predator behavior numerical response – –predators will gather around a high density prey area...

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

• Examples: – 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

3-9 ATB

• What are some costs / dangers associated with foraging?

• Today:– Generalists / specialists– Owl pellets?

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 - rodents

Foraging Strategies

• Primarily a nocturnal predator

• Can locate prey using only sound

• Hunts small mammals (mostly voles)

• Roost in trees, silos, barns

• Face acts as parabolic sound collector

• “silent” flight

• Asymmetrical ear openings

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

http://www.youtube.com/watch?v=yps7pgq1TAk

3-10 ATB

• What is the difference between a generalist and a specialist?

• Today:– Discuss coevolution

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

Knowing 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

Coevolution

• Coevolution = – hosts and parasites (or predator and prey)

become locked in a duel of escalating adaptations

– Has been called an “evolutionary arms race” – Each evolves new responses to the other– It may not be beneficial to the parasite to kill its

host

• 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 use

chase & pursuit communal hunting

intercept flight path

exhaust prey

• Tool Use

• How could it help the species?– Tool allowed organism to access more food – = higher fitness

3-14 ATB

• What is coevolution?

• Today:– Discuss predator adaptations

Tool Use Examples• 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– http://www.youtube.com/watch?v=5Cp7_In7f88

• 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

3-15 ATB

• How do you think tool use evolved?

• Objectives:– Discuss defense adaptations – cryptic

coloration, warning coloration, etc– Start “Kings of Camouflage”– “Eternal Arms Race”

• http://www.youtube.com/watch?v=3zTR3-N4ObM&feature=related

• http://www.youtube.com/watch?v=25sHr44Xy9M&feature=related

• http://www.youtube.com/watch?v=x69DNj0qPwU&feature=related