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