Community Ecology

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Community Ecology
Community Ecology
AP Chapter 54

• AP Chapter 54

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Calculator Policy

• A four-function calculator (with square root) is
  permitted on both the multiple-choice and
  free-response sections of the AP Biology Exam
  since both sections contain questions that
  require data manipulation. No other types of
  calculators, including scientific and graphing
  calculators, are permitted for use on the exam.
  Four-function calculators have a one line display
  and a simple layout of numeric keys (e.g., 09),
  arithmetic operation keys (e.g., , -, , and ),
  and a limited number of special-use keys (e.g.,
  , /-, C, and AC). Simple memory buttons like
  MC, M, M-, and MR may also be included on a
  four-function calculator. Scientific calculators
  have a more complicated, multi-row layout that
  includes various special-use keys, including ones
  for trigonometric and logarithmic functions such
  as SIN, COS, TAN, TRIG, LOG, and LN. In contrast
  to scientific calculators, four-function
  calculators do not include trigonometric and
  logarithmic functions, statistical capabilities,
  or graphing capabilities. Students may bring up
  to two four-function calculators (with square
  root) to the exam.

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What is a community?

• A biological community is an assemblage of
  populations of various species living close
  enough for potential interaction

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What are the types of interactions?

• relationships between species in a community
  interspecific interactions
• Examples are competition, predation, herbivory,
  and symbiosis (parasitism, mutualism, and
  commensalism)
• Interspecific interactions can affect the
  survival and reproduction of each species, and
  the effects can be summarized as positive (),
  negative (), or no effect (0)

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Competition

• Interspecific competition (/ interaction)
  occurs when species compete for a resource in
  short supply
• Strong competition can lead to competitive
  exclusion, local elimination of a competing
  species
• The Gause competitive exclusion principle states
  that two species competing for the same limiting
  resources cannot coexist in the same place

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Ecological Niches

• The total of a species use of biotic and abiotic
  resources is called the species ecological niche
  
• An ecological niche can also be thought of as an
  organisms ecological role
• It is the functional position of an organism in
  its environment, comprising its habitat and the
  resources it obtains, periods of time it is
  active, etc.

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Adaptations for Locomotion Biorhythms Tolerance Pr
edator avoidance Reproduction feeding
Physical conditions Substrate Humidity Sunlight Te
mperature Salinity pH Exposure Attitude depth
Resources offered by the habitat Food Shelter Mati
ng sites Nesting sites Predator avoidance
Other organisms
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• Ecologically similar species can coexist in a
  community if there are one or more significant
  differences in their niches
• Resource partitioning is differentiation of
  ecological niches, enabling similar species to
  coexist in a community

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Fig. 54-2
A. insolitus usually perches on shady branches.
A. distichus perches on fence posts and other
sunny surfaces.
A. ricordii
A. insolitus
A. aliniger
A. christophei
A. distichus
A. cybotes
A. etheridgei
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• The full range of environmental conditions under
  which an organism can exist is its fundamental
  niche.
• Due to interactions and evironmental pressures,
  organisms are usually forced to occupy a niche
  that is narrower than thistheir realized niche.

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Fig. 54-3
EXPERIMENT
High tide
Chthamalus
Chthamalus realized niche
Balanus
Balanus realized niche
Ocean
Low tide
RESULTS
High tide
Chthamalus fundamental niche
Ocean
Low tide
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• Question Two species of Anolis lizards are
  often found perched and feeding in the same
  trees, with species I in the upper and outer
  branches, and species II occupying the shady
  inner branches. After removing one or the other
  species in test trees, an ecologist observes the
  following results Species I is found throughout
  the branches of trees in which it is now the sole
  occupant. Species II is still found only in the
  shady interior when it is the sole occupant.
  What do these results indicate about the niches
  of these two species?

The realized niche of Species I is smaller than
its fundamental niche when it is in competition
with SpeciesII.
Species I
Species IIs fundamental and Realized niche are
the same.
Species II
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Predation

• Predation (/ interaction) refers to interaction
  where one species, the predator, kills and eats
  the other, the prey
• Some feeding adaptations of predators are claws,
  teeth, fangs, stingers, and poison
• Prey display various defensive adaptations -
  hiding, fleeing, forming herds or schools,
  self-defense, coloration patterns, mimicry, and
  alarm calls

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Coloration Patterns and Mimicry
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Herbivory

• Herbivory (/ interaction) refers to an
  interaction in which an herbivore eats parts of a
  plant or alga
• It has led to evolution of plant mechanical and
  chemical defenses and adaptations by herbivores

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Fig. 54-6
A manatee is feeding on water hyacinth, an
introduced species, in Florida.
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Symbiosis

• Symbiosis is a relationship where two or more
  species live in direct and intimate contact with
  one another
• parasitism (/ interaction)
• mutualism (/ interaction), is an interspecific
  interaction that benefits both species
• A mutualism can be
• Obligate, where one species cannot survive
  without the other
• Facultative, where both species can survive alone
• commensalism (/0 interaction)

