Transcript Slide 1

Chapter 53 (pgs. 1174 – 1196)
Community Ecology
AP minknow
•The difference between a fundamental niche and a realized niche
•The role of competitive exclusion in interspecific competition.
•The symbiotic relationships of parasitism, mutualism, and
commensalism.
•The impact of keystone species on community structure.
•The difference between primary and secondary succession.
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What Is a Community?
1.Explain the relationship between species richness and relative
abundance.
2.Define and compare the individualistic hypothesis of H.A. Gleason
and the interactive hypothesis of F.E. Clements with respect to
communities.
Interspecific Interactions and Community Structure
3.List four possible specific interactions and explain how the
relationships affect the population densities of the two species.
4.Explain how interspecific competition may affect community
structure.
5.Describe the competitive exclusion principle and explain how
competitive exclusion may affect community structure.
6.Define an ecological niche and restate the competitive exclusion
principle using the niche concept.
7.Explain how resource partitioning can affect species diversity.
8.Define and compare predation, herbivory, and parasitism.
9.Relate some specific predatory adaptations to the properties of the
prey.
10.Describe the defense mechanisms that evolved in plants to
reduce predation by herbivores.
• 11.Explain how cryptic coloration and warning coloration aid an
animal in avoiding predators.
• 12.Distinguish between Batesian mimicry and Müllerian
mimicry.
• 13.Describe how predators use mimicry to obtain prey.
• 14.Distinguish among endoparasites, ectoparasites, and
pathogens.
• 15.Distinguish among parasitism, mutualism, and
commensalism.
• 16.Distinguish between a food chain and a food web. Describe
the factors that transform food chains into food webs.
• 17.Describe two ways to simplify food webs.
• 18.Summarize two hypotheses that explain why food chains are
relatively short.
• 19.Explain how dominant and keystone species exert strong
control on community structure. Give several examples of
each.
• 20.Describe and distinguish between the bottom-up and topdown models of community organization. Also describe some
models that are intermediate between those two extremes.
• Disturbance and Community Structure
• 21.Describe how disturbances affect community structure and
composition. Illustrate this point with several well-studied
examples.
• 22.Give examples of humans as widespread agents of
disturbance.
• 23.Describe and distinguish between primary and secondary
succession.
• 24.Describe and distinguish among facilitation, inhibition, and
toleration.
• 25.Describe the process and pattern of succession on
moraines in Glacier Bay.
• Biogeographic Factors Affecting the Biodiversity of
Communities
• 26.Describe and distinguish between species richness and
relative abundance.
• 27.Describe the data necessary to measure biodiversity.
• 28.Describe and explain how species richness varies along
the equatorial-polar gradient.
• 29.Define the species-area curve.
• 30.Explain how species richness on islands varies according
to island size and distance from the mainland.
What Is a Community?
• A biological
community
– Is an
assemblage of
populations of
various species
living close
enough for
potential
•The various animals and plants surrounding
interaction this watering hole
•Are all members of a savanna
community in southern Africa
53.1: A community’s interactions include competition,
predation, herbivory, symbiosis, and disease
• Populations are
linked by
interspecific
interactions
– That affect the
survival and
reproduction of
the species
engaged in the
interaction
– These interaction
can have
differing effects
on the
populations
involved
Competition
• Interspecific
competition
Click on picture to watch movie
– Occurs when
species compete
for a particular
resource that is in
short supply
• Strong
competition can
lead to
competitive
exclusion
– The local
elimination of one
of the two
competing species
The Competitive Exclusion
Principle
The competitive exclusion principle
States that two species competing
for the same limiting resources
cannot coexist in the same place
Ecological Niches
• Habitat - the area where an
organism lives, including the
biotic and abiotic factors that
affect the organism.
• Resources - any necessity of
life, such as water, nutrients,
light, food, or space.
Habitat + Resources = ?????
• The ecological niche
– Is the total of an organism’s use of
the biotic and abiotic resources in
its environment
Warbler Niches
• Can you have two separate organisms
occupying the same exact niche???
NO
•The niche concept allows restatement of the
competitive exclusion principle
•Two species cannot coexist in a
community if their niches are identical
However, ecologically similar species
can coexist in a community
– If there are one or more significant difference
in their niches
As a result of
competition
A species’
fundamental
niche may
be different
from its
realized
niche
Ecologist Joseph Connell
studied
EXPERIMENT two barnacle
speciesBalanus balanoides and
Chthamalus stellatus that have a
stratified distribution on rocks along
the coast of Scotland.
