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Predator Behavior  Numerical Response –  Predators will gather around a high density prey area  Predators “learn” where prey is (by experience or watching.

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Presentation on theme: "Predator Behavior  Numerical Response –  Predators will gather around a high density prey area  Predators “learn” where prey is (by experience or watching."— Presentation transcript:

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2 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

3 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

4 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 costs benefits costs benefits Net energy loss (less fitness) Net Energy Gain (more fitness)

5 Optimal Foraging “Rules”  What the organism should do to maximize search energy: 1. eat most profitable prey = most energy intake 2. feed more selectively when profitable prey is available (ignore other prey species) 3. include less profitable food only when more profitable food is scarce 4. 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.

6 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

7 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

8 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 Energy Gains Predation Risk

9 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

10 Foraging Strategies - Generalist  Raccoons  Diet:  40% invertebrates  33% plant material  27% vertebrates  Jd4 Jd4

11 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

12 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

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14 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 Knowing That 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

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

16  Ambush -  Sit and wait for the prey to come  Trap door spider, Frogs, alligators, insects – long wait, low energy use  Examples - Trapdoor Spider   Active Searching – looking for prey  More energy used = must eat bigger prey or more readily available prey

17 Hunting Techniques stalk and ambushtool use chase & pursuitcommunal hunting intercept flight path exhaust prey

18 Tool Use  1. Sea otter uses rocks to open shellfish   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   5. Archer fish spit water at insects on leaves above them  

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

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


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