Wk 9.doc

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29 Mar 2012
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TERMS AND EXAMPLES FOR WEEK 9
PREDATION DRAWBACKS:
1) TOUGH LIFE - STARVATION SUCCESS RATE OFTEN ONLY 10%
2) INJURY - PREY FIGHTS BACK WITH HOOVES CLAWS, TEETH
- ACCIDENTS DURING CHASE – HIT TREES, BUILDINGS, WINDOWS
3) POISONS IN SYSTEM - TOP OF FOOD WEB, ACCUMULATE TOXINS IN FOOD CHAIN
4) HUMAN PERSECUTIONCOYOTES, WOLVES, FOXES, BEARS – LITTLE PROTECTION
PREDATORS PLAY IMPORTANT ROLES IN ECOSYSTEMS
1) MAY HELP KEEP PREY NUMBERS LOWER -
2) IMPORTANT SELECTION PRESSURE - OPPORTUNISTICALLY SELECT WEAK, ILL, DEFORMED
INDIVIDUALS
PREDATION IS DIFFERENT THAN HUMAN HUNTING: HUNTING DOES NOT DISCRIMINATE BETWEEN
HEALTHY AND UNHEALTHY, GOOD GENES AND BAD GENES
SOME ANIMALS EAT THEIR PREY FROM INSIDE IT
TWO MAIN WAYS OF DOING THIS:
1) THE ANIMAL EATEN DIES
2) THE ANIMAL EATEN IS NOT HARMED
IN BOTH CASES, THE ANIMAL EATEN IS CALLED THE HOST. HOSTS ARE USUALLY A LOT
LARGER THAN THE ANIMALS THAT EAT THEM
PARASITIODS: KILL THE HOST
THE LARVAL FORM IS THE PARASITOID
CATERPILLARS AND SPIDERS ARE OFTEN THE HOSTS
TYPES OF PARASITOIDS:
A) ONES THAT USUALLY LAY EGGS ON LIVING HOST:
FLIES: FLESH FLIES, TACHINID FLIES
WASPS: ICHNEUMONS, BRACONIDS
B) ONES THAT STASH THEIR EGGS WITH PARALYZED PREY:
SPIDER WASPS, THREAD-WAISTED WASPS, DIGGER WASPS (CERCERIS)
PARASITOIDS LOCATE APPROPRIATE HOSTS BY:
1) VISUAL SEARCHING – BY FLESH FLIES, SPIDER WASPS
COMPLEX BEHAVIOURS: CAREFUL SELECTION - CATERPILLAR TOO LARGE OR SMALL IS PROBLEM
2) SOME BY SMELLS – PERHAPS DROPPINGS OF HOST OR FUNGUS ASSOCIATED WITH THEM
3) VIBRATIONS OF WOOD BORING BEETLES AS THEY CHEW
ICHNEUMONS – MEGARHYSSA ICHNEUMON WASPS LOCATE BY: ANTENNAE, FEET DETECT
VIBRATIONS; SOME LOCATE BY SMELL OF FUNGUS ASSOCIATED
WITH THE BEETLE GRUBS. ONCE THEY FIND A HOST, THEY DRILL INTO THE WOOD WITH AN
OVIPOSITOR
4) BY SOUND – TACHINID FLIES HEAR CRICKETS
5) A FEW FIND HOSTS BY PLANT CHEMICALS RELEASED WHEN LEAVES ARE EATEN BY INSECTS (RECALL
THIS WAS DISCUSSED UNDER PLANT DEFENCES)
PARASITISM = EATING A HOST WITHOUT KILLING IT; A ONE WAY RELATIONSHIP
PARASITES GENERALLY ARE MUCH SMALLER, ORDERS OF MAGNITUDE SMALLER, THAN THEIR HOSTS
TWO MAIN GROUPS:
ECTOPARASITES: LIVE ON THE OUTSIDE OF A HOST
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