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Predation and Population Interactions: Dynamics, Strategies, and Defenses

Explore the complex relationships between predators and prey, including the Lotka-Volterra equations, functional and numerical responses, predator choices, and prey defenses. Learn about coevolution, predator defenses, foraging strategies, and the effects of herbivore grazing on plants. Discover how predator-prey relationships can influence entire ecosystems.

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Predation and Population Interactions: Dynamics, Strategies, and Defenses

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  1. Chapter 15 Predation

  2. I. Terminology • Predation = one organism is food for another • Carnivory = feeding on animal tissue • Parasitoidism = killing of host by larvae • Parasitism = feeds on host w/out killing • Herbivory = feeding on plants w/out killing • Cannibalism = predator and prey same species

  3. II. Lotka-Volterra dN/dt = rN -CNpreyNprey • Mathematic equations predicting effects of predation on population growth • Population growth for prey • Maximum rate of increase • Removal by predation • Predator population equation • Efficiency of converting kills • Death rate of predators/absence of prey

  4. Relationship between predator and prey • Increase in prey increase in predators • Decrease in prey  predator decrease

  5. III. Predator response • Functional response—prey population increases  predator eats more • 3 types of functional responses • Numerical response—prey population increases  predator population increases Mutual regulation of populations

  6. IV. Predator choices • May choose alternative prey • Turn to more abundant prey type = prey switching • Predator spends less time with less abundant prey • Species may increase as a result • Predator may switch back to original prey—preferences

  7. V. Numerical response • Direct response – predators increase as prey increases • No response – predator population remains same • Inverse response – predator population cannot keep up with prey density

  8. VI. Prey defenses Bumbl;e Bee • Chemical defenses— • Poisonous skin • Odors • Toxins • Camouflage—differ between female/male • Mimicry • Batesianmimicry • Mullerianmimicry Robber Fly Monarch Viceroy

  9. Coevolution between Predator and Prey • Exerting selective pressure on prey • To maintain the population, successful avoidance • Moving in place to stay where they are

  10. Predator Defenses • Physical defenses—armor coats / hard shells / modified hairs • Behavioral defenses—alarms not species specific • Distraction—misdirecting attention • Group living • Reproduction timing

  11. VII. Predation • Ambush—lying in wait • Frogs, alligators, lizards, insects • Low success / little energy • Stalking—deliberate / quick attack • Herons, small cats • Search requires time / pursuit minimal • Pursuit—known location of prey • Large cats, hawks, wolves • Pursuit time great / minimal search Crypiticcoloration blends into environment Alligator mississipiensis Blue Heron, Ergetta caerulea Red-tailed Hawk, Buteo jamaicensis Northern Cardinal, Cardinalis cardinalis

  12. VIII. Cannibalism • Form of intraspecific predation • Found in stressed populations Conditions: • Crowded / dense populations • Stress – low ranked attacked by dominant ones • Presence of vulnerable individuals • May decrease numbers of intraspecific competitorsdecreases chances of extinction or can doom population

  13. IX. 3 way interaction • B eats A • C and D eat B • D eats C • Intraguildpredation = one species eating another sharing same prey (potential competitor) • Resource manager manipulation

  14. X. Foraging strategy • Optimal foraging strategy – provides maximum energy gain • Robins— • Concentrate on most productive • Remain until profitability falls • Leave patch when reaches average level • Ignore low productivity patches American Robin, Turdus migratorius

  15. XI. Herbivore grazing • Biomass consumed = 6-10% of total • Effects may be detrimental / may stimulate new growth • Results indirect or direct • Plants differ in quality of food • Tough, woody, hard to digest • Plant defenses—chemical defenses

  16. XII. Plant defenses • Quantitative inhibitors—long-lived woody plants • More expensive to plant • Reduce digestibility • Qualitativeinhibitors—toxins • Interfere with metabolism • Low cost to plant • Structuraldefenses—interfere with herbivory • Least costly defense

  17. XIII. Predator-prey relationships • Not separate entities • One level influences interactions at other levels • Vegetation, snowshoe hare and lynx • Food shortage for harescauses malnutrition • Increased predation causes decline of hares • Food shortage for lynx

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