When Connell removed
Balanus from the lower strata, the
Chthamalus population spread into
that area.
RESULTS
High tide
High tide
Chthamalus
Balanus
Chthamalus
realized niche
Chthamalus
fundamental niche
Balanus
realized niche
Ocean
Ocean
Low tide
Low tide
In nature, Balanus fails to survive high
on the rocks because it is
unable to resist desiccation (drying out)
during low tides. Its realized niche is
therefore similar to its fundamental niche.
In contrast, Chthamalus is usually
concentrated on the upper strata of rocks.
To determine the fundamental of niche of
Chthamalus, Connell removed Balanus
from the lower strata.
The spread of Chthamalus
when Balanus was removed indicates
that competitive exclusion makes the
realized
niche of Chthamalus much smaller
than its fundamental niche.
CONCLUSION
Resource Partitioning
• Resource partitioning is the differentiation
of niches
– That enables similar species to coexist in a
A. insolitus
community
usually perches
on shady
branches.
A. ricordii
A. distichus
perches on
fence posts
and other
sunny
surfaces.
A. insolitus
A. alinigar
A. distichus
A. christophei
A. cybotes
A. etheridgei
Character Displacement
G. fortis
G. fuliginosa
• In character
displacement
–
–
There is a tendency for
characteristics to be
more divergent in
sympatric populations
of two species than in
allopatric populations of
the same two species
Sympatric population
– geographically
overlapping
Allopatric population
– geographically
isolated
Figure 53.4
Santa María, San Cristóbal
40
Percentages of individuals in each size class
–
Beak depth
Sympatric
populations
20
0
Los
Hermanos
40
G. fuliginosa,
allopatric
20
0
Daphne
40
G. fortis, allopatric
20
0
8
10
12
Beak depth (mm)
14
16
Predation
• Predation refers
to an interaction
– Where one
species, the
predator, kills and
eats the other,
the prey
•Feeding adaptations of
predators include
•Claws, teeth,
fangs, stingers, and
poison
•Animals also display
•A great variety of
defensive
adaptations
Defensive Adaptations
•
•
•
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Cryptic coloration
Aposematic coloration
Batesian mimicry
Mullerian mimicry
Cryptic coloration, or camouflage
Makes prey difficult to spot
Figure 53.5
Aposematic coloration
– Warns predators to stay away from prey
– Poison arrow frog
Figure 53.6
In Batesian mimicry
– A palatable or harmless species mimics an
unpalatable or harmful model
(b) Green parrot snake
Figure 53.7a, b
(a) Hawkmoth larva
In Müllerian mimicry
Two or more unpalatable species resemble
each other
(a) Cuckoo bee
Figure 53.8a, b
(b) Yellow jacket
Herbivory
• Herbivory, the process
in which an herbivore
eats parts of a plant
– Has led to the
evolution of plant
mechanical and
chemical defenses and
consequent
adaptations by
herbivores
Community Interactions
• Symbiosis – any relationship in which two
species live closely together.
– There are three types of Symbiosis
• Parasitism
– Disease
• Mutualism
• Commensalism
Parasitism
• In parasitism, one organism, the parasite
– Derives its nourishment from another
organism, its host, which is harmed in the
process
Parasitism
• Parasitism
exerts
substantial
influence on
populations
– And the
structure of
communities
– Parasite
– Host
• Endoparasites
• Ectoparasites
• Parasitoidism
Disease
• The effects of disease on populations and
communities
– Is similar to that of parasites
Pathogens, disease-causing
agents
Are typically bacteria,
viruses, or protists
Mutualism
• Mutualistic symbiosis, or mutualism
– Is an interspecific interaction that benefits
both species
Figure 53.9
Commensalism
• In commensalism
– One species
benefits and the
other is not
affected
• Commensal
interactions have
been difficult to
document in nature
– Because any close
association
between species
likely affects both
species Figure 53.10
Interspecific Interactions and
Adaptation
• Evidence for coevolution
– Which involves reciprocal genetic change by
interacting populations, is scarce
•However, generalized
adaptation of organisms to
other organisms in their
environment
•Is a fundamental
feature of life
53.2: Dominant and keystone species exert
strong controls on community structure
• In general, a small number of
species in a community
– Exert strong control on that
community’s structure
• Dominant Species – Those species
in a community that have the highest abundance
or highest biomass. These species exert a
powerful control over the occurrence and
distribution of other species.
