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