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AP Biology
Community Ecology
ƒ Community
‹
all the organisms that live together in a
place
ƒ interactions
ƒ Community Ecology
‹
organism
population
community
Community Ecology
To answer:
In what way do the
populations
l ti
interact?
i t
t?
study of
interactions
among all
populations
in a common
environment
ecosystem
biosphere
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Niche
ƒ An organism’s niche is its ecological role
‹
habitat = address vs. niche = job
Niche & competition
ƒ Competitive Exclusion
‹
High tide
Competitive Exclusion
If Species 2 is removed,
then Species 1 will occupy
Low tide
whole tidal zone.
But at
lower depths Species 2
out-competes Species 1,
excluding it from its
potential (fundamental)
niche.
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Species
i 1
Chthamalus sp.
Species 2
Fundamental Realized
niches
niches
Semibalanus sp.
Resource partitioning
Reduce competition through microhabitats
“the ghost of
competition past”
No two similar species can occupy the
same niche at the same time
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Interspecific interactions
ƒ Symbiotic interactions
‹
competition (-/-)
ƒ compete for limited resource
ƒ competitive exclusion!
predation / parasitism (-/+)
‹ mutualism (+/+)
‹
ƒ lichens (algae & fungus)
‹
commensalism (+/0)
ƒ barnacles attached
to whale
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Symbiosis
mutualism
+/+
What relationship is this?
…not very funny
for a clown fish
commensalism
+/0
predation
+/- competition
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-/-
Predation drives evolution
Anti-predator adaptations
ƒ Hide from predators
ƒ Predators adaptations
‹
locate & subdue prey
‹
ƒ Prey adaptations
‹
‹
elude & defend Predation provides
horns speed
horns,
speed, coloration
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avoid detection
camouflage
ƒ Warn p
predators
a strong selection
pressure on both
b th
prey & predator
advertise how undesirable
you are as prey
‹ aposematic coloration
‹
spines, thorns, toxins
ƒ apo = away & sematic = sign/meaning
ƒ Batesian mimicry
ƒ Mullerian mimicry
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Convergent evolution
Defense mechanisms
ƒ Camouflage
‹
Mimicry
Batesian mimicry
palatable or harmless species
mimics a harmful model
cryptic coloration
whipporwill
frog
green parrot snake
lizard
hawkmoth larvae
lizard
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toad
Hawkmoth larva puffs up to
look like poisonous snake
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Convergent evolution
Batesian mimicry
Mullerian mimicry
two or more protected
species look like each other
cuckoo bee
Monarch male
Viceroy male
poisonous
edible
Which is the moth
bee?
fly vs.vs.
thethe
bee?
yellow jacket
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fly
bee
moth
bee
Common warning coloration
- group defense?
- predators may evolve innate avoidance
Mullerian mimicry
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What kind of mimicry?
ƒ Aposematic species come to resemble each other
black, red,
orange & yellow
means:
DON’T EAT ME!
Coral snake
is poisonous
King snake is not
Red on yellow, poison fellow;
red on black, safe from attack
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Coevolution in Community
ƒ Predator-prey relationships
ƒ Parasite-host relationships
ƒ Flowers & pollinators
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Characterizing a community
ƒ Community structure
‹
species diversity
‹
composition
ƒ how many different species
ƒ dominant species
ƒ most abundant species
or highest biomass
(total weight)
ƒ keystone species
ƒ changes over time
Š succession
Long term evolutionary adjustments between species
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Species diversity
The impact of reduced biodiversity
greater diversity = greater stability
compare these communities
ƒ Greater biodiversity
offers:
more food
resources
‹ more habitats
‹ more resilience
in face of
environmental
change
‹
suburban
lawn
agricultural
“monoculture”
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Keystone species
Pisaster ochraceous
ƒ Influential ecological role
exert important
regulating effect
on other species
in community
‹ keystone
species
increases
diversity
in habitat
Keystone species
Sea otter is a
keystone
predator in
North Pacific
‹
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“old field”
ƒ Irish potato famine
ƒ 1970 US corn crop failure
Sea star
diversity increases
diversity decreases
mussels out-compete
other species
Washington coast
Keystone species
Beaver is a
keystone species in
Northeast & West
dams
transform flowing streams into ponds creating new habitat
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What is the
impact of the
Orca whale?
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Ecological succession
ƒ Sequence of community changes
‹
transition in species composition over time
‹
usually after a disturbance
ƒ years or decades
Mt.
Helens
APSt.
Biology
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Primary succession
ƒ Begins with
Secondary succession
ƒ Existing community cleared,
virtually
lifeless area
without soil,
then…
but base soil is still intact
burning releases
nutrients formerly
l k d up in
locked
i the
th
tissues of tree
bacteria
lichens &
mosses
‹ grasses
‹ shrubs
‹ trees
{
make
soil
‹
‹
the disturbance
starts the process
of succession
over again
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Succession of species
pioneer species
compete well in high sunlight
What causes succession?
ƒ Tolerance
‹
‹
early species are weedy r-selected
tolerant of harsh conditions
ƒ Facilitation & Inhibition
grasses
lichens & mosses
more shade tolerant species
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climax forest
shade tolerant species
stable community
bushes & small trees
trees
Climax forest
ƒ Plant community dominated by trees
ƒ Representing final stage of natural
‹
early
l species
i facilitate
f ilit t habitat
h bit t changes
h
ƒ change soil pH
ƒ change soil fertility
ƒ change light levels
‹
allows other species
to out-compete
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Climax forest
The species mix of
climax forest is
dependent on the
abiotic factors of
the region
succession for specific location
‹
‹
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stable plant community
remains essentially unchanged in species
composition as long as site remains undisturbed
ƒ birch, beech, maple,
hemlock
ƒ oak, hickory, pine
taiga
ƒ solar energy levels
ƒ temperature
ƒ rainfall
ƒ fertility & depth of soil
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temperate deciduous forest
birch, beech, maple, hemlock
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Disturbances as natural cycle
ƒ Disturbances are often necessary for
Fire climax species
Jack Pine
adaptations to survive
and reproduce in areas
than experience
frequent fires
community development & survival
- release nutrients
- increases biodiversity
fire climax forests
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- increases habitats
- rejuvenates community
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When people don’t learn ecology!
Don’t blow
your top!
Ask
Questions!
Building homes in fire climax zones
preventing fires
makes next year’s
fire much worse!
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