• Keystone Species – A species that is
not necessarily abundant in a community yet
exerts strong control on community structure by
the nature of its ecological role or niche
Species Diversity
• The species
diversity of a
community
– Is the variety of
different kinds of
organisms that make
up the community
– Has two components
• Species richness
– Is the total number of
different species in
the community
• Relative abundance
– Is the proportion
each species
represents of the
total individuals in
the community
Species Diversity
• Two different communities
– Can have the same species richness, but a different
relative abundance
A
B
A community with an even
species abundance
Is more diverse than one in
which one or two species
are abundant and the
remainder rare
Figure 53.11
C
D
A: 25%
Community 1
B: 25%
C: 25%
D: 25%
A: 80%
Community 2
B: 5%
C: 5%
D: 10%
Trophic Structure
• Trophic structure
– Is the feeding relationships between organisms
in a community
– Is a key factor in community dynamics
• We can look at trophic structure through
– Food Chains
– Food Webs
Food chains
– Link the trophic
levels from
producers to top
carnivores
– Help to show the
flow of energy
through an
ecosystem
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Carnivore
Primary
consumers
Zooplankton
Herbivore
Primary
producers
Plant
Figure 53.12
A terrestrial food chain
Phytoplankton
A marine food chain
Humans
Food Webs
– Is a branching
food chain with
complex
trophic
interactions
Smaller toothed
whales
Baleen
whales
Crab-eater seals
Birds
Sperm
whales
Elephant
seals
Leopard
seals
Fishes
Squids
Carnivorous
plankton
Copepods
Euphausids
(krill)
Phytoplankton
Figure 53.13
Food Webs
• Food webs can be simplified
– By isolating a portion of a community that
interacts very little with the rest of the
community
Juvenile striped bass
Sea nettle
Fish larvae
Figure 53.14
Fish eggs
Zooplankton
Limits on Food Chain Length
• Each food chain in a food web
– Is usually only a few links long
• There are two hypotheses
– That attempt to explain food chain length
•The energetic
hypothesis
•suggests that the
length of a food chain Is
limited by the
inefficiency of energy
transfer along the chain
•The dynamic stability
hypothesis
•Proposes that long food
chains are less stable than
short ones
Limits on Food Chain Lengths
• Most of the available data
– Support the energetic hypothesis
6
Figure 53.15
No. of species
5
No. of trophic
links
4
5
4
3
3
2
2
1
1
0
0
High
(control)
Medium
Productivity
Low
Number of trophic links
Reduction of
energy input
in a tree-hole
community
(Queensland,
Australia) had
a direct affect
on the length
of the food
chain
Number of species
6
Species with a Large Impact
• Certain species have an especially large impact
on the structure of entire communities
– Either because they are highly abundant r because
they play a pivotal role in community dynamics
• Dominant Species
• Keystone Species
Dominant Species
• One hypothesis suggests that dominant
species
– Are most competitive in exploiting limited
resources
• Another hypothesis for dominant species
success
– Is that they are most successful at avoiding
predators
Keystone Species
• Field studies of sea
stars
Number of species
present
– Exhibit their role as a
keystone species in intertidal
communities
With Pisaster (control)
20
15
10
Without Pisaster (experimental)
5
0
1963 ´64 ´65 ´66 ´67 ´68 ´69 ´70 ´71 ´72 ´73
(a)
The sea star Pisaster
ochraceous feeds
preferentially on mussels
but will consume other
invertebrates.
(b) When
Pisaster was removed from an
intertidal zone, mussels eventually
took over the rock face and eliminated
most other invertebrates and algae. In
a control area from which Pisaster
was not removed, there was little
change in species diversity.
