Chapter 53 (pgs. 1174 – 1196) Community Ecology AP minknow The difference between a fundamental...
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Transcript of Chapter 53 (pgs. 1174 – 1196) Community Ecology AP minknow The difference between a fundamental...
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.
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 top-down 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 interaction
•The various animals and plants surrounding this watering hole
•Are all members of a savanna community in southern Africa
• 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
53.1: A community’s interactions include competition, predation, herbivory, symbiosis, and disease
Competition• Interspecific
competition– 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 PrincipleThe competitive exclusion principle
States that two species competing for the same limiting resources cannot coexist in the same place
Click on picture to watch movie
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
When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.
The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realizedniche of Chthamalus much smaller than its fundamental niche.
RESULTS
CONCLUSION
Ocean
Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland.
EXPERIMENT
In nature, Balanus fails to survive high on the rocks because it isunable 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.
Low tide
High tide
Chthamalusfundamental niche
Chthamalusrealized niche
Low tide
High tide
Chthamalus
Balanusrealized niche
Balanus
Ocean
A. insolitususually percheson shady branches.
A. distichus perches on fence posts
and other sunny
surfaces.
A. distichus
A. ricordii
A. insolitusA. christophei
A. cybotesA. etheridgei
A. alinigar
Resource Partitioning• Resource partitioning is the differentiation
of niches– That enables similar species to coexist in a
community
G. fortis
Beak depth (mm)
G. fuliginosa
Beak depth
Los Hermanos
Daphne
Santa María, San Cristóbal
Sympatric populations
G. fuliginosa, allopatric
G. fortis, allopatric
Per
cent
ages
of
indi
vidu
als
in e
ach
size
cla
ss
40
20
0
40
20
0
40
20
0
8 10 12 14 16
Figure 53.4
Character Displacement
• 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
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
• 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
(a) Hawkmoth larva
(b) Green parrot snake
Figure 53.7a, b
In Müllerian mimicry
Two or more unpalatable species resemble each other
(a) Cuckoo bee
(b) Yellow jacketFigure 53.8a, b
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
Community 1
A: 25% B: 25% C: 25% D: 25%
Community 2A: 80% B: 5% C: 5% D: 10%
D
C
B
A
Figure 53.11
A community with an even species abundance
Is more diverse than one in which one or two species are abundant and the remainder rare
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 chainsQuaternary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers
Carnivore
Carnivore
Carnivore
Herbivore
Plant
Carnivore
Carnivore
Carnivore
Zooplankton
Phytoplankton
A terrestrial food chain A marine food chainFigure 53.12
– Link the trophic levels from producers to top carnivores
– Help to show the flow of energy through an ecosystem
Food WebsHumans
Baleen whales
Crab-eater seals
Birds Fishes Squids
Leopardseals
Elephant seals
Smaller toothed whales
Sperm whales
Carnivorous plankton
Euphausids (krill)
Copepods
Phyto-plankton
Figure 53.13
– Is a branching food chain with complex trophic interactions
Food Webs
• Food webs can be simplified– By isolating a portion of a community that
interacts very little with the rest of the community
Sea nettle
Fish larvae
ZooplanktonFish eggs
Juvenile striped bass
Figure 53.14
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
High (control)
Medium Low
Productivity
No. of species
No. of trophic links
Num
ber
of
spec
ies
Num
ber
of
trop
hic
links
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Figure 53.15
Reduction of energy input in a tree-hole community (Queensland, Australia) had a direct affect on the length of the food chain
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– Exhibit their role as a keystone
species in intertidal communities
(a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates.
With Pisaster (control)
Without Pisaster (experimental)
Num
ber
of s
peci
es
pres
ent
0
5
10
15
20
1963 ´64 ´65 ´66 ´67 ´68 ´69 ´70 ´71 ´72 ´73
(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
Figure 53.17 Food chain beforekiller whale involve-ment in chain
(a) Sea otter abundance
(b) Sea urchin biomass
(c) Total kelp density
Num
ber
per
0.25
m2
1972 1985 1989 1993 19970
2
468
10
0
100
200
300
400
Gra
ms
per
0.25
m2
Ott
er n
umbe
r (%
max
. co
unt)
0
40
20
60
80
100
YearFood chain after killerwhales started preyingon otters
– Shows the effect the otters haveon ocean communities
• Observation of sea otter populations and their predation
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– That have
positive effects on the survival and reproduction of some of the other species in the community
Salt marsh with Juncus (foreground)
With Juncus
Without Juncus
Nu
mb
er
of
pla
nt
spe
cie
s
0
2
4
6
8
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
0 100 200 300 400
Rainfall (mm)
0
25
50
75
100
Per
cen
tag
e o
f he
rbac
eous
pla
nt c
over
Bottom-Up
Top-Down
Rainfall determines community controls in this Chilean desert comm.
(Non-El Nino) Dry
(El Nino) Wet
Pollution– Can affect community
dynamics
• But through biomanipulation– Polluted communities can be
restored
Fish
Zooplankton
Algae
Abundant
Rare
RareAbundant
Abundant
Rare
Polluted State Restored State
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 burned forseveral years has a high propor-tion of detritus (dead grass).
(b) During the burn. The detritus serves as fuel for fires.
(c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.
•The intermediate 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
Figure 53.22a, b
(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.
(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
(b) Dryas stage
(c) Spruce stage(d) Nitrogen fixation by
Dryas and alder increases the soil nitrogen content.
So
il n
itro
ge
n
(g/m
2)
Successional stagePioneer Dryas Alder Spruce
0
10
20
30
40
50
60
(a) Pioneer stage, with fireweed dominant
Further Your Information
• Read 53.4 and 53.5 Page 1175 Page 1180