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Fig. 54-7
The tree and the ant are locked into relationship
where the survival of both partners depends on
the other. The ants provide the Acacia with
protection from herbivores and from competing
plants, while the tree provides the ants with
food and shelter. Facultative mutualism
(a) Acacia tree and ants (genus Pseudomyrmex)
(b) Area cleared by ants at the base of an acacia
tree
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Clownfish and Sea Anemones
Facultative Mutualism
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Fig. 54-8
Facultative Mutualism
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Parasitism
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Commensalism epiphytes
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protists in termite guts
Obligate Mutualism
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• In general, a few species in a community exert
  strong control on that communitys structure
• Two fundamental features of community structure
  are species diversity and feeding relationships

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Species Diversity

• Species diversity of a community is the variety
  of organisms that make up the community
• It has two components species richness and
  relative abundance
• 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

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Fig. 54-9
A
B
C
D
Community 1
Community 2
A 80 B 5 C 5 D 10
A 25 B 25 C 25 D 25
Two communities can have the same species
richness but a different relative abundance
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Trophic Structure

• Trophic structure is the feeding relationships
  between organisms in a community
• It is a key factor in community dynamics
• Food chains link trophic levels from producers to
  top carnivores

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Fig. 54-11
Quaternary consumers
Carnivore
Carnivore
Tertiary consumers
Carnivore
Carnivore
Secondary consumers
Carnivore
Carnivore
Primary consumers
Herbivore
Zooplankton
Primary producers
Plant
Phytoplankton
A terrestrial food chain
A marine food chain
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A food web is a branching food chain with complex
trophic interactions
Fig. 54-12
Humans
Smaller toothed whales
Baleen whales
Sperm whales
Elephant seals
Leopard seals
Crab-eater seals
Fishes
Squids
Birds
Carnivorous plankton
Copepods
Euphausids (krill)
Phyto- plankton
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Limits on Food Chain Length

• Two hypotheses attempt to explain food chain
  length
• The energetic hypothesis suggests that length is
  limited by inefficient energy transfer
• The dynamic stability hypothesis proposes that
  long food chains are less stable than short ones
• Most data support the energetic hypothesis

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Experimental data from the tree hole communities
showed that food chains were longest when food
supply (leaf litter) was greatest. Which
hypothesis about what ali its food chain length
do these results suggest?
energetic
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Fig. 54-14
5
4
3
Number of trophic links
2
1
0
High (control) natural rate of litter fall
Medium 1/10 natural rate
Low 1/100 natural rate
Productivity
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Species with a Large Impact

• Certain species have a very large impact on
  community structure
• Such species are highly abundant or play a
  pivotal role in community dynamics
• Dominant species are those that are most abundant
  or have the highest biomass (the total mass of
  all individuals in a population)

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Why are they dominant?

• One hypothesis suggests that dominant species are
  most competitive in exploiting resources
• Another hypothesis is that they are most
  successful at avoiding predators

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Invasive Species

• Species typically introduced to a new environment
  by humans, often lack predators or disease

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Kudzu

• Kudzu is a vine which was brought to North
  America from Asia in 1876 to help prevent soil
  erosion, which has since become an utter nuisance
  in some areas of the country. It can grow up to
  6.5 feet a week and its roots are nearly
  impossible to eradicate entirely.

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Other examples

• Dutch Elm Disease caused by a fungus and
  accidentally spread into the United States.
• Potato Blight caused by a fungus that caused
  the Great Potato Famine in Ireland in the 1840s.
  Spores have been carried all over the world.
• Small Pox spread of virus from Asia to all over
  the world.

Dutch Elm Disease
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• Dutch elm disease (DED) is caused by a member of
  the sac fungi (Ascomycota) affecting elm trees,
  and is spread by the elm bark beetle. Although
  believed to be originally native to Asia, the
  disease has been accidentally introduced into
  America and Europe, where it has devastated
  native populations of elms which had not had the
  opportunity to evolve resistance to the disease.
  The name "Dutch elm disease" refers to its
  identification in 1921 in the Netherlands by
  Dutch phytopathologists.