Keystone Species
• Observation of sea otter populations and
their predation
Otter number
(% max. count)
100
– Shows the
effect the
otters have
on ocean
communities
80
60
40
20
0
(a) Sea otter abundance
Grams per
0.25 m2
400
300
200
100
0
Number per
0.25 m2
(b) Sea urchin biomass
10
8
6
4
2
0
1972
1985
1989
Year
Figure 53.17
Food chain before
killer whale
involvement in chain
(c) Total kelp density
1993
1997
Food chain after
killer
whales started
preying
on otters
Ecosystem “Engineers”
(Foundation Species)
• Some organisms exert their influence
– By causing physical changes in the
environment that affect community structure
Foundation Species
• Some
foundation
species act as
facilitators
Number of plant species
– That have
positive effects
on the survival
and
reproduction of
some of the
other species in
the community
8
6
4
2
0
With
Juncus
Salt marsh with
Juncus (foreground)
Without
Juncus
Conditions
Bottom-Up and Top-Down Controls
• The bottom-up model of community
organization
– Proposes a unidirectional influence from lower
to higher trophic levels
• In this case, the presence or absence of
abiotic nutrients
– Determines community structure, including the
abundance of primary producers
Bottom-Up and Top-Down Controls
• The top-down model of community
organization
– Proposes that control comes from the trophic
level above
• In this case, predators control herbivores
– Which in turn control primary producers
Long-term experiment studies have
shown
That communities can shift periodically from
bottom-up to top-down
100
Rainfall
determines
community
controls in this
Chilean desert
comm.
(Non-El Nino)
Dry
(El Nino) Wet
Percentage of
herbaceous plant cover
Bottom-Up
75
50
25
Top-Down
0
0
100
200
Rainfall (mm)
300
400
Pollution
– Can affect community
dynamics
• But through biomanipulation
– Polluted communities can be
restored
Polluted State
Fish
Restored State
Abundant
Rare
Zooplankton
Rare
Abundant
Algae
Abundant
Rare
53.3: Disturbance influences species
diversity and composition
• Decades ago, most ecologists favored the
traditional view
– That communities are in a state of equilibrium
• However, a recent emphasis on change
has led to a nonequilibrium model
– Which describes communities as constantly
changing after being buffeted by disturbances
What Is Disturbance?
• A disturbance
– Is an event that
changes a community
– Removes organisms
from a community
– Alters resource
availability
Fire
- Is a significant disturbance in most
terrestrial ecosystems
– Is often a necessity in some communities
(a) Before a controlled burn.
A prairie that has not
(b) During the burn. The
burned for
detritus
several years has a high
serves as fuel for fires.
proportion of detritus (dead grass).
•The intermediate
(c) After the burn.
Approximately one month
after the controlled burn,
virtually all of the biomass
in this prairie is living.
disturbance hypothesis
•Suggests that moderate levels of disturbance can foster higher
species diversity than low levels of disturbance
The large-scale fire in Yellowstone
National Park in 1988
– Demonstrated that communities can often
respond very rapidly to a massive disturbance
(a) Soon after fire. As this photo taken soon after the fire shows,
the burn left a patchy landscape. Note the unburned trees in the
distance.
Figure 53.22a, b
( b) One year after fire. This photo of the same general area taken the
following year indicates how rapidly the community began to
recover. A variety of herbaceous plants, different from those in the
former forest, cover the ground.
Human Disturbance
• Humans
– Are the most widespread
agents of disturbance
• Human disturbance to
communities
– Usually reduces species
diversity
• Humans also prevent
some naturally occurring
disturbances
– Which can be important to
community structure
Ecological Succession
• Ecosystems are constantly in flux.
Ecological Succession – is the series of
predictable changes that occurs in an
ecosystem over time.
• Primary succession
• Secondary succession
Primary Succession
• Occurs on surfaces
where no soil exists,
usually after a volcanic
eruption. (receding
glaciers)
– 1. Bare rock community is
populated by an pioneer
species (first species to
populate an area). Usually
lichens (fungus and alga).
– 2. Pioneer species help to
form soil and puts
nutrients into soil.
– 3. Plants begin to grow 
then off to the races
Secondary Succession
• Occurs in an community where everything has been
removed but the soil.
• What could cause the process of primary succession to
begin?
Succession on the moraines in
Glacier Bay, Alaska
– Follows a predictable pattern of change in
vegetation and soil characteristics
(a) Pioneer stage, with fireweed dominant
(b) Dryas stage
60
Soil nitrogen
(g/m2)
50
40
30
20
10
0
Pioneer Dryas Alder Spruce
Successional stage
(d) Nitrogen fixation by
Dryas and alder
increases the soil
nitrogen content.
(c) Spruce stage
Further Your Information
• Read 53.4 and 53.5 Page 1175  Page
1180