AP Biology

1
AP Biology

• Ecology Unit
• Chapters 52-54

2
Chapter 52

• Ecology is the scientific study of the
  interactions between organisms and the
  environment
• These interactions determine distribution of
  organisms and their abundance
• Ecology reveals the richness of the biosphere

3
The Scope of Ecological Research

• Ecologists work at levels ranging from individual
  organisms to the planet

• 1-Organismal ecology studies how an organisms
  structure, physiology, and (for animals) behavior
  meet environmental challenges
• 2-Population ecology focuses on factors affecting
  how many individuals of a species live in an area
• A population is a group of individuals of the
  same species living in an area
• 3-Community ecology deals with the whole array of
  interacting species in a community
• A community is a group of populations of
  different species in an area
• 4-Ecosystem ecology emphasizes energy flow and
  chemical cycling among the various biotic and
  abiotic components
• An ecosystem is the community of organisms in an
  area and the physical factors with which they
  interact

4

• 5-Landscape ecology deals with arrays of
  ecosystems and how they are arranged in a
  geographic region
• A landscape is a mosaic of connected ecosystems
• 6-The biosphere is the global ecosystem, the sum
  of all the planets ecosystems
• Global ecology examines the influence of energy
  and materials on organisms across the biosphere

5
Concept 52.2 Interactions between organisms and
the environment limit the distribution of species

• Ecologists have long recognized global and
  regional patterns of distribution of organisms
  within the biosphere
• Biogeography is a good starting point for
  understanding what limits geographic distribution
  of species
• Ecologists recognize two kinds of factors that
  determine distribution biotic, or living
  factors, and abiotic, or nonliving factors

6
Fig. 52-6
Ecologists consider multiple factors when
attempting to explain the distribution of species
Why is species X absent from an area?
Area inaccessible or insufficient time
Yes
Yes
Does dispersal limit its distribution?
Habitat selection
Yes
Predation, parasitism, competition, disease
Chemical factors
Does behavior limit its distribution?
No
Do biotic factors (other species) limit
its distribution?
Water Oxygen Salinity pH Soil nutrients, etc.
No
Do abiotic factors limit its distribution?
No
Temperature Light Soil structure Fire Moisture,
etc.
Physical factors
Flowchart of factors limiting geographic
distribution
7
Dispersal and Distribution

• Dispersal is movement of individuals away from
  centers of high population density or from their
  area of origin
• Dispersal contributes to global distribution of
  organisms

8
Species Transplants

• Species transplants include organisms that are
  intentionally or accidentally relocated from
  their original distribution
• Species transplants can disrupt the communities
  or ecosystems to which they have been introduced

9
Fig. 52-8
RESULTS
100
Both limpets and urchins removed
80
Sea urchin
Only urchins removed
60
Seaweed cover ()
Limpet
40
Only limpets removed
20
Control (both urchins and limpets present)
0
August 1982
August 1983
February 1983
February 1984
10
Climate

• Four major abiotic components of climate are
  temperature, water, sunlight, and wind
• The long-term prevailing weather conditions in an
  area constitute its climate
• Macroclimate consists of patterns on the global,
  regional, and local level
• Microclimate consists of very fine patterns, such
  as those encountered by the community of
  organisms underneath a fallen log

11
Fig. 52-10c
60ºN
30ºN
March equinox
0º (equator)
June solstice
30ºS
December solstice
Constant tilt of 23.5º
September equinox
Seasonal variations of light and temperature
increase steadily toward the poles
12

• Seasonality
• The angle of the sun leads to many seasonal
  changes in local environments
• Lakes are sensitive to seasonal temperature
  change and experience seasonal turnover

13
Concept 52.3 Aquatic biomes are diverse and
dynamic systems that cover most of Earth

• Biomes are the major ecological associations that
  occupy broad geographic regions of land or water
• Varying combinations of biotic and abiotic
  factors determine the nature of biomes

14

• Aquatic biomes account for the largest part of
  the biosphere in terms of area
• They can contain fresh water or salt water
  (marine)
• Oceans cover about 75 of Earths surface and
  have an enormous impact on the biosphere

