Predator Behavior Numerical Response – Predators will gather around a high density prey area ...
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Transcript of 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 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
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