Ecosystems

1
Ecosystems

• Chapter 26

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LEARNING OBJECTIVE 1

• Define ecology
• Distinguish among population, community,
  ecosystem, and biosphere

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KEY TERMS

• ECOLOGY
• Discipline of biology that studies interrelations
  between living things and their environments
• Ecologists study populations, communities,
  ecosystems, and the biosphere

4
KEY TERMS

• POPULATION
• A group of organisms of the same species that
  live in a defined geographic area at the same
  time
• COMMUNITY
• An association of populations of different
  species living in a defined habitat with some
  degree of interdependence

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Community A Nurse Log
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KEY TERMS

• ECOSYSTEM
• Interacting system that encompasses a community
  and its nonliving, physical environment
• BIOSPHERE
• All of Earths living organisms, collectively

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LEARNING OBJECTIVE 2

• Explain the difference between J-shaped and
  S-shaped population growth curves

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Dispersion in Populations
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(c) Uniform dispersion
(b) Clumped dispersion
(a) Random dispersion
Fig. 26-2, p. 517
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Intrinsic Rate of Increase

• The maximum rate at which a population could
  increase in number under ideal conditions

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Exponential Population Growth

• J-shaped curve
• An accelerated pattern of growth exhibited by
  certain populations for a limited period

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Exponential Population Growth
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Logistic Population Growth

• S-shaped curve
• After accelerated growth, growth rate decreases
• Natural populations seldom follow the logistic
  growth curve closely

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Logistic Population Growth and Carrying Capacity
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LEARNING OBJECTIVE 3

• Summarize the three main types of survivorship
  curves

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Survivorship

• The probability that a given individual in a
  population will survive to a particular age

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3 General Survivorship Curves

• Type I survivorship
• Mortality greatest in old age
• Type II survivorship
• Mortality spread evenly across all age groups
• Type III survivorship
• Mortality greatest among the young

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Survivorship Curves
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Experiment Drummond Phlox
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Metapopulation
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LEARNING OBJECTIVE 4

• Characterize producers, consumers, and decomposers

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KEY TERMS

• PRODUCER
• An organism that synthesizes organic compounds
  from simple inorganic raw materials

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KEY TERMS

• CONSUMER
• An organism that cannot synthesize its own food
  from inorganic raw materials
• Must obtain energy and body-building materials
  from other organisms

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KEY TERMS

• DECOMPOSER
• A microorganism that breaks down dead organic
  material and uses the decomposition products as a
  source of energy

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LEARNING OBJECTIVE 5

• Describe what is meant by an organisms
  ecological niche

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KEY TERMS

• ECOLOGICAL NICHE
• The totality of an organisms adaptations, its
  use of resources, its interactions with other
  organisms, and the lifestyle to which it is
  fitted in its community

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LEARNING OBJECTIVE 6

• Define competition, predation, and symbiosis
• Distinguish among mutualism, commensalism, and
  parasitism

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KEY TERMS

• COMPETITION
• Interaction among two or more individuals that
  attempt to use the same essential resource, such
  as food, water, sunlight, or living space

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KEY TERMS

• PREDATION
• A relationship in which one organism (the
  predator) kills and devours another organism (the
  prey)

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KEY TERMS

• SYMBIOSIS
• An intimate relationship between two or more
  organisms of different species
• Symbiosis includes mutualism, commensalism, and
  parasitism

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Symbiosis

• Mutualism
• Both partners benefit
• Commensalism
• One organism benefits
• Other is unaffected
• Parasitism
• One organism (the parasite) benefits
• Other (the host) is harmed

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Plant Defense Against Herbivores
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Mutualism
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Commensalism
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LEARNING OBJECTIVE 7

• Define ecological succession
• Distinguish between primary succession and
  secondary succession

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KEY TERMS

• ECOLOGICAL SUCCESSION
• Sequence of changes in the species composition of
  a community over time

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Succession

• Primary succession begins in an area not
  previously inhabited
• Example bare rock
• Secondary succession begins in an area where
  there was a preexisting community and a
  well-formed soil
• Example abandoned farmland

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Primary Succession
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Lichens and mosses
Exposed rocks
Balsam fir, paper birch, and white spruce forest
community
Jack pine, black spruce, and aspen
Low shrubs
Ferns, grasses, and herbs
Time
Fig. 26-12, p. 526
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Secondary Succession
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LEARNING OBJECTIVE 8

• Summarize the concept of energy flow through a
  food web

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KEY TERMS

• TROPHIC LEVEL
• Each sequential step in a food chain or food web,
  from producer to primary, secondary, or tertiary
  consumers

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Energy Flow

• Energy flows through an ecosystem in one
  direction, from sun to producer to consumer to
  decomposer
• Energy used for metabolic purposes at a given
  trophic level is unavailable to the next trophic
  level