15
Fig. 52-16
Stratification of Aquatic Biomes
Intertidal zone
Oceanic zone
Neritic zone
Littoral zone
Limnetic zone
0
Photic zone
200 m
Continental shelf
Pelagic zone
Benthic zone
Aphotic zone
Photic zone
Pelagic zone
Benthic zone
Aphotic zone
2,0006,000 m
Abyssal zone
(a) Zonation in a lake
(b) Marine zonation
Many aquatic biomes are stratified into zones or
layers defined by light penetration, temperature,
and depth
16

• In oceans and most lakes, a temperature boundary
  called the thermocline separates the warm upper
  layer from the cold deeper water
• Many lakes undergo a semiannual mixing of their
  waters called turnover
• Turnover mixes oxygenated water from the surface
  with nutrient-rich water from the bottom

17
Fig. 52-17-5
Summer
Winter
Spring
Autumn
4º
22º
4º
0º
20º
4º
4º
2º
18º
4º
4º
4º
8º
4º
4º
4º
6º
4º
4º
4º
5º
4ºC
4ºC
4ºC
4ºC
Thermocline
18

• Lakes
• Oligotrophic lakes are nutrient-poor and
  generally oxygen-rich
• Eutrophic lakes are nutrient-rich and often
  depleted of oxygen if ice covered in winter
• Rooted and floating aquatic plants live in the
  shallow and well-lighted littoral zone
• Water is too deep in the limnetic zone to support
  rooted aquatic plants small drifting animals
  called zooplankton graze on the phytoplankton

19

• Wetlands
• A wetland is a habitat that is inundated by water
  at least some of the time and that supports
  plants adapted to water-saturated soil
• Wetlands can develop in shallow basins, along
  flooded river banks, or on the coasts of large
  lakes and seas
• Wetlands are among the most productive biomes on
  earth and are home to diverse invertebrates and
  birds

20

• Streams and Rivers
• The most prominent physical characteristic of
  streams and rivers is current
• A diversity of fishes and invertebrates inhabit
  unpolluted rivers and streams
• Damming and flood control impair natural
  functioning of stream and river ecosystems

21

• Estuaries
• An estuary is a transition area between river and
  sea
• Salinity varies with the rise and fall of the
  tides
• Estuaries are nutrient rich and highly productive
• An abundant supply of food attracts marine
  invertebrates and fish

Video Flapping Geese
22

• Oceanic Pelagic Zone
• The oceanic pelagic biome is a vast realm of open
  blue water, constantly mixed by wind-driven
  oceanic currents
• This biome covers approximately 70 of Earths
  surface
• Phytoplankton and zooplankton are the dominant
  organisms in this biome also found are
  free-swimming animals

Video Shark Eating a Seal
23

• Coral Reefs
• Coral reefs are formed from the calcium carbonate
  skeletons of corals (phylum Cnidaria)
• Corals require a solid substrate for attachment
• Unicellular algae live within the tissues of the
  corals and form a mutualistic relationship that
  provides the corals with organic molecules

Video Coral Reef
Video Clownfish and Anemone
24
Concept 52.4 The structure and distribution of
terrestrial biomes are controlled by climate and
disturbance

• Climate is very important in determining why
  terrestrial biomes are found in certain areas
• Biome patterns can be modified by disturbance
  such as a storm, fire, or human activity

25
Fig. 52-19
Tropical forest
Savanna
Desert
Chaparral
30ºN
Temperate grassland
Tropic of Cancer
Equator
Temperate broadleaf forest
Tropic of Capricorn
Northern coniferous forest
30ºS
Tundra
High mountains
Polar ice
26
General Features of Terrestrial Biomes and the
Role of Disturbance

• Terrestrial biomes are often named for major
  physical or climatic factors and for vegetation
• Terrestrial biomes usually grade into each other,
  without sharp boundaries
• The area of intergradation, called an ecotone,
  may be wide or narrow

27

• Vertical layering is an important feature of
  terrestrial biomes, and in a forest it might
  consist of an upper canopy, low-tree layer, shrub
  understory, ground layer of herbaceous plants,
  forest floor, and root layer
• Layering of vegetation in all biomes provides
  diverse habitats for animals
• Biomes are dynamic and usually exhibit extensive
  patchiness

28

• Terrestrial Biomes
• Terrestrial biomes can be characterized by
  distribution, precipitation, temperature, plants,
  and animals

