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Chapter 15
Predation
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
II. Lotka-Volterra
• 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
Relationship between predator and prey
• Increase in prey increase in predators
• Decrease in prey predator decrease
III. Predator response
1. Functional response—prey population increases predator eats more
– 3 types of functional responses
2. Numerical response—prey population increases predator population increases
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
V. Numerical response
1. Direct response – predators increase as prey increases
2. No response – predator population remains same
3. Inverse response – predator population cannot keep up with prey density
VI. Prey defenses
• Chemical defenses—• Poisonous skin• Odors• Toxins
• Camouflage—differ between female/male – Mimicry
• Batesian mimicry• Mullerian mimicry
Robber Fly
Bumbl;e Bee
Viceroy
Monarch
Coevolution between Predator
and Prey•
•Exerting selective pressure on prey
•To maintain the population, successful
avoidance•Moving in place to stay
where they are
• Physical defenses—armor coats / hard shells / modified hairs
• Behavioral defenses—alarms not species specific
• Distraction—misdirecting attention
• Group living
• Reproduction timing
Predator Defenses
VII. Predation 1. Ambush—lying in wait
• Frogs, alligators, lizards, insects• Low success / little energy
2. Stalking—deliberate / quick attack• Herons, small cats• Search requires time / pursuit minimal
3. Pursuit—known location of prey• Large cats, hawks, wolves• Pursuit time great / minimal search
Crypitic coloration blends into environment
Blue Heron, Ergetta caerulea
Red-tailed Hawk, Buteo jamaicensis
Northern Cardinal, Cardinalis cardinalis
Alligator mississipiensis
VIII. Cannibalism
• Form of intraspecific predation– Found in stressed populations
Conditions:
1. Crowded / dense populations2. Stress – low ranked attacked by dominant
ones3. Presence of vulnerable individuals• May decrease numbers of intraspecific
competitorsdecreases chances of extinction or can doom population
IX. 3 way interaction
• B eats A
• C and D eat B
• D eats C
• Intraguild predation = one species eating another sharing same prey (potential competitor)
• Resource manager manipulation
X. Foraging strategy
• Optimal foraging strategy – provides maximum energy gain
• Robins—
1. Concentrate on most productive
2. Remain until profitability falls
3. Leave patch when reaches average level
4. Ignore low productivity patches
American Robin, Turdus migratorius
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
XII. Plant defenses
1. Quantitative inhibitors—long-lived woody plants
• More expensive to plant• Reduce digestibility
2. Qualitative inhibitors—toxins• Interfere with metabolism• Low cost to plant
3. Structural defenses—interfere with herbivory
• Least costly defense
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