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Solar Energy
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Less than one-billionth of the suns total
energy reaches Earths outer atmosphere.
30 reflected back into space immediately
47 absorbed by the atmosphere
Less than 1 drives the winds and ocean currents
All solar energy is ultimately reradiated to
space as heat
0.02 captured by photosynthesis
Fig. 26-14, p. 528
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Trophic Levels
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Fourth trophic level tertiary consumers
Third trophic level secondary consumers
Second trophic level primary consumers
First tropic level producers
Decomposers (saprotrophs)
Energy from sun
Heat
Heat
Heat
Heat
Heat
Fig. 26-15, p. 529
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Stepped Art
Fig. 26-15, p. 529
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A Food Web
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Energy Pyramid
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Tertiary consumers (21)
Decomposers (5060)
Secondary consumers (383)
Primary consumers (3368)
Producers (20,810)
Fig. 26-17, p. 531
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LEARNING OBJECTIVE 9

• Describe the main steps in the carbon, nitrogen,
  and hydrologic cycles

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KEY TERMS

• BIOGEOCHEMICAL CYCLE
• Process by which matter cycles from the living
  world to the nonliving, physical environment and
  back again

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The Carbon Cycle

• Carbon dioxide gas (CO2) enters plants, algae,
  and cyanobacteria
• Which incorporate it into organic molecules
  through photosynthesis
• Cellular respiration, combustion, erosion of
  limestone return CO2 to water and atmosphere
• Making it available to producers again

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Carbon Cycle
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Air (CO2)
2
Soil microorganism respiration
1
2
2
Animal and plant respiration
Decomposition
Photosynthesis by land plants
5
Combustion (human and natural)
6
Dissolved CO2 in water
Erosion of limestone to form dissolved CO2
Marine plankton remains
Shells of marine organisms burial and
compaction to form rock (limestone)
Soil
Coal
Partly decomposed plant remains
4
Natural gas
3
7
Coal
Oil
Fig. 26-18, p. 531
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The Nitrogen Cycle

• 1. Nitrogen fixation
• Conversion of nitrogen gas to ammonia
• 2. Nitrification
• Conversion of ammonia or ammonium to nitrate
• 3. Assimilation
• Conversion of nitrates, ammonia, or ammonium to
  proteins, chlorophyll, and other
  nitrogen-containing compounds by plants

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The Nitrogen Cycle

• 4. Ammonification
• Conversion of organic nitrogen to ammonia and
  ammonium ions
• 5. Denitrification
• Conversion of nitrate to nitrogen gas

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Nitrogen Cycle
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Atmospheric nitrogen (N2)
1
Nitrogen fixation from human activity
Biological nitrogen fixation (nitrogen-fixing
bacteria in root nodules and soil)
5
Denitrification (denitrifying bacteria)
4
Decomposition (ammonification by ammonifying
bacteria)
Plant and animal proteins
Internal cycling (nitrification,
assimilation, ammonification on land)
Assimilation (nitrates, ammonia, or ammonium
absorbed by roots and used to make organic
compounds)
Ammonia (NH3) and ammonium (NH4)
3
2
Nitrification (Nitrifying bacteria)
Nitrate (NO3-)
Fig. 26-19, p. 532
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Nitrogen Fixation
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Nodules
(a) Root nodules of a garden pea (Pisum sativum),
which is a legume. Rhizobium bacteria live in
these nodules and fix nitrogen, some of which is
used by the host plant.
Fig. 26-20a, p. 533
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Heterocysts
(b) Many cyanobacteria fix nitrogen. Shown is
Anabaena, a cyanobacterium with specialized cells
called heterocysts where nitrogen fixation occurs.
Fig. 26-20b, p. 533
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The Hydrologic Cycle

• Exchange of water between land, ocean,
  atmosphere, and organisms
• Water enters atmosphere by evaporation and
  transpiration
• Leaves atmosphere as precipitation
• On land, water filters through the ground or runs
  off to lakes, rivers, and ocean

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Hydrologic Cycle
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Movement of moist air
Condensation (cloud formation)
Atmosphere
1
Precipitation to ocean
1
Precipitation on land
2
Evaporation from ocean
2
3
Evaporation from soil, streams, rivers, and lakes
Transpiration from vegetation
4
Runoff to ocean
Percolation through soil and porous rock
5
Ocean
Groundwater
Fig. 26-21, p. 534
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LEARNING OBJECTIVE 10

• Distinguish between bottom-up and top-down
  processes

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Bottom-Up Processes

• Availability of resources such as minerals
  controls the number of producers (lowest trophic
  level), which in turn controls the number of
  herbivores, which in turn controls the number of
  carnivores

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Top-Down Processes

• Regulate ecosystems from the highest trophic
  level (consumers eating producers)
• An increase in number of top predators cascades
  down the food web through herbivores and
  producers

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Bottom-Up and Top-Down Processes
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Carnivores
Carnivores
Herbivores
Herbivores
Producers
Producers
Nutrients
Nutrients
(a) Bottom-up processes
(b) Top-down processes
Fig. 26-22, p. 535
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Animation Exponential Growth
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Animation Carbon Cycle
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Animation Hydrologic Cycle
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