29

• Tropical Forest
• In tropical rain forests, rainfall is relatively
  constant, while in tropical dry forests
  precipitation is highly seasonal
• Tropical forests are vertically layered and
  competition for light is intense
• Tropical forests are home to millions of animal
  species, including an estimated 530 million
  still undescribed species of insects, spiders,
  and other arthropods

30

• Desert
• Precipitation is low and highly variable,
  generally less than 30 cm per year deserts may
  be hot or cold
• Desert plants are adapted for heat and
  desiccation tolerance, water storage, and reduced
  leaf surface area
• Common desert animals include many kinds of
  snakes and lizards, scorpions, ants, beetles,
  migratory and resident birds, and seed-eating
  rodents many are nocturnal

31

• Savanna
• Savanna precipitation and temperature are
  seasonal
• Grasses and forbs make up most of the ground
  cover
• Common inhabitants include insects and mammals
  such as wildebeests, zebras, lions, and hyenas

32

• Chaparral
• Chaparral climate is highly seasonal, with cool
  and rainy winters and hot dry summers
• The chaparral is dominated by shrubs, small
  trees, grasses, and herbs many plants are
  adapted to fire and drought
• Animals include amphibians, birds and other
  reptiles, insects, small mammals and browsing
  mammals

33
Fig. 52-21d
An area of chaparral in California
34

• Northern Coniferous Forest
• The northern coniferous forest, or taiga, extends
  across northern North America and Eurasia and is
  the largest terrestrial biome on Earth
• Winters are cold and long while summers may be
  hot
• The conical shape of conifers prevents too much
  snow from accumulating and breaking their
  branches
• Animals include migratory and resident birds, and
  large mammals

35

• Temperate Broadleaf Forest
• Winters are cool, while summers are hot and
  humid significant precipitation falls year round
  as rain and snow
• A mature temperate broadleaf forest has vertical
  layers dominated by deciduous trees in the
  Northern Hemisphere and evergreen eucalyptus in
  Australia
• Mammals, birds, and insects make use of all
  vertical layers in the forest
• In the Northern Hemisphere, many mammals
  hibernate in the winter

36

• Tundra
• Tundra covers expansive areas of the Arctic
  alpine tundra exists on high mountaintops at all
  latitudes
• Winters are long and cold while summers are
  relatively cool precipitation varies
• Permafrost, a permanently frozen layer of soil,
  prevents water infiltration
• Vegetation is herbaceous (mosses, grasses, forbs,
  dwarf shrubs and trees, and lichen) and supports
  birds, grazers, and their predators

37
Fig. 52-21h
Denali National Park, Alaska, in autumn
38
Fig. 52-UN1
Why is species X absent from an area?
Yes
Area inaccessible or insufficient time
Does dispersal limit its distribution?
No
Yes
Does behavior limit its distribution?
Habitat selection
No
Yes
Do biotic factors (other species) limit its
distribution?
Predation, parasitism, competition, disease
No
Chemical factors
Water, oxygen, salinity, pH, soil nutrients, etc.
Do abiotic factors limit its distribution?
Temperature, light, soil structure, fire,
moisture, etc.
Physical factors
39
Fig. 52-T1
40
Fig. 52-UN3
41
Fig. 52-UN2
100
Mean height (cm)
50
0
3,000
2,000
Altitude (m)
Sierra Nevada
Great Basin Plateau
1,000
0
Seed collection sites
42
Chapter 53
Population ecology is the study of populations in
relation to environment, including environmental
influences on density and distribution, age
structure, and population size
43
Concept 53.1 Dynamic biological processes
influence population density, dispersion, and
demographics

• A population is a group of individuals of a
  single species living in the same general area
• Density is the number of individuals per unit
  area or volume
• Dispersion is the pattern of spacing among
  individuals within the boundaries of the
  population

44

• Density is the result of an interplay between
  processes that add individuals to a population
  and those that remove individuals
• Immigration is the influx of new individuals from
  other areas
• Emigration is the movement of individuals out of
  a population

45
Fig. 53-3
Births
Deaths
Births and immigration add individuals to a
population.
Deaths and emigration remove individuals from a
population.
Immigration
Emigration
46
Patterns of Dispersion

• Environmental and social factors influence
  spacing of individuals in a population
• Three types of Dispersion
• Clumping is most common, individuals aggregate in
  patches, may be influenced by resource
  availability and behavior
• Uniform is one in which individuals are evenly
  distributed, may be influenced by social
  interactions such as territoriality
• Random is the position of each individual is
  independent of other individuals, it occurs in
  the absence of strong attractions or repulsions

