Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 51.1 Discrete Sensory Inputs Can Stimulate Both Simple and Complex Behaviors
Animal behavior is shaped by both immediate environmental stimuli and evolutionary history. Behaviors range from simple, instinctive responses to complex patterns of communication, all controlled by the nervous system and shaped through natural selection.
1. Defining Behavior and Tinbergen’s Questions
- Behavior: an action controlled by the nervous system (e.g., vocalizing, scent marking)
- Supports survival, reproduction, and homeostasis
- Tinbergen’s four questions:
- What triggers the behavior?
- How does development influence response?
- How does it promote survival and reproduction?
- What is its evolutionary history?
- Proximate causation: mechanisms and development; Ultimate causation: evolutionary purpose
2. Fixed Action Patterns
- Fixed action pattern (FAP): unlearned, unchangeable behavior sequence triggered by a sign stimulus
- Example: male sticklebacks attack red-bellied intruders, even models
- FAP runs to completion once triggered
- Also seen in moths avoiding bats using evasive flight
3. Migration and Environmental Cues
- Migration: long-distance travel guided by environmental cues (e.g., sun, stars, Earth’s magnetic field)
- Requires navigation through unfamiliar terrain
- Circadian clocks help animals orient to the sun
- Homing pigeons use magnetic fields when visual cues are absent
4. Biological Rhythms
- Circadian rhythms: internal ~24-hour activity cycles
- Circannual rhythms: yearly cycles (e.g., migration, reproduction)
- Controlled by environmental light/dark cues
- Examples: fiddler crab courtship synced with lunar cycles and tides
5. Animal Communication
- Signal: a stimulus from one animal causing a response in another
- Communication: transfer of signals through visual, chemical, tactile, or auditory means
- Example: fruit fly courtship uses all signal types in a stimulus-response chain:
- Visual (orientation)
- Chemical (pheromones)
- Tactile (foreleg tapping)
- Auditory (song)
6. Pheromones and Chemical Communication
- Pheromones: chemical signals important in reproduction and social behavior
- Examples:
- Fruit fly mating behavior
- Silkworm moths detect mates over long distances
- Honeybee queen pheromones regulate hive behavior
- Minnows release alarm pheromones when injured
7. Symbolic Language in Bees
- Waggle dance: communicates food direction and distance
- Angle of dance = direction relative to sun
- Duration and waggles = distance
- Nearby food → bees use round dance
- Scents and landmarks help finalize targeting
In a Nutshell
Animal behaviors are influenced by both genetic programming and environmental stimuli. From fixed action patterns and migratory cues to complex social communication via pheromones and symbolic dance, these behaviors have evolved to maximize survival and reproductive success. Tinbergen’s framework helps uncover both how and why animals behave the way they do.