Transcript 19 Lecture 2006

OUR Ecological Footprint - 6
1. Recycle; pay tax for it.
2. Live near work;
Ride bike; minimize car use.
3. Buy energy-efficient furnace.
4. Programmable thermostat: winter/summer
5. Turn off lights when leave room; unplug appliance
6.
Next week’s Lab:
Data Analysis in Computer Lab
Data Entry to Excel: Each individual
MUST enter all data before lab
SDP2 Manuscript
Introduction
Methods
Literature Cited
1 draft ONLY
Ch 23: Community Development
Ch 21: Community Structure
Objectives
•
•
•
•
•
•
•
•
How are communities measured/compared?
Is the community a natural unit?
Are communities in equilibrium? stable?
How strong are connections among species?
How are food febs measrued/compared?
Do complex food webs aid stability?
What controls abundance within trophic levels?
Do keystone species aid stability?
• Next lecture: How do communities change
following disturbance?
What is a community? assemblage of
species that co-occur in the same place.
What is a community here? How many are
there?
How many are here? How abrupt are
boundaries of these communities?
How can community structure be quantified
and compared?
***
Which variables can be used to describe the
species diversity of a community?
Which community is more diverse?
• Species richness
• Species relative
abundance
Species richness (# of species) = S
• S varies with sample size so…
• Compare S by rarefaction:
equal-sized subsamples randomly drawn.
Measures of community structure
•
Species richness: # of species BUT
species differ in abundance and thus in role
•
Species diversity:
weight species by their relative abundance
•
Simpson’s index: D = 1 /  pi2
p = proportion of each species in total
sample
•
Shannon-Wiener index: H' = -  pi ln pi
Calculate Species Diversity:
Species No. Ind. pi
pi2
1
5
.25
.0625
2
4
.20
.0400
3
3
.15
.0225
4
4
.20
.0400
5
4
.20
.0400
Total (N) 20
1.00 ∑=.205
• D = 1/ ∑pi2 = 1/.205 = 4.878
• H' = -∑ pi ln pi = 1.5965
ln pi
pi ln pi
-1.386
-.3465
-1.609
-.3218
-1.897
-.2846
-1.609
-.3218
-1.609
-.3218
∑= -1.5965
Comparisons of diversity indices among
communities.
C1
C2
C3
C4
C5
•***What factors increase species diversity?
• more species.
• less difference in relative abundance
among species.
‘Community’ has many meanings:
• Spatially defined
• Functionally defined --> focus on
interactions
• Community = an association of
interacting populations
• First: focus on spatially defined…
Is the community a natural unit of
ecological organization?
Closed vs. open community structure…
Holistic
Individualistic
Soil conditions reflecting underlying
geology may cause prominent community
boundaries = ecotone.
Concentrations of soil minerals change
sharply across ecotone.
Replacement of species across an ecotone.
Historical arguments…
What is the ‘nature’ of the community?
• Clements:
•
holistic concept
•
superorganism/interdependent
•
whole greater than sum of parts
•
closed with discrete boundaries
•
emphasis descriptive and on
classification
Gleason (UI!):
•
•
•
•
•
individualistic concept
haphazard assemblages of species
not interdependent
open with no natural boundaries
emphasis on community dynamics
and functional organization
• Which concept has most support?
Whittaker (UI!): gradient analysis
How are species distributed along a
physical gradient?
• Open or closed?
• Ecotones?
• Continuum?
• Most communities
are open…
• species distribute
independently of
other species.
Continuum concept: Within broadly defined
habitats, species replace one another continuously
along gradients of physical conditions.
***Do these data support the ‘continuum
concept”?
***Do these data support a stable
(equilbrium) or transient (non-equilbrium)
view of the community?
Question: Do identical communities
develop in identical environments?
• ‘Clemensian’ hypothesis: yes
• ‘Gleasonian’ hypothesis: no
• Experimental set-up?
• ‘Clemensian’ prediction: Identical plankton
communities will develop in all ponds.
•‘Gleasonian’ prediction: Different plankton
communnities will develop in different
ponds.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
2. Examine water samples;
3. ID each speciesPresent in each pond.
What is
conclusion?
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• What is the ‘nature’ of the community?
• How tightly connected are species?
• Are communities stable or transient?
OPEN
Later models
Redundancy
Non-equilibrium
CLOSED
Rivet
Equilibrium
How can community structure be quantified
and compared?
***
Which variables can be used to describe the
species diversity of a community?
Which community is more diverse?