47
Fig. 53-4
(a) Clumped
(b) Uniform
(c) Random
48
Demographics

• Demography is the study of the vital statistics
  of a population and how they change over time
• Death rates and birth rates are of particular
  interest to demographers
• A life table is an age-specific summary of the
  survival pattern of a population
• It is best made by following the fate of a
  cohort, a group of individuals of the same age
• The life table of Beldings ground squirrels
  reveals many things about this population

49
Table 53-1
50
Survivorship Curves

• A survivorship curve is a graphic way of
  representing the data in a life table
• The survivorship curve for Beldings ground
  squirrels shows a relatively constant death rate

51
Fig. 53-5
1,000
100
Number of survivors (log scale)
Females
10
Males
1
2
0
4
8
6
10
Age (years)
52

• Survivorship curves can be classified into three
  general types
• Type I low death rates during early and middle
  life, then an increase among older age groups
• Type II the death rate is constant over the
  organisms life span
• Type III high death rates for the young, then a
  slower death rate for survivors

53
Fig. 53-6
1,000
I
100
II
Number of survivors (log scale)
10
III
1
0
50
100
Percentage of maximum life span
54
Reproductive Rates

• For species with sexual reproduction,
  demographers often concentrate on females in a
  population
• A reproductive table, or fertility schedule, is
  an age-specific summary of the reproductive rates
  in a population
• It describes reproductive patterns of a population

55
Table 53-2
56
Concept 53.2 Life history traits are products of
natural selection

• An organisms life history comprises the traits
  that affect its schedule of reproduction and
  survival
• The age at which reproduction begins
• How often the organism reproduces
• How many offspring are produced during each
  reproductive cycle
• Life history traits are evolutionary outcomes
  reflected in the development, physiology, and
  behavior of an organism

57
Evolution and Life History Diversity

• Life histories are very diverse
• Species that exhibit semelparity, or big-bang
  reproduction, reproduce once and die
• Species that exhibit iteroparity, or repeated
  reproduction, produce offspring repeatedly
• Highly variable or unpredictable environments
  likely favor big-bang reproduction, while
  dependable environments may favor repeated
  reproduction

58
Fig. 53-7
59
Trade-offs and Life Histories

• Organisms have finite resources, which may lead
  to trade-offs between survival and reproduction
• In animals, parental care of smaller broods may
  facilitate survival of offspring

60
Fig. 53-8
RESULTS
100
Male
Female
80
60
Parents surviving the following winter ()
40
20
0
Reduced brood size
Normal brood size
Enlarged brood size
61

• Some plants produce a large number of small
  seeds, ensuring that at least some of them will
  grow and eventually reproduce
• Other types of plants produce a moderate number
  of large seeds that provide a large store of
  energy that will help seedlings become established

62
Fig. 53-9
(a) Dandelion
(b) Coconut palm
63
Concept 53.3 The exponential model describes
population growth in an idealized, unlimited
environment

• It is useful to study population growth in an
  idealized situation
• Idealized situations help us understand the
  capacity of species to increase and the
  conditions that may facilitate this growth

64
Per Capita Rate of Increase

• If immigration and emigration are ignored, a
  populations growth rate (per capita increase)
  equals birth rate minus death rate

65

• Zero population growth occurs when the birth rate
  equals the death rate
• Most ecologists use differential calculus to
  express population growth as growth rate at a
  particular instant in time

where N population size, t time, and r per
capita rate of increase birth death
66
Exponential Growth

• Exponential population growth is population
  increase under idealized conditions
• Under these conditions, the rate of reproduction
  is at its maximum, called the intrinsic rate of
  increase
• Equation of exponential population growth

67
Exponential population growth results in a
J-shaped curve

• The J-shaped curve of exponential growth
  characterizes some rebounding populations

68
Fig. 53-10
2,000
dN
1.0N

dt
1,500
dN
0.5N

dt
Population size (N)
1,000
500
0
0
5
10
15
Number of generations
69
Concept 53.4 The logistic model describes how a
population grows more slowly as it nears its
carrying capacity

