Introduction to Ecology
CERC Certificate Program
Columbia University
Session 3 – Community Ecology
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Ecological Footprint Exercise
• We have an impact on the Earth
– Responses?
– Critiques of the calculations?
Population Growth Exercise
• What did you find?
– Describe the curves – what was happening when?
– When would you get population oscillations in the
Logistic Model?
– Approximate K for humans?
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Exponential Population
Growth Equation Derivation
• The equation for population change over a unit t (time)
N=t +NB
+B
I - +DI -–D
E–then
•N
N
E N = B + I - D – E
t+1/=t
o+
• Simplify the equation
– Assume a closed population
– Eliminate migration (I, E)
• N
N // t
t == B
No- +DB - D
– Growth rate r = (B/N) – (D/N)
• N / t = (r)(No)
– This is the basic exponential growth equation
Logistic Population Growth
Equation Derivation
• Add the Carrying Capacity (K)
– how?
• N / t = (r)(No)
– Base Expon. Equation
• N / t = (r)(No)(1-(N/K))
– Base Logistic equation
Growth Matters!
• r-selected species
– Why most weeds are weedy
– Edge species are typically
r-selected
– Invasive species are often rselected
Growth Matters!
• K-selected species
– Why we don’t get
many species of oaks
in most young forests?
– Climax communities
– Susceptible to
habitat fragmentation
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Why is This Field Important?
• Useful for conserving entire communities
• Repopulating barren lands
• Determining most important species to
conserve
• Predicting how communities will recover,
after disturbance
• Predicting community resilience to
disturbance
• Quantifying what is present for
conservation and where it would be
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Community Definition
• “an association of
interacting populations,
usually defined by the
nature of their
associations or the habitat
they use”
• Key features:
– Several species
– One area
What Structures a
Community?
• Abiotic
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Climate
Latitude
Proximity to Ocean
Disturbances (abiotic)
• Biotic
– Interspecific Interactions
• Keystone Species
– Disturbances (biotic)
– (Intraspecific Interactions?)
Types of Interspecific Interactions
No interaction
Allelopathy
Commensalism
Mutualism
Competition
Predation
Parasitism
Species 1
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Species 2
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Niches
• Definition?
• 1. The ecological
role played by a
species in a
community
• 2. An n-dimensional
hypervolume
– Huh?
Niche =
N-dimensional Hypervolume
• Dimensions are the
limiting factors
pH
• pH, soil type,
humidity, temperature,
nesting space, mates,
parasites, etc.
• Niche use determines
community formation
pH
temperature
– sharp boundaries
– abrupt ecotones
– distinct associations
between species
• Open
– boundaries are vague,
gradual
– little or no association
between species
abundance
• Closed
abundance
General Types of
Communities
Abundance of
a single species
geographic range
geographic range
How Do Communities Form?
• Neutral Assembly
– Species in a community come together not necessarily
due to the presence of other species
– Due to other idiosyncratic, species-specific influences
• Community Assembly Rules
– Repeatable patterns of how communities form
– Sequence of adding species is important
– Deterministic patterns, including max # of spp present
Can this be tested?
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Island Biogeography
• Full Title: “Equilibrium Theory of
Island Biogeography”
• Assertions re: # species:
– Near > Far
– Bigger > Smaller
– There is an equilibrial number of
species
• Advocates for CAR?
Island Biogeography Research
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Florida Keys - mangrove islands
Gassed several islands to kill all insects on mangroves
Observed return rates of species
Counted number and trophic type
Occurred in early 1970’s
Island Biogeography Results
• Size of Island (longhorn beetles)
– Species-Area
Relationship
• Equilibrial
Theory (insects)
Island Biogeography
Conclusions
• Supported main assertions
• Assertions re: # species:
– Near > Far
– Bigger > Smaller
– There is an equilibrial number of
species
• Spawned a great deal of
additional research by many others
– One of two main proponents
(Simberloff) no longer agrees with
equilibrial assertion
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Keystone Species
• The most important species
– Structures the community
– What is the origin of the term?
• Contributes greatest amount to ecosystem
functioning
– Controlling herbivores
• Terminal Predators are most commonly thought of here
– Decomposition
– Produces greatest amount of biomass?
Keystone Species
• Usually thought of as Strong interactors
– Tightly woven into the fabric of the food web
– The species that is the very strongest
interactor
• Definition #2:
– The species that, when removed, leads to a
total breakdown of the food web
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Succession Definitions
• Chronological
distribution of
organisms within an
area
• The sequence of
species within a
habitat or community
through time
• Shared:
– Time
– Single area
Succession Types – by Habitat
• Primary
– New habitat from
barren ground
•Secondary
–Modified habitat in already
areas with biotic growth
Succession Types – by Process
• Degradative
– Consumption of a finite resource
• Allogenic
– Requires ongoing extrinsic environmental changes
• Autogenic
– Intrinsic factors within the community
Applications of Succession
• Can you think of any?
• Examples:
–Gauging timber harvests or fisheries harvests
–Dating deposits (bog people)
–Forensic Entomology
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Measuring Biodiversity
• Aspects of biodiversity to
measure?
• Possibilities
–Richness
–Abundance
–Diversity (interaction of
richness & abundance)
–Trophic Levels
–Feeding Guilds
–Taxonomic Diversity
Diversity Indices
• Used to compare sites or evaluate a single one
through time
• Many many many types
• Main ones:
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Shannon (diversity)
Simpson (diversity)
Rarefaction (richness)
Sorenson (comparative diversity)
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Global Distribution of
Biodiversity
• Greatest in areas where NPP is greatest
– Terrestrial: toward Equator - Why?
– Aquatic: near shore, marine upwellings – Why?
Community Ecology
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Goals for the day
Why is this field important?
What is a community: Community Classifications
Island Biogeography
Keystone Species
Succession
Measuring Biodiversity
Global Distribution of Biodiversity
Community Stability and Diversity
Relationship Between Community
Diversity and Stability
• Stability components
– Resistance
– Resilience
– Recovery speed
• Biodiversity has been
thought to influence
Stability
– Croplands – Unstable
– Tropics – Stable
• Jury still out
– preliminary work seems to
support this
Assignment for Next week:
• Forensic Entomology!
– Learn more about the application of community ecology
and succession to solving crimes
• Instructions are all online, and available here
• Turn in next week via email
– We will discuss it then
Proximate Ecological Fields
- Next Week:
• Trends down pyramid:
– Increase in geographic scale
Population
– From single species to multiple
species
Community
– Increasing number of ecological
factors that may be influential
Ecosystem
– Decreasing certainty in results
Next Week: The Tour of
Ecology Continues
• Population ecology
• Community ecology
• Ecosystem ecology
– Next week’s emphasis
• Conservation Issues