• Species richness
• Species relative
abundance
Species richness (# of species) = S
• S varies with sample size so…
• Compare S by rarefaction:
equal-sized subsamples randomly drawn.
Measures of community structure
•
Species richness: # of species BUT
species differ in abundance and thus in role
•
Species diversity:
weight species by their relative abundance
•
Simpson’s index: D = 1 /  pi2
p = proportion of each species in total
sample
•
Shannon-Wiener index: H' = -  pi ln pi
Calculate Species Diversity:
Species No. Ind. pi
pi2
1
5
.25
.0625
2
4
.20
.0400
3
3
.15
.0225
4
4
.20
.0400
5
4
.20
.0400
Total (N) 20
1.00 ∑=.205
• D = 1/ ∑pi2 = 1/.205 = 4.878
• H' = -∑ pi ln pi = 1.5965
ln pi
pi ln pi
-1.386
-.3465
-1.609
-.3218
-1.897
-.2846
-1.609
-.3218
-1.609
-.3218
∑= -1.5965
Comparisons of diversity indices among
communities.
C1
C2
C3
C4
C5
•***What factors increase species diversity?
• more species.
• less difference in relative abundance
among species.
Community: functionally defined
How strong are the connections among
species in a community?
• Rivet model
•
tight linkage in ‘web of life’
•
obligate associations of species
•
or obligate exclusion of species
• Redundancy model
•
loose ‘web of life’
•
most species have no impact on other
species
•
species and ecological processes are
redundant
***What are conservation implications of the
two contrasting models?
• Would focus be on community
dynamics or single-species dynamics?
• In which model are keystone species
important?
Feeding relationships organize
communities in food webs.
Communities of similar diversity can have
very different food webs.
***What changes with increased food web
complexity? What doesn’t change?
# trophic levels
3
4
6
Variables that quantify food webs:
• # species
• # guilds (groups of species with different
feeding or foraging ecology)
• Total # feeding links
• # feeding links per species
• Connectance = # interactions/total possible
•
= # interactions/[S(S-1)/2]
• Linkage density = # interactions/# species
Does greater complexity of food web increase
community stability?
***Does food web complexity lead to
increased community stability?
• Pro:
• alternative resources--->less dependent on
fluctuations in any one resource
• energy can take many routes --> disruption
of one pathway shunts more energy to
another
• Con:
• more links may create pervasive,
destabilizing time lags in population
processes
Question: Which are more stable when
disturbed: species-rich or less-diverse
communities?
Hypothesis: Resistance to disturbance
increases with increasing species richness.
Null hypothesis: No relationship exists
between resistance and species richness.
Experimental Design?
Prediciton: Plots with more species before
drought are more resistant to change.
Null prediction: All plots have similar
resistance regardless of species richness.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
What is the conclusion?
Different approaches to depict food webs--->
show different ways in which populations
influence one another.
Connectedness
Energy flow
Functional
What influences abundance with each trophic
levels?
H1: predation (top-down control)
H2: production by plants (bottom-up control).
Trophic
cascade
links all
trophic
levels.
Bottom-up
Top-down
Trophic cascade: indirect effects of
consumer-resource interactions extended
through additional trophic levels of the
community.
• top-down effect
• consumers depress size of trophic
level immediately below them, which
indirectly increases populations two
tropic levels below.
Keystone species: non-redundant, key
species in maintaining community
stability and diversity
• can be:
•
plants
•
herbivore
•
top predator
If a beetle is the keystone species,
then…removal of the beetle will ---> lower
species diversity.
Objectives
•
•
•
•
•
•
•
•
How are communities measured/compared?
Is the community a natural unit?
Are communities in equilibrium? stable?
How strong are connections among species?
How are food webs measrued/compared?
Do complex food webs aid stability?
What controls abundance within trophic levels?
Do keystone species aid stability?
• Next lecture: How do communities change
following disturbance?
Vocabulary
Chapte r 21 Community Structure
biological communit y
holistic concept
species richne ss
open community
gradient analysis
energy flow webs
linkage density
trophic cascade
dominant s
relative abund ance
rarefaction
species diversity*
rivet model
organismic concept*
guilds
ecotones
food web
functional webs
keystone species
top-down control
species-area relationship*
SimpsonΥs index
equilibrium force*
species evenness*
redundancy model
individua list concept*
closed community
continuum concept
connectednesswebs
connectance
bottom -up control
diversity indices
Shannon -Wiener inde x
non-equilibrium force*
species richne ss*