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Ecosystems
Chapter 26
LEARNING OBJECTIVE 1
•
Define ecology
•
Distinguish among population,
community, ecosystem, and biosphere
KEY TERMS
•
ECOLOGY
•
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Discipline of biology that studies interrelations
between living things and their environments
Ecologists study populations, communities,
ecosystems, and the biosphere
KEY TERMS
•
POPULATION
•
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A group of organisms of the same species
that live in a defined geographic area at the
same time
COMMUNITY
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An association of populations of different
species living in a defined habitat with some
degree of interdependence
Community: A Nurse Log
KEY TERMS
•
ECOSYSTEM
•
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Interacting system that encompasses a
community and its nonliving, physical
environment
BIOSPHERE
•
All of Earth’s living organisms, collectively
LEARNING OBJECTIVE 2
•
Explain the difference between Jshaped and S-shaped population
growth curves
Dispersion in Populations
(a) Random
dispersion
(b) Clumped
dispersion
(c) Uniform
dispersion
Fig. 26-2, p. 517
Intrinsic Rate of Increase
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The maximum rate at which a population
could increase in number under ideal
conditions
Exponential Population Growth
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J-shaped curve
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An accelerated pattern of growth exhibited
by certain populations for a limