Transcript ppt

Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
- narrow: a “guild” is a group of
species that use the same
resources in the same way.
Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
-narrow: a “guild” is a group of
species that use the same
resources in the same way.
-complex: communities connected
by migration or energy flow
complex: communities connected by
migration or energy flow
Dragonflies eat pollinators and reduce
plant reproduction rates. Fish reverse
these effects, increasing plant
reproduction.
I. Introduction
A. Definitions of Community
B. Development of the Community Concept
Clements: “superorganism” concept
Discrete transitions
between communities
Development of the
‘climax’ community
through time, like
development of an
organism to the ‘mature’
adult
I. Introduction
A. Definitions
B. Development of the Community Concept
Clements: “superorganism” concept
Gleason: “individualistic” concept
“Communities” are just assemblages
of species that happen to have
overlapping ranges; but they are
responding independently to the
environment.
Whittaker – ’70’s:
Species respond
independently to
environmental gradients,
but steep gradients will
create abrupt transitions
between community
types.
For example, the
transition in community
type at a ‘serpentine
boundary’.
Serpentine soils have
very high chromium,
nickel, and magnesium.
There is usually an abrupt
change in soil
concentrations, creating
an abrupt change in
community type.
Where environmental
changes are more gradual,
community transitions will
be less abrupt, too.
For example, although each species
is most abundant under certain
moisture and elevation conditions in
the Smokies, they co-occur over a
wide range of conditions. Only their
relative abundances may vary.
I. Introduction
A. Definitions
B. Development of the Community Concept
Clements: “superorganism” concept
Gleason: “individualistic” concept
Whittaker: gradient analysis
Pickett and White: Patch-Dynamic Theory
Variation in community type may NOT just
be a function of changes in environmental
conditions; it may be function of changes in
disturbance regime, time since the last
disturbance, and successional stage of the
community.
Difference between pine and oak
communities may not be due to moisture; it
could be due to time since last fire.
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors – what is measured and compared?
1. Species Richness
Habitat 1
Habitat 2
species A
50
99
species B
50
1
Richness
2
2
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
1. Species Richness
Habitat 1
Habitat 2
2. Species Diversity
- relative abundance
species A
50
99
- Diversity Indices
species B
50
1
Richness
2
2
Simp. Div.
2
Simpson’s = 1/Σ(pi)2
1.02
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
1. Species Richness
Habitat 1
Habitat 2
2. Species Diversity
- relative abundance
species A
50
99
- Diversity Indices
species B
50
1
Richness
2
2
Simp. Div.
2
Simpson’s = 1/Σ(pi)2
3. Membership
- species list
1.02
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
1. Species Richness
2. Species Diversity
- relative abundance
- Diversity Indices
Simpson’s = 1/Σ(pi)2
3. Membership
4. Trophic Relationships
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
4. Trophic Relationships
- Food webs: define trophic relationships between species/taxa
- quantities:
nodes: species or 'trophic species' (ate and eaten by same group of
species) (S)
links: connections between trophic species (L)
connectance: C = L/(S(S-1)/2) tends to be constant across webs with
different richness... this is really the observed links over the maximum
number of links possible (S(S-1)/2)
4. Trophic Relationships
- Common Trophic Patterns:
As species richness increases, the number of trophic levels tends to increase and
the number of guilds tends to increase. But the links/species stays about the same
for a given community type.
- Omnivory is rare
- ‘Loops’ are rare
Community Ecology
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
D. Conceptual Models
D. Conceptual Models
1. Elton - numerical and biomass pyramids
E. Conceptual Models
1. Elton - numerical and biomass pyramids
Numerical and biomass pyramids can be "inverted":
- one tree can be preyed upon by thousands of insect herbivores
E. Conceptual Models
1. Elton - numerical and biomass pyramids
Numerical and biomass pyramids can be "inverted":
- one tree can be preyed upon by thousands of insect herbivores
- a lower trophic level can support more biomass at a higher level IF the rate
of biomass production in lower level is high
E. Conceptual Models
1. Elton - numerical and biomass pyramids
Numerical and biomass pyramids can be "inverted":
- one tree can be preyed upon by thousands of insect herbivores
- a lower trophic level can support more biomass at a higher level IF the rate
of biomass production in lower level is high
- but a productivity pyramid (new biomass/area/time) can't be permanently
inverted
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
- energetic conversion rates determine biomass transfer:
- endotherm food chains are short; only 10% efficient
Only 10% of the biomass
consumed by herbivores is
converted into herbivore
biomass that is available to
predators.
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
- energetic conversion rates determine biomass transfer:
- endotherm food chains are short; only 10% efficient
- ectotherm food chains can be longer,
because energy is transfered more
efficiently up a food chain (insects 50% efficient).
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
- energy available in lower level will determine the productivity of
higher levels... this is called "bottom-up" regulation.
not enough energy to support
another trophic level
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
3. Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
3. Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
something else...predation?
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
3. Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
something else ....predation?
- If herbivore populations are kept low by predators, they must be the
variable limiting predator populations - as food. SO:
Top Pred's: Limited by Competition
Herbivores: Limited by Predation
Plants: Limited by Competition
E. Conceptual Models
1. Elton - '20's - numerical and biomass pyramids
2. Lindeman - 40's - energetic perspective
3. Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
predation.
- If herbivore populations are kept low by predators, they must be the
variable limiting predator populations - as food. SO:
Top Pred's: Limited by Competition
Herbivores: Limited by Predation
Plants: Limited by Competition
Community structured by "top-down effects" and ‘trophic cascades’
Community Ecology
I. Introduction
A. Definitions
B. Development of the Community Concept
C. Key Descriptors
D. Conceptual Models of Trophic Structure
E. Empirical Tests of Trophic Models
E. Empirical Tests of Trophic Models
1. Leibold et al. (1997)
As primary productivity increases,
herbivore biomass increases,
consistent with bottom-up theory.
When fish were added, herbivores
(zooplankton) declined and
phytoplankton were released from
herbivory and increased; indicating
top-down effects once the third level
(predators) were added.
E. Empirical Tests of Trophic Models
1. Leibold et al. (1997)
2. Hansson et al. (1998)
Adding fish reduces
zooplankton and
RELEASES
phytoplankton (“topdown”)….
No
effect
Adding nutrients in 3-level systems pumped up zooplantkon, NOT
phytoplankton (consistent with L-V predator-prey models and
bottom up effects).
No
effect
In 4-level systems, adding nutrients pumped up FISH, who ate the
zooplantkton, and RELEASED algae. Alternating effects as topdown predict.