Behavioral Ecology

1. Innate behavior

Innate behaviors are developmentally fixed — they appear in essentially the same form in all members of a species without prior experience. They are strongly influenced by genes and often triggered by a simple cue. A fixed action pattern (FAP) is a sequence of unlearned acts that, once started, runs to completion even if the trigger disappears; the cue that sets it off is the sign stimulus.

Two simple forms of directed movement are also largely innate. A taxis is movement toward or away from a stimulus (a moth flying toward light). A kinesis is a nondirectional change in activity rate in response to a stimulus (a sow bug moving more in dry air, which by chance carries it back toward moisture). Seasonal behaviors such as bird migration rely on innate direction-finding (sun, stars, Earth's magnetic field), often fine-tuned by learning.

2. Learning

Learning is a durable change in behavior that results from experience:

• Habituation — loss of response to a repeated, harmless stimulus (a bird stops fleeing a scarecrow that never moves).
• Imprinting — forming a strong social attachment during an early sensitive period. Hatchling geese follow the first moving object they see, usually a parent. The tendency to imprint is innate; the object imprinted on is learned.
• Classical conditioning — associating an arbitrary stimulus with a consequence (Pavlov's dogs salivating at a bell that predicted food).
• Operant conditioning (trial-and-error learning) — associating a behavior with its consequence; rewarded actions are repeated (a rat pressing a lever for food).
• Cognitive learning — using reasoning, memory, and problem-solving rather than simple association.

3. Social behavior

Social behavior is any interaction between individuals, studied through its effects on fitness. Communication is the transmission of a signal that changes another animal's behavior; signals can be chemical (pheromones), auditory, visual, tactile, or electrical.

Altruism is behavior that lowers the actor's own fitness while raising another's — a puzzle for evolution because it seems to contradict "survival of the fittest." Two explanations resolve it:

• Kin selection favors altruism toward relatives, who share copies of the actor's genes. Selection acts on inclusive fitness — an individual's own offspring plus the offspring of relatives it helps. Hamilton's rule predicts altruism is favored when the benefit to the recipient, multiplied by relatedness, exceeds the cost to the actor (rB > C). This explains a ground squirrel alarm-calling to warn kin at personal risk, and why eusocial insects (bees, ants, termites) have sterile workers that help the queen raise siblings.
• Reciprocal altruism is the exchange of favors between unrelated individuals over time, favored when partners meet repeatedly and cheating is costly.

Mating systems — monogamy, polygyny, and polyandry — are shaped by ecology and the demands of parental care.

How it works

Kin selection explains altruism step by step:

1. Individuals vary in genes that influence behavior, and some genes affect helping.
2. A gene for helping a relative can spread because the relative likely carries copies of that same gene.
3. Hamilton's rule predicts when helping is favored: benefit to the recipient (B) × relatedness (r) must exceed the cost to the actor (C), or rB > C.
4. Siblings share about half their genes (r ≈ 0.5), so saving a sibling can pay off when the helper's cost is lower than half the sibling's reproductive benefit.
5. Over generations, genes promoting help toward kin increase — not because individuals "choose" generosity, but because natural selection acts on the inclusive fitness of those genes.

Common confusions

Memory aids

"Innate is installed, learned is downloaded." Remember that altruism only seems puzzling until you think about inclusive fitness — helping relatives is helping your own genes.

Quick review

Topic Recap

• Behavioral ecology explains both how behavior works (proximate) and why it evolved (ultimate).
• Innate behaviors such as fixed action patterns, taxes, and kinesis require no prior experience.
• Learning ranges from habituation and imprinting to classical conditioning, operant conditioning, and cognitive problem-solving.
• Communication transmits signals; altruism is explained by kin selection (inclusive fitness, Hamilton's rule) and reciprocal altruism.
• Behavior is shaped by natural selection acting on populations and connects directly to fitness, conservation, and health.

Knowledge Check

1. What is the difference between a proximate and an ultimate cause of behavior?
2. Why is imprinting considered partly innate and partly learned?
3. How does Hamilton's rule (rB > C) explain altruism toward relatives?
4. How does reciprocal altruism differ from kin selection?
5. Which type of learning describes a reduced response to a repeated harmless stimulus?

Answers and Rationales

1. Answer: A proximate cause is the immediate mechanism or trigger (how the behavior occurs); an ultimate cause is the evolutionary reason the behavior exists (why it increased fitness). Why: Both are valid scientific questions, but they answer different levels of "why."
2. Answer: The tendency to imprint is innate, but the object imprinted on is learned from experience during a sensitive period. Why: This shows innate and learned behavior can combine in one trait.
3. Answer: Relatives share genes, so helping a relative survive and reproduce can propagate the helper's own genes; selection acts when the benefit to the relative weighted by relatedness exceeds the cost to the helper. Why: This resolves the apparent paradox of self-sacrifice.
4. Answer: Kin selection favors helping relatives who share genes; reciprocal altruism is a conditional exchange of favors between unrelated individuals. Why: Kin selection relies on shared ancestry; reciprocal altruism relies on repeated interaction and returned benefit.
5. Answer: Habituation. Why: Habituation is specifically the loss of response after repeated exposure to a harmless stimulus.