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Community Ecology
The
study of the interactions
between the species in an
area.
Community Hypothesis
1. Individualistic
2. Interactive
Individualistic
Hypothesis
H.A.
Gleason
Community as a chance
assemblage of species
because of similar abiotic
requirements.
Interactive Hypothesis
F.E.
Clements
Community as a linked
assemblage of species that
function as an integrated
whole.
Predictions
Individualistic
- fuzzy borders
Interactive - sharp borders
Robert Whittaker – tested the
two ideas against each other.
Results
If
abiotic factors form a
continuum, then borders are
fuzzy.
Individualistic Hypothesis is
correct.
Comment
Abiotic
factors may form
sharp borders.
Ex: soil types
Result – the Community may
look very much like the
Interactive Hypothesis.
Interspecific
Interactions
Interaction
between species.
May be positive, negative, or neutral.
Ex:
1. Coevolution
2. Predation
3. Mimicry
4. Competition
5. Symbiosis
Coevolution
 When
two
species have
reciprocal
evolution to
each other.
 Ex:
 Flowers
and
their pollinators.
Predation (+/-)
Predator
and
prey
relationships.
Ex – Lynx and
Hares
Predation
Often
results in interesting
defenses or adaptations.
Ex:
Plant
defenses
Cryptic coloration
Aposematic coloration
Cryptic Coloration
A
passive defense where the
prey is camouflaged against
its environment.
Aposematic Coloration
The
use of
conspicuous
colors in toxic
or unpalatable
organisms to
warn off
predators.
poison arrow frogs
Mimicry
Defense
mechanism where the
mimic has a resemblance to
another species, the model.
Types:
Batesian
Mullerian
Batesian Mimicry
Palatable
species mimics an
unpalatable model.
Hawk moth larva
Snake
Mullerian Mimicry
Two
unpalatable species
resemble each other.
Cuckoo Bee
Yellow Jacket
Competition
When
two species rely on the
same limiting resource.
Intraspecific competition
usually more severe than
Interspecific competition.
Why?
Competitive Exclusion
Principle
Predicts
that two species
with the same requirement
can not co-exist in the same
community.
One species will survive and
the second will go extinct.
Ecological Niche
The
n-hyperspace of
requirements for a species.
How a species “fits into” an
ecosystem.
Species can not have niche
overlap, the Competitive
Exclusion Principle
Niche Types
1. Fundamental - what a
species is theoretically
capable of using.
2. Realized - what a species
can actually use.
Resource Partitioning
A
way that species avoid
niche overlap by splitting up
the available resources.
Ex: Anolis lizards
A. distichus
A. insolitus
Symbiosis
When
two different species
live together in direct contact.
Types:
1. Parasitism
2. Commensalism
3. Mutualism
Parasitism (+/-)
Parasite
harms the host.
Parasites may be external or
internal.
Well adapted parasites don't
kill the host.
Parasitic behavior: A female
Nasonia vitripennis laying a clutch of eggs into
the pupa of a blowfly (Phormia regina)
Commensalism (+/o)
One
partner
benefits while
the other is
unchanged.
Ex. – Cattle
and Egrets
Mutualism (+/+)
Both
partners
benefit from
the interaction.
Ex:
Pollinators
and flowers
Acacia Tree and Ants
Succession
Changes
in
species
composition
over time.
Succession Stages
Sere:
unstable stage usually
replaced by another
community.
Climax: stable stage,
self-reproducing.
Succession Types
1. Primary
2. Secondary
Primary Succession
Building
a community from a
lifeless area.
Ex: volcanic islands
glaciated areas
road cuts
Comment
The
first example of primary
succession was worked out on
the Indiana Dunes.
Stages:
Open
Beach
Beach Grasses
Conifers (Junipers and Pines)
Oaks
Beech-Maple forest (Climax)
Secondary Succession
Where
a community has been
disturbed and the soil is
mostly intact.
Ex:
Cutting
down a forest
Blow-outs on the Dunes
Causes of Succession
1. Autogenic Factors
2. Allogenic Factors
Autogenic Factors
Changes
introduced by the
organisms themselves.
Ex: toxins
acids
Allogenic Factors
Outside
disturbances
Ex: Fire
Floods
Prairie Succession in
Oklahoma - Stages
1. Annual Weeds
2. Triple-Awn Grass
3. Bunch Grass
4. Climax: Tall-grass Prairie
Annual Weed Stage
Lasts
2-3 years.
Very robust growth (1-2 m).
Species: Sunflower
Pigweed
Lamb's Quarter
Annual Weed Stage
Annual Weed Stage
Annual Weed Stage
Annual Weed Stage
Triple-Awn Stage
Lasts
10 - 50 years.
Very poor growth (5-12 cm).
Species: Triple-Awn Grass
Triple Awn Stage
Question
How
can Triple-Awn replace
the more robust annual
weeds?
Allelopathy
The
release of chemical
inhibitors into the
environment.
Sunflower: autotoxic
Triple Awn: tolerant
Triple-Awn
Inhibits
Nitrogen fixing
bacteria species
Result: soil N stays low
which stalls succession.
Bunch Grass Stage
Lasts
20 - 100 years.
Good growth (30-50 cm).
Species: Little Bluestem
Bunch Grass Stage
Succession Causes
Bunchgrass
eventually
shades out Triple-Awn,
releasing the inhibition of the
nitrogen fixers.
Result: soil fertility increases,
allowing the next group of
species to invade.
Climax Prairie Stage
Lasts
centuries if maintained
by fire.
High growth (up to 2 meters).
Species: Big Bluestem,
Indiana Grass, Switch Grass,
Little Bluestem
Tall Grass Prairie
Tall Grass Prairie
Question
Stages
3 and 4 are the best
for cattle grazing.
Normal succession takes
20 - 50+ years.
Can the time needed for
restoring the prairie be
decreased?
Solution
more N to soil (NH4+)
Seed climax species
Result: prairie in 3-10 years.
Maintain the prairie by
burning.
Add
Upland, IN Prairie
Upland, IN Prairie
Upland, IN Prairie
Point
If
you understand the causes
and controlling factors of
succession, you can
manipulate them.
Productivity Lab Report
Graph
and data are on
BlackBoard.
Graph - Analysis of results:
7 questions
DO Readings – Analysis of
results: - 2 questions
Biogeography
Study
of the past and present
distributions of individual
species and communities.
Range Limitations
1. Lack of dispersion.
2. Failure to survive in new
areas.
3. Retraction from former
range area.
Proof
Fossil
Evidence
Pollen Studies
Transplant Experiments
Islands
Special
cases in
Biogeography.
Must be colonized from other
areas.
Island Species Factors
Island
size.
Distance from mainland.
Island Size
Small
islands hold few
species.
Why?
Fewer niches available for
species to occupy.
Distance from Mainland
Closer
islands have more
species.
Why?
Easier for colonization.
Comment
Islands
tend to have high
numbers of Endemic species
Why?
Adaptive Radiation and
Evolution of new species.
Summary
Know
the two hypothesis of
community structure.
Know the various types of
interspecific interactions.
Know the Competitive
Exclusion Principle and
Niche Concept.
Summary
Know
some examples and
causes of succession.
Know how island
communities are shaped.