Predator Behavior Numerical Response –

Predators will gather around a high density prey area

Predators “learn” where prey is (by experience or watching others)

Initially all predators benefit As more predators come…

= less prey = more predators competition Example: Grizzlies and salmon

Switching Switching

Predator “switches” prey Occurs when favored prey populations

drop Example:

Fox – typically hunt rabbits and quail. Will switch to rodents if quail populations drop

Grizzly Bears – eat salmon during their migration, then switch to berries as they become ripe

Optimal Foraging Strategy Survival Problem – must get more energy from food than energy used looking for it

Organisms that get most food w/ least effort = increase in fitness

Costs of foraging: Using energy Predators eating you Injury

costsbenefits

costs

benefitsNet energy loss(less fitness)

Net Energy Gain(more fitness)

Optimal Foraging “Rules” What the organism should do to maximize search

energy:1.eat most profitable prey = most energy intake2. feed more selectively when profitable prey is

available (ignore other prey species)3. include less profitable food only when more

profitable food is scarce4. ignore unprofitable food (even if common) when

profitable prey is common

BASICALLY – eat most profitable food as much as possible, for as long as possible. Don’t waste energy on less profitable food.

Foraging Strategy How organisms should maximize forage time:

1. Concentrate foraging activity in most productive patches (maximize efficiency)

2. Stay w/ productive patches until no longer profitable

3. Leave patch once it is no longer profitable

4. Ignore patches of low productivity (takes too long to get energy benefit)

Marginal value theorem - an animal should stay in a feeding patch until the expected net gain from staying declines to the expected net gain from traveling to and foraging in a new patch

Basically – stay in best patch and forage until predator could do better energetically by moving elsewhere

Foraging Strategy

Examples: (just pay attention) Bumblebee –

Bee should stay with productive patch of flowers until nectar is low

Then leave and find another productive patch

Fox – Stay in an area with high prey populations

until prey becomes scarce or competition becomes to intense

Predation risk Organisms risk predators while searching for food Must Balance:

When predators around – stay to less productive patches w/ more cover (thus less predators)

Example: Small birds vs. Eurasian Pygmy Owl

When voles present then owl doesn’t eat birds = so birds forage on out branches

When vole population low = owl switch to birds = so birds forage in more

dense areas to avoid owl

EnergyGains

PredationRisk

Foraging Strategies Generalists – Thrive in wide variety of habitats – able

access different resources Easily switch food source depending on

abundance Examples:

Most omnivores Raccoons Bears Humans

Foraging Strategies - Generalist

Raccoons Diet:

40% invertebrates 33% plant material 27% vertebrates

http://www.youtube.com/watch?v=p7Dv5_60Jd4

Foraging Strategies - Specialist

Specialists – Thrive in a narrow range of habitats

specific to their needs Able to exploit one or several food

sources - prey pops. usually stable (otherwise predators would go extinct)

Examples: Koala – only eat eucalyptus Owls

Foraging Strategies

Nocturnal predator small mammals roost in trees, silos,

barns face acts as parabolic

collector “silent” flight asymmetrical ear

openings

Optimal diet in the barn owl (Tyto alba), a SPECIALIST

When The Sun Comes Up! In Africa Every Morning A Gazelle

AwakensKnowing That It Must Outrun The Fastest Lion If It Wants To Stay Alive.

Every Morning A Lion Wakes Up KnowingThat It Must Run Faster Than The Slowest Gazelle Or It Will Starve To Death.

It Makes No Difference Whether You Are A Lion Or A Gazelle:

When The Sun Comes Up You Had Better Be Running. Source Unknown

In an evolutionary arms race --- prey evolve new defense and predator evolve way to defeat it

Ambush - Sit and wait for the prey to come Trap door spider, Frogs, alligators, insects – long

wait, low energy use Examples - Trapdoor Spider

http://www.youtube.com/watch?v=ySXCdcnKBgg&feature=related

http://www.youtube.com/watch?v=vZeplTuDz5g&NR=1

Active Searching – looking for prey More energy used = must eat bigger prey or more

readily available prey

Hunting Techniques

stalk and ambush tool usechase & pursuit communal

hunting intercept flight pathexhaust prey

Tool Use 1. Sea otter uses rocks to open shellfish

http://www.youtube.com/watch?v=MdRlD35rl3g

2. Egyptian vulture drops rocks on ostrich eggs to break them

3. Chimpanzees use twigs to access termites

4. Woodpecker finch of the Galapagos uses sticks to extract insect larvae

Crows using a tool http://www.youtube.com/watch?v=xwVhrrDvwPM

5. Archer fish spit water at insects on leaves above them http://www.youtube.com/watch?v=GhMi9Hw_wZ0&feature=channel

http://www.youtube.com/watch?v=fhBZ40jIo4Q

Hunting adaptations Fangs Claws Hearing (like owls) Hunting in groups Speed Coloration Bats - ultrasonic sounds to locate

prey Venom

Defense Adaptations Venom Armor Quills / Spines Hiding / Seeking cover Offense Safety in numbers Flee Confusion efforts