• Exponential growth cannot be sustained for long
  in any population
• A more realistic population model limits growth
  by incorporating carrying capacity
• Carrying capacity (K) is the maximum population
  size the environment can support
• In the logistic population growth model, the per
  capita rate of increase declines as carrying
  capacity is reached
• The logistic model of population growth produces
  a sigmoid (S-shaped) curve

70
Fig. 53-12
Exponential growth
2,000
dN
1.0N

dt
1,500
K 1,500
Population size (N)
Logistic growth
1,000
1,500 N
dN
1.0N

1,500
dt
500
0
0
5
10
15
Number of generations
71
The Logistic Model and Real Populations

• The growth of laboratory populations of paramecia
  fits an S-shaped curve
• These organisms are grown in a constant
  environment lacking predators and competitors

72
Fig. 53-13a
1,000
800
Number of Paramecium/mL
600
400
200
0
0
5
10
15
Time (days)
(a) A Paramecium population in the lab
73
The Logistic Model and Life Histories

• Life history traits favored by natural selection
  may vary with population density and
  environmental conditions
• K-selection, or density-dependent selection,
  selects for life history traits that are
  sensitive to population density
• r-selection, or density-independent selection,
  selects for life history traits that maximize
  reproduction

74
Population Change and Population Density

• In density-independent populations, birth rate
  and death rate do not change with population
  density
• In density-dependent populations, birth rates
  fall and death rates rise with population density

75
Density-Dependent Population Regulation

• Density-dependent birth and death rates are an
  example of negative feedback that regulates
  population growth
• They are affected by many factors, such as
  competition for resources, territoriality,
  disease, predation, toxic wastes, and intrinsic
  factors

76
Competition for Resources

• In crowded populations, increasing population
  density intensifies competition for resources and
  results in a lower birth rate

77
Territoriality

• In many vertebrates and some invertebrates,
  competition for territory may limit density
• Cheetahs are highly territorial, using chemical
  communication to warn other cheetahs of their
  boundaries
• Oceanic birds exhibit territoriality in nesting
  behavior

78
Fig. 53-17
(a) Cheetah marking its territory
(b) Gannets
79
Disease

• Population density can influence the health and
  survival of organisms
• In dense populations, pathogens can spread more
  rapidly

80
Predation

• As a prey population builds up, predators may
  feed preferentially on that species

81
Toxic Wastes

• Accumulation of toxic wastes can contribute to
  density-dependent regulation of population size

82
Intrinsic Factors

• For some populations, intrinsic (physiological)
  factors appear to regulate population size

83
Population Dynamics

• The study of population dynamics focuses on the
  complex interactions between biotic and abiotic
  factors that cause variation in population size
• Stability and Fluctuation
• Long-term population studies have challenged the
  hypothesis that populations of large mammals are
  relatively stable over time
• Weather can affect population size over time
• Changes in predation pressure can drive
  population fluctuations-Next slide

84
Fig. 53-19
2,500
50
Wolves
Moose
2,000
40
1,500
30
Number of moose
Number of wolves
1,000
20
500
10
0
0
1955
1965
1975
1985
1995
2005
Year
85
Concept 53.6 The human population is no longer
growing exponentially but is still increasing
rapidly

• No population can grow indefinitely, and humans
  are no exception
• Though the global population is still growing,
  the rate of growth began to slow during the 1960s

86
Regional Patterns of Population Change

• To maintain population stability, a regional
  human population can exist in one of two
  configurations
• Zero population growth High birth rate High
  death rate
• Zero population growth Low birth rate Low
  death rate
• The demographic transition is the move from the
  first state toward the second state

87
Fig. 53-24
50
40
30
Birth or death rate per 1,000 people
20
10
Sweden
Mexico
Birth rate
Birth rate
Death rate
Death rate
0
1750
1800
1900
1950
2000
2050
1850
Year
88

• The demographic transition is associated with an
  increase in the quality of health care and
  improved access to education, especially for
  women
• Most of the current global population growth is
  concentrated in developing countries

89
Age Structure

• One important demographic factor in present and
  future growth trends is a countrys age structure
• Age structure is the relative number of
  individuals at each age
• Age structure diagrams can predict a populations
  growth trends
• They can illuminate social conditions and help us
  plan for the future

