Predation

Predation takes a variety of forms

• Carnivory (narrowest view)
• Cannibalism
• Parasitism (slowly eating another)
• Parasitoidism (wasp stings host (paralyzes)--> lays eggs inside--> eggs hatch and eat host)
• Herbivory (broadest view)

Each population...

• Controls the other

Functional response

• the relationship between the average number of prey eaten by each predator per unit time vs. prey density

Type I Pattern

• Capture rate is constant (linear line)
• Increase predator density
• prey mortality is density dependent (prey are not near "K")
• prey do not satiate predator
• characteristic of passive predators (don't invest energy to capture prey)
• Examples:
• Long search times (Spiders & webs)
• Filter feeders (coral reefs and anemones)
• Some active predators

Type II Pattern

• Per capita capture rate increases in a decelerating fashion
• Predator satiation OR time to handle prey is a constant so only a max amount can be taken
• Handling time is composed of:
• search time
• capturing time
• eating time
• digesting time
• Predator controlling the prey?? NO

Type III Pattern (S shaped curve)

• PREDATOR MIGHT BE CONTROLLING THE PREY POPULATION
• Rate at first is low, then increases, then decreases
• Low density hard to find
• lack of a search image (can't recognize something familiar)
• Higher density increase capture rate
• Rate then slows due to handling time OR predator satiation (full of nutrient or physically full)
• Predation could limit prey population; % of prey taken increases
• But if prey density increases, prey satiate the predator

Prey Switching

• As prey density goes down, predators may switch to alternate prey
• Prey switching is variable because
• Alternate prey may be:
• less palatable, less nutritious, more energy to process, harder to handle/capture

Numerical Response

• Predator response:
• As prey increases, predator population should:
• increase through births
• decrease mortality (fastest--> population grows bigger)
• immigrate

Coevolution

• Foraging by prey is risky business:
• Fight or flight response
• Prey evolve to avoid predators
• Predators evolve to find prey
• ---Chemical defense (poisons, noxious chemicals) Ex: monarch butterflies, skunks
• ---Cryptic colorations (camouflage)
• ---Deimatic (bluff) displays (false eyes on moth wings)
• ---Aposematic (warning colors) (coral snake)

Mimicry

• ---Batesian mimicry
• nonpoisonous copy (Ex: papilio butterfly-nonpoison-mimics danaidae, king snake-nonpoison-mimics coral)
• ---Mullerian mimicry
• many poison species with similar color patterns (Ex: danaidae butterfly-poison, coral snake-poison)
• ---Aggressive mimicry
• used by predators (Ex: bolas spider-->imitates moth scent to attract moths, flounder--> blends into sand, frog fish--> looks like floating algae and uses camo to sneak up on prey, saber-tooth fish--> looks like cleaner wrasse to kill fish

Protective Armor

• Armadillo, porcupine, pangolin

Behavioral defense

• Defense of young
• Musk ox form a circle around young to keep wolves away from young
• Killdeer have a broken wing display

Reproductive timing

• Reproduce when predators are not present OR
• Young are produced in large quantities which creates predator satiation
• Walnut caterpillars and salmon fry; 'R' strategy

Plant antiherbivory defenses

• Mechanical
• Chemical
• Ant defense

Plant mechanical defense

• Cacti--> spines, thorns, prickles, hairs

Plant chemical defense

• Toxins cause death
• Reduces digestibility--> slower development, increased predation
• Toxin examples:
• Guarana--> caffeine
• Ferns--> cyanide
• Kava--> kava lactones (depressant, liver damage, brain damage)
• Milkweed--> cardiac glycosides (heart arrhythmia)
• Reduce digestibility:
• Oaks & Maples--> Tannins (tan hides)
• There are chemical variations through seasons; they produce different chemicals at different times; fern is an example

Ant Defense

• Harbor ants to protect them herbivores
• Ex: whistling thorn acacia tree; ants protect tree from giraffes

Predators have evolved hunting tactics

• Hunting tactics optimizes energy and nutrient uptake
• Tactics:
• Ambush
• Stalking
• Pursuit

Ambush

• Lying in wait
• Komodo dragon/alligators/crocs/gaboon vipers/chameleons
• Max. time input
• low frequency of success
• minimal energy input
• often used by ectotherms

Stalking

• Systematically search, find prey, and quick attack
• Leopards/Coyotes/herons/cranes/tigers
• long search time
• pursuit time minimal
• moderate frequency of success
• moderate energy input
• many endotherms

Pursuit

• Go to prey and attack
• Cheetahs/Swallows/bats/lions
• short search time
• pursuit is lengthy
• high frequency of success 1/10
• high energy input
• many endotherms/heterotherms

Predators use foraging strategy

• Strategies--> a plan to achieve a goal
• Tactics--> an action which helps to enact a strategy
• Foraging tactics-->
• optimize nutrient intake
• energy expenditure,
• minimize predation upon the forager
• Optimal foraging theory-->how an organism should behave to optimize nutrient intake and energy expenditures
• Optimal diet
• Optimal patch
• Optimal allocation of time to patch
• Optimal pattern of movement
• Optimal forage period
• Optimal foraging group size

Optimal diet

• Highest energy intake, least energy expenditure
• Ex:
• Pied wagtails--> don't eat the most common seed
• Humans--> processed food

Optimal patch

• Forage in those patches that are better than average
• Ex:
• Prairie falcon forage in patches w/ greater than 65 ground squirrels in a patch

Optimal allocation of time to patch

• Move when cost to obtain prey increases
• Ex:
• Kestrels forage for short time then move

Optimal pattern of movement

• Forage to REDUCE path crossing to minimize energy expenditures

Optimal forage period

• Forage when prey is available
• Ex:
• Robins eat morning worms near surface

Optimal foraging group size

• Match size of predator group to prey group size; forage in groups that optimize capture rate
• Ex:
• Hyenas forage in groups of size similar to prey