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Potato Blight caused by a fungus.
Smallpox caused by a virus.
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Keystone Species

• Keystone species exert strong control on a
  community by their ecological roles, or niches
• In contrast to dominant species, they are not
  necessarily abundant in a community

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Fig. 54-15
EXPERIMENT
Field studies of sea stars exhibit their role as
a keystone species in intertidal
communities They keep the number of mussels
controlled that outcompete other species.
RESULTS
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With Pisaster (control)
15
Number of species present
10
Without Pisaster (experimental)
5
0
1963
64
65
66
67
68
69
70
71
72
73
Year
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Fig. 54-16
100
80
Otter number ( max. count)
60
40
20
Observation of sea otter populations and their
predation shows how otters affect ocean
communities
Keystone species
0
(a) Sea otter abundance
400
After orcas entered the food chain and preyed
on the otters, notice the change in the sea
urchins and kelp.
300
Grams per 0.25 m2
200
100
0
(b) Sea urchin biomass
10
8
Number per 0.25 m2
6
4
2
0
1972
1985
1997
1989
1993
Year
(c) Total kelp density
Food chain
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This resulted in a loss of kelp forests.
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Ecological Succession

• Ecological succession is the sequence of
  community and ecosystem changes after a
  disturbance
• Primary succession occurs where no soil exists
  when succession begins
• Secondary succession begins in an area where soil
  remains after a disturbance

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Successive species can

• Inhibit growth of new organisms
• sphagnum moss making boggy areas
• in poorly drained sites
• Promote growth of new organisms
• Dryas and Alder trees raising N content
• Tolerate conditions that resulted from former
  species

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Fig. 54-22-4
Succession on the moraines in Glacier Bay,
Alaska, follows a predictable pattern of change
in vegetation and soil characteristics
1941
1907
Dryas stage
2
Pioneer stage, with fireweed dominant
1
5
10
15
0
Kilometers
1860
Glacier Bay
Alaska
1760
Alder stage
3
Spruce stage
4
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Succession at Mt. St. Helens in 1980
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• Pioneer stage first species
• Climax or dominant species stable, typically
  most biomass species

Mosses - pioneers
Hardwood Forests - dominant
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Fig. 54-23
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Succession is the result of changes induced by
the vegetation itself. On the glacial moraines,
vegetation lowers the soil pH and increases soil
nitrogen content.
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40
Soil nitrogen (g/m2)
30
20
10
0
Pioneer
Dryas
Alder
Spruce
Successional stage
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Dune Succession
Primary Succession
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Pond Succession
Secondary succession
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Human Disturbance

• Humans have the greatest impact on biological
  communities worldwide!
• Human disturbance to communities usually reduces
  species diversity
• Humans also prevent some naturally occurring
  disturbances, which can be important to community
  structure

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Fig. 54-24
Results from trawling.
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Biogeographic factors affect community
biodiversity

• Latitude and area are two key factors that affect
  a communitys species diversity
• - generally declines along an
  equatorial-polar gradient and is especially great
  in the tropics
• - two key factors are evolutionary history
  and climate
• The greater age of tropical environments may
  account for the greater species richness more
  growing time so more chance for evolutionary
  changes

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Area Effects

• The species-area curve quantifies the idea that,
  all other factors being equal, a larger
  geographic area has more species
• A species-area curve of North American breeding
  birds supports this idea

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Fig. 54-26
1,000
100
Number of species
10
1
0.1
1
10
100
103
104
105
106
107
108
109
1010
Area (hectares)
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Island Equilibrium Model

• Species richness on islands depends on island
  size, distance from the mainland, immigration,
  and extinction

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• The number of species found on an island can
  be determined by a balance between the
  immigration rate (or the movement of species onto
  the island from other islands) and the extinction
  rate (or the rate at which species already on the
  island become nonexistent). 

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Effect of Island Size
Immigration and extinction rates are affected by
the size of the island and its distance from a
non-island source of immigrant species
A larger island has higher species diversity for
two reasons it is a larger target, giving it a
greater probability of becoming the home to
immigrants, and it has a larger supply of
resources necessary to prevent extinctions. 
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Effect of Island Distance

• An island's distance from a mainland source of
  new immigrants, despite its size, is an important
  factor in species diversity. Even if two islands
  are the exact same size and all other factors are
  constant, the island closest to the mainland is
  more likely to attract a larger number of
  immigrant species due to its proximity and
  convenience

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Fig. 54-28
Studies of species richness on the Galápagos
Islands support the prediction that species
richness increases with island size
400
200
100
50
Number of plant species (log scale)
25
10
5
10
100
103
104
105
106
Area of island (hectares) (log scale)
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Community ecology is useful for understanding
pathogen life cycles and controlling human disease

• Ecological communities are universally affected
  by pathogens, which include disease-causing
  microorganisms, viruses, viroids (viral DNA), and
  prions (proteins)

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Pathogens can alter community structure quickly
and extensively
For example, coral reef communities are being
decimated by white-band disease
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• Human activities are transporting pathogens
  around the world at unprecedented rates
• Community ecology is needed to help study and
  combat them
• Zoonotic pathogens have been transferred from
  other animals to humans
• The transfer of pathogens can be direct or
  through an intermediate species called a vector
• Many of todays emerging human diseases are
  zoonotic SWINE FLU!

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Fig. 54-30

• Avian flu is a highly contagious virus of birds
• Ecologists are studying the potential spread of
  the virus from Asia to North America through
  migrating birds