90
Fig. 53-25
Rapid growth
Slow growth
No growth
Afghanistan
United States
Italy
Male
Female
Age
Age
Male
Female
Male
Female
85
85
8084
8084
7579
7579
7074
7074
6569
6569
6064
6064
5559
5559
5054
5054
4549
4549
4044
4044
3539
3539
3034
3034
2529
2529
2024
2024
1519
1519
1014
1014
59
59
04
04
10 
10 
8
8
6
6
4
4
2
2
0
6
6
4
4
2
2
0
8
8
6
6
4
4
2
2
0
8
8
Percent of population
Percent of population
Percent of population
91
Limits on Human Population Size

• The ecological footprint concept summarizes the
  aggregate land and water area needed to sustain
  the people of a nation
• It is one measure of how close we are to the
  carrying capacity of Earth
• Countries vary greatly in footprint size and
  available ecological capacity

92

• The carrying capacity of Earth for humans is
  uncertain
• The average estimate is 1015 billion
• Our carrying capacity could potentially be
  limited by food, space, nonrenewable resources,
  or buildup of wastes

93
Chapter 54

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

94
Concept 54.1 Community interactions are
classified by whether they help, harm, or have no
effect on the species involved

• Ecologists call 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)

95
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 competitive exclusion principle states that
  two species competing for the same limiting
  resources cannot coexist in the same place

96
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
• Ecologically similar species can coexist in a
  community if there are one or more significant
  differences in their niches

97

• Resource partitioning is differentiation of
  ecological niches, enabling similar species to
  coexist in a community

98
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
99

• As a result of competition, a species
  fundamental niche may differ from its realized
  niche

100
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
101
Character Displacement

• Character displacement is a tendency for
  characteristics to be more divergent in sympatric
  populations of two species than in allopatric
  populations of the same two species
• An example is variation in beak size between
  populations of two species of Galápagos finches

102
Fig. 54-4
G. fuliginosa
G. fortis
Beak depth
Los Hermanos
60
40
G. fuliginosa, allopatric
20
0
Daphne
60
40
Percentages of individuals in each size class
G. fortis, allopatric
20
0
Sympatric populations
Santa María, San Cristóbal
60
40
20
0
8
10
12
14
16
Beak depth (mm)
103
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

104

• Prey display various defensive adaptations
• Behavioral defenses include hiding, fleeing,
  forming herds or schools, self-defense, and alarm
  calls
• Animals also have morphological and physiological
  defense adaptations
• Cryptic coloration, or camouflage, makes prey
  difficult to spot

Video Seahorse Camouflage
105
Fig. 54-5
(a)
Cryptic coloration
Canyon tree frog

(b)
Aposematic coloration
Poison dart frog

(c) Batesian mimicry A harmless species mimics a
harmful one.
Hawkmoth larva

Müllerian mimicry Two unpalatable species mimic
each other.
(d)
Cuckoo bee

Green parrot snake

Yellow jacket

106

• Animals with effective chemical defense often
  exhibit bright warning coloration, called
  aposematic coloration
• Predators are particularly cautious in dealing
  with prey that display such coloration

107

• In some cases, a prey species may gain
  significant protection by mimicking the
  appearance of another species
• In Batesian mimicry, a palatable or harmless
  species mimics an unpalatable or harmful model

108

• In Müllerian mimicry, two or more unpalatable
  species resemble each other

109
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

110
Symbiosis

• Symbiosis is a relationship where two or more
  species live in direct and intimate contact with
  one another

111
Parasitism

• In parasitism (/ interaction), one organism,
  the parasite, derives nourishment from another
  organism, its host, which is harmed in the
  process
• Parasites that live within the body of their host
  are called endoparasites parasites that live on
  the external surface of a host are ectoparasites

112
Mutualism

• Mutualistic symbiosis, or 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

Video Clownfish and Anemone
113
Commensalism

• In commensalism (/0 interaction), one species
  benefits and the other is apparently unaffected
• Commensal interactions are hard to document in
  nature because any close association likely
  affects both species

114
Concept 54.2 Dominant and keystone species exert
strong controls on community structure

• 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

115
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

Video Shark Eating a Seal
116
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
117
Food Webs

• A food web is a branching food chain with complex
  trophic interactions
• Species may play a role at more than one trophic
  level
• Food webs can be simplified by isolating a
  portion of a community that interacts very little
  with the rest of the community

118
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
119
Limits on Food Chain Length

• Each food chain in a food web is usually only a
  few links long
• Two hypotheses attempt to explain food chain
  length the energetic hypothesis and the dynamic
  stability hypothesis

