Transcript Introduction to Community Ecology

Communities
What is a community?
A simple definition: “A collection
of interacting species found in the
same habitat at the same time”
What is a community?
What is a plant community?
What is a plant community?
Generally restricted
to a consideration
of a subset of the
Plantae
All plants
Vascular plants
Grasses
What is a plant community?
Assemblages: a set of
phylogentically
related organisms
occurring in the same
geographic area
What is a plant community?
Guilds or
functional groups
“sets of organisms that
use biotic or abiotic
resources in a similar
way”
What is a plant community?
Local Guilds
• Trees in a forest
• Herbs on a forest floor
• Algae in a pond
What is a plant community?
Ensembles
• Vascular plants at
Doolittle Prairie
• Mosses growing
on a log
• Epiphytic orchids
growing on a tree
branch
General Approaches to
the Study of Plant Communities
• Classification  taxonomy
Classification:
the “Association” as an example
• Classification  taxonomy
Artemesia tridentataAgropyron
Agropyron
- Festuca
What is an Association?
Required characteristics
• Consistent floristic composition
• Uniform physiognomy
• Occurs in a particular habitat
(i.e., determined by environment)
Consistent floristic composition
Consistent floristic composition
What types of species are useful
in classification?
Extremely common?
No – not habitat
specific enough
Rare?
No – not reliable
Moderately common?
Perhaps, if exhibit
high habitat fidelity
What is an Association?
Required characteristics
• Consistent floristic composition
• Uniform physiognomy
• Occurs in a particular habitat
(i.e., determined by environment)
Physiognomy
Form, structure or appearance
of a plant community
Physiognomy
Physiognomy
What is an Association?
Required characteristics
• Consistent floristic composition
• Uniform physiognomy
• Occurs in a particular habitat
(i.e., determined by environment)
Habitat Specificity
• Classification  taxonomy
Utility of the Taxonomic Approach
• Can categorize or name “communities”
• Useful for mapping
• Ecologically meaningful?
General Approaches to
the Study of Plant Communities
• Classification  taxonomy
• Comparison
– Convergent evolution
under similar environments
Convergent evolution
Monument
Valley, U.S.A
Kalahari of
South Africa
General Approaches to
the Study of Plant Communities
• Classification  taxonomy
• Comparison
– Convergence in community structure
under similar environmental conditions
– Comparison of communities under locally
varying environmental conditions
– Patterns of diversity
General Approaches to
the Study of Plant Communities
• Classification  taxonomy
• Comparison
• Process level studies
– Succession
– Response to disturbance
– Assembly rules
Are Plant Communities
Real?
An historically
important debate
Organismic vs. Individualistic
Viewpoints
The Organismic Viewpoint of Clements
• Plants are highly coadapted to their
environments
 +/+ and 0/0 interactions predominate
 Long mutual history of organisms
• Sum > Parts
 Emergent properties
• Community as superorganism
 Species:Community ::
Tissues:Organism
Predictions of the Organismic Viewpoint
• Parallel distribution patterns along gradients
• Narrow ecotones
The Individualistic Viewpoint of Gleason
• Species are distributed according to
individual characteristics
• -/- interactions predominate
• Community is not an integrated
organism
 No emergent properties
• Communities are an artificial construct
of convenience
Predictions of the Individualistic Viewpoint
• Independent distributions along gradients
• Few discernable ecotones
Resolving the Debate
An approach developed by Curtis
and Whittaker
Studies of species distributions relative
to environmental gradients
(2) Arrange data in a plot:
species along an ordered
gradient
Location Moisture
#1
3.2
#2
0.8
#3
7.6
#4
5
Abundance
(1) Sample sites for criticial
environmental conditions
and species composition
Species a
Abundance
10
4
1
3
Species a
Moisture
The Evidence
Tree species
along a moisture
gradient in
Wisconsin
(Curtis)
The Evidence
Plant species
with altitude in
the Great Smoky
Mountains
(Whittaker)
The Evidence
Plant species
with altitude in
the Great Smoky
Mountains
(Whittaker)
The Bottom Line
The individualistic hypothesis is a more
appropriate characterization of
ecological reality