterns (FAPs): A sequence of unlearned acts directly linked to a specific stimulus (the sign stimulus or releaser). Once initiated, FAPs are usually carried to completion. Classic example: a greylag goose retrieving an egg that has rolled out of the nest — if the egg is removed mid-retrieval, the goose still completes the head-tucking motion. The stimulus triggers an irreversible motor program.
• Reflexes: Simple, rapid, automatic responses to stimuli (e.g., knee-jerk reflex, withdrawal reflex).
• Taxis: Directed movement toward or away from a stimulus. Phototaxis = movement toward light; chemotaxis = movement toward a chemical gradient.
• Kinesis: Undirected change in activity rate in response to stimulus intensity (e.g., sowbugs moving more rapidly in dry areas, increasing the chance they find a moist spot — but not moving directly toward it).

Learned behaviors are modified by experience. They require interaction with the environment and are often more flexible than innate behaviors:

• Imprinting: A rapid, irreversible learning process occurring during a specific critical period (or sensitive period) early in life. Konrad Lorenz famously demonstrated that newly hatched greylag goslings would imprint on the first moving object they encountered — in his case, Lorenz himself. Imprinting combines innate and learned elements: the drive to imprint is innate; the object of imprinting is learned. Imprinting has long-term consequences for social and sexual behavior.
• Classical conditioning (Pavlovian): An animal learns to associate a neutral stimulus with a biologically significant stimulus. Ivan Pavlov: dogs salivated (unconditioned response) to food (unconditioned stimulus). By ringing a bell (neutral stimulus) before presenting food, the dogs learned to salivate to the bell alone (conditioned response). The key: association of two stimuli.
• Operant conditioning (Skinnerian): An animal learns to associate its own behavior with a consequence. B.F. Skinner: rats in a "Skinner box" learned to press a lever to receive food (positive reinforcement) or to avoid a shock (negative reinforcement). Reinforcement increases behavior frequency; punishment decreases it. Positive reinforcement (adding a reward) is the most effective training method.
• Habituation: A decrease in response to a repeated, harmless stimulus. An animal learns not to respond. Example: prairie dogs eventually stop alarm-calling at non-threatening foot traffic. This is the simplest form of learning, saving energy by ignoring irrelevant stimuli.
• Spatial learning: The use of landmarks and cognitive maps to navigate an environment (e.g., digger wasps using landmark patterns to locate their nests).

Social Behavior and Altruism

One of the great puzzles in evolution: why would an organism reduce its own fitness to help others? Kin selection resolves this paradox. William Hamilton proposed that altruistic behavior toward relatives can evolve because relatives share alleles by common descent. Helping a relative reproduce passes shared alleles to the next generation, increasing the altruist's inclusive fitness (direct fitness + indirect fitness from relatives).

Hamilton's rule: An altruistic allele spreads when rB > C, where:

• r = coefficient of relatedness (probability two individuals share an allele by descent: 0.5 for parent-offspring and full siblings; 0.25 for half-siblings, grandparents; 0.125 for first cousins)
• B = benefit to the recipient (additional offspring produced)
• C = cost to the altruist (offspring lost by helping)

Example: A ground squirrel alarm-calling to warn siblings of a predator. The caller risks its own life (cost C), but if it saves two full siblings (r = 0.5 each, benefit B = 2 × 0.5 = 1.0), and the risk of death is moderate, the altruistic allele can be favored.

Reciprocal altruism occurs between unrelated individuals when the favor is expected to be returned in the future. This requires repeated interactions, the ability to recognize individuals, and memory of past interactions. Example: vampire bats regurgitate blood meals to roost-mates who have failed to feed, and those recipients later reciprocate.

Foraging Behavior

Optimal foraging theory predicts that natural selection favors foraging strategies that maximize energy gained per unit time (or per unit energy expended). Animals face tradeoffs: a predator may prefer larger, more energy-rich prey, but if search time becomes excessive, it may switch to smaller, more abundant prey. Foraging decisions also involve predation risk — an animal may accept lower-quality food in safer locations rather than risk predation for higher-quality food. The marginal value theorem predicts how long a forager should stay in a patch of resources before moving on: depart when the rate of energy gain in the current patch drops below the average rate for the habitat.

Communication

Animals communicate via multiple modalities, each with distinct tradeoffs:

Common Traps

• Confusing classical conditioning (Pavlov — two stimuli associated) with operant conditioning (Skinner — behavior associated with consequence). The DAT will describe a scenario and ask you to identify the learning type.
• Thinking imprinting is purely innate. It has an innate drive but the target is learned during a critical period.
• Habituation ≠ sensory adaptation. Sensory adaptation is a physiological change at the receptor level; habituation is a central nervous system process — the animal learns not to respond.
• Forgetting that kin selection requires the ability to discriminate relatives from non-relatives (kin recognition); otherwise, altruism could be exploited.