120

• 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

121
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

122
Dominant Species

• Dominant species are those that are most abundant
  or have the highest biomass
• Biomass is the total mass of all individuals in a
  population
• Dominant species exert powerful control over the
  occurrence and distribution of other species

123

• One hypothesis suggests that dominant species are
  most competitive in exploiting resources
• Another hypothesis is that they are most
  successful at avoiding predators
• Invasive species, typically introduced to a new
  environment by humans, often lack predators or
  disease

124
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

125
Foundation Species (Ecosystem Engineers)

• Foundation species (ecosystem engineers) cause
  physical changes in the environment that affect
  community structure
• For example, beaver dams can transform landscapes
  on a very large scale
• Some foundation species act as facilitators that
  have positive effects on survival and
  reproduction of some other species in the
  community

126
Concept 54.3 Disturbance influences species
diversity and composition

• Decades ago, most ecologists favored the view
  that communities are in a state of equilibrium
• This view was supported by F. E. Clements who
  suggested that species in a climax community
  function as a superorganism

127

• Other ecologists, including A. G. Tansley and
  H. A. Gleason, challenged whether communities
  were at equilibrium
• Recent evidence of change has led to a
  nonequilibrium model, which describes communities
  as constantly changing after being buffeted by
  disturbances

128
Characterizing Disturbance

• A disturbance is an event that changes a
  community, removes organisms from it, and alters
  resource availability
• Fire is a significant disturbance in most
  terrestrial ecosystems
• It is often a necessity in some communities

129

• The large-scale fire in Yellowstone National Park
  in 1988 demonstrated that communities can often
  respond very rapidly to a massive disturbance

130
Fig. 54-21
(a) Soon after fire
(b) One year after fire
131
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

132

• Early-arriving species and later-arriving species
  may be linked in one of three processes
• Early arrivals may facilitate appearance of later
  species by making the environment favorable
• They may inhibit establishment of later species
• They may tolerate later species but have no
  impact on their establishment

133

• Retreating glaciers provide a valuable
  field-research opportunity for observing
  succession
• Succession on the moraines in Glacier Bay,
  Alaska, follows a predictable pattern of change
  in vegetation and soil characteristics

134
Fig. 54-22-1
1941
1907
Pioneer stage, with fireweed dominant
1
5
10
15
0
Kilometers
1860
Glacier Bay
Alaska
1760
135
Fig. 54-22-2
1941
1907
Dryas stage
2
Pioneer stage, with fireweed dominant
1
5
10
15
0
Kilometers
1860
Glacier Bay
Alaska
1760
136
Fig. 54-22-3
1941
1907
Dryas stage
2
Pioneer stage, with fireweed dominant
1
5
10
15
0
Kilometers
1860
Glacier Bay
Alaska
1760
Alder stage
3
137
Fig. 54-22-4
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
138
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

139
Concept 54.4 Biogeographic factors affect
community biodiversity

• Latitude and area are two key factors that affect
  a communitys species diversity

140
Latitudinal Gradients

• Species richness generally declines along an
  equatorial-polar gradient and is especially great
  in the tropics
• Two key factors in equatorial-polar gradients of
  species richness are probably evolutionary
  history and climate
• The greater age of tropical environments may
  account for the greater species richness

141

• Climate is likely the primary cause of the
  latitudinal gradient in biodiversity
• Two main climatic factors correlated with
  biodiversity are solar energy and water
  availability
• They can be considered together by measuring a
  communitys rate of evapotranspiration
• Evapotranspiration is evaporation of water from
  soil plus transpiration of water from plants

142
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

143
Island Equilibrium Model

• Species richness on islands depends on island
  size, distance from the mainland, immigration,
  and extinction
• The equilibrium model of island biogeography
  maintains that species richness on an ecological
  island levels off at a dynamic equilibrium point

144

• Studies of species richness on the Galápagos
  Islands support the prediction that species
  richness increases with island size

145
Concept 54.5 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, and prions
• Pathogens can alter community structure quickly
  and extensively

146
Pathogens and Community Structure

• Pathogens can have dramatic effects on
  communities
• Human activities are transporting pathogens
  around the world at unprecedented rates
• Community ecology is needed to help study and
  combat them

147
Community Ecology and Zoonotic Diseases

• 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

148
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