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Community Ecology

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Title: Community Ecology


1
Community Ecology
Community Ecology
AP Chapter 54
  • AP Chapter 54

2
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.

3
What is a community?
  • A biological community is an assemblage of
    populations of various species living close
    enough for potential interaction

4
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)

5
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

6
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.

7
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
8
  • 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

9
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
10
  • 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.

11
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
12
  • 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
13
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

14
Coloration Patterns and Mimicry
15
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

16
Fig. 54-6
A manatee is feeding on water hyacinth, an
introduced species, in Florida.
17
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)

18
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
19
Clownfish and Sea Anemones
Facultative Mutualism
20
Fig. 54-8
Facultative Mutualism
21
Parasitism
22
Commensalism epiphytes
23
protists in termite guts
Obligate Mutualism
24
  • 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

25
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

26
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
27
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

28
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
29
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
30
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

31
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
32
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
33
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)

34
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

35
Invasive Species
  • Species typically introduced to a new environment
    by humans, often lack predators or disease

36
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.

37
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
38
  • 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.

39
Potato Blight caused by a fungus.
Smallpox caused by a virus.
40
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

41
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
20
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
42
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
43
This resulted in a loss of kelp forests.
44
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

45
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46
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

47
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
48
Succession at Mt. St. Helens in 1980
49
  • Pioneer stage first species
  • Climax or dominant species stable, typically
    most biomass species

Mosses - pioneers
Hardwood Forests - dominant
50
Fig. 54-23
60
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.
50
40
Soil nitrogen (g/m2)
30
20
10
0
Pioneer
Dryas
Alder
Spruce
Successional stage
51
Dune Succession
Primary Succession
52
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53
Pond Succession
Secondary succession
54
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

55
Fig. 54-24
Results from trawling.
56
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

57
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

58
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)
59
Island Equilibrium Model
  • Species richness on islands depends on island
    size, distance from the mainland, immigration,
    and extinction

60
  • 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). 

61
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. 
62
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

63
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)
64
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)

65
Pathogens can alter community structure quickly
and extensively
For example, coral reef communities are being
decimated by white-band disease
66
  • 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!

67
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
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