Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 51.3 Selection for Individual Survival and Reproductive Success Can Explain Diverse Behaviors
Animal behaviors—ranging from foraging to mating—evolve through natural selection to maximize individual survival and reproductive success. Behavioral diversity reflects trade-offs, environmental pressures, and sexual selection strategies shaped over time.
1. Foraging Behavior and Natural Selection
- Foraging: includes searching, identifying, and capturing food
- Drosophila larvae show genetic variation:
- Rover allele (forR): long-distance foraging
- Sitter allele (fors): short-distance foraging
- Selection depends on population density: low favors sitter, high favors rover
2. Optimal Foraging Model
- Animals should maximize nutrition and minimize cost (energy, predation)
- Example: Northwestern crows drop whelks from ~5 meters—an optimized behavior
3. Predation Risk Affects Foraging
- Mule deer avoid food-rich forest edges due to mountain lion predation risk
- Behavior reflects trade-off between energy gain and safety
4. Mating Behavior and Reproductive Success
- Includes seeking mates, courtship, competition, and care
- Mating systems:
- Monogamous: long-term pairs, shared care
- Polygamous:
- Polygyny: one male, many females
- Polyandry: one female, many males
- Sexual dimorphism more pronounced in polygamous species
5. Parental Care and Certainty of Paternity
- Birds: high male care when certainty is high → monogamy common
- Mammals: maternal care dominates due to lactation
- Certainty of paternity:
- High in external fertilization → more male care (e.g., fish)
- Low in internal fertilization → less male care
- Some males guard mates or remove rival sperm to increase paternity assurance
6. Sexual Selection and Mate Choice
- Intersexual selection: one sex chooses mates (e.g., songs, displays)
- Intrasexual selection: individuals of same sex compete (e.g., kangaroos)
- Examples:
- Stalk-eyed flies: females prefer longer eyestalks
- Zebra finches: imprinting affects mate preference
- Mate-choice copying: guppies follow others’ preferences
7. Agonistic Behavior and Alternative Strategies
- Agonistic behavior: ritualized contests for access to resources or mates
- Behavioral polymorphism allows multiple strategies to persist
- Example: Side-blotched lizards:
- Orange males: aggressive, control large territories
- Blue males: cooperative, control smaller areas
- Yellow males: sneak copulations by mimicking females
- Game theory: explains coexistence through rock-paper-scissors dynamics
- Frequency-dependent selection maintains diversity by favoring rarer strategies
In a Nutshell
Behaviors evolve through natural selection to enhance survival and reproductive success. Animals balance risk and reward in foraging, display diverse mating systems, and compete or cooperate based on environmental and social cues. Sexual selection and game theory explain why multiple behavioral strategies can persist in populations over time.