Remember what a COMMUNITY is?

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Behavior between species COMMUNITIES SPECIES
INTERACTIONS
Remember what a COMMUNITY is? How about an
ECOSYSTEM?
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Some common types of species interactions
Predation
Herbivory
Symbiosis
Competition
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Three types of SYMBIOSIS
barnacles on whale
tapeworm
Commensalism
Parasitism
cleaner wrasse
Mutualism
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Plants, herbivores predators form food chains
and "food webs"
are eaten by
are eaten by
PRODUCERS
PRIMARY CONSUMERS
SECONDARY CONSUMERS
(often there are more consumers above secondary)
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Example of an even longer food chain
PRIMARY CONSUMER
SECONDARY CONSUMER
TERTIARY CONSUMERS
PRODUCERS
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Takes a lot of producers to feed 1 consumer...
why?
The 10 rule of BIOMASS
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Food webs can be complex
concept of "ecological niche"
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Because of COMPETITION each species has its own
NICHE
ECOLOGICAL NICHE the way a species "makes its
living" the "job" it has What exactly does it
eat? What eats it? What habitat does it need?
(etc.)
No two species that live in the same area can
have exactly the same ecological niche
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DOMINANT species
The most abundant species On land usually is
whichever tree/grass can out-compete the
others In marine ecosystems sometimes is a
filter-feeder (not a plant)
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KEYSTONE species Some examples
Low abundance but has unusually big impact on the
ecosystem Without it the whole ecosystem will
often "collapse"
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Example marine tidepools
MUSSELS
SEA STARS
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"Keystone Predators" module
Three seaweeds (algae) that photosynthesize
Three SESSILE consumers
Three MOTILE consumers
Nori seaweed
Mussel
Whelk (kind of snail)
Acorn Barnacle
Chitons
Black pine
Starfish (Pisaster)
Gooseneck Barnacle
Coral weed
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KEYSTONE species Some examples
Low abundance but has unusually big impact on the
ecosystem Without it the whole ecosystem will
often "collapse"
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Starfish are the only predator thats keeping the
dominant mussels in check
MUSSELS
STARFISH
are eaten by
Mussels can out-compete all other sessile
creatures But starfish eat mussels STARFISH ARE
KEYSTONE SPECIES
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Gray wolf another top predator
ELK
GRAY WOLF
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Example Yellowstone
After eradication of wolf, aspen and cottonwood
trees started declining why?
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Elk eat aspen cottonwood saplings in
winter(often GIRDLE them)
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1995 - Wolves reintroduced to Yellowstone
Animals were wild Canada wolves (not zoo
wolves) captured 1995-96
19
Started hunting elk again...
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...and moose
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...and bison
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Ecological effects

• Expected
• Elk down
• Cottonwood aspen up
• Riparian areas up
• Unexpected
• Elk behavior also changes
• COYOTE DOWN
• RED FOX up
• BEAVER up, PONDS up
• PRONGHORN way up

23
The ecosystem was more complicated than we
thought...... and wolves have huge effects
Wolf actually doesnt eat coyote - just kills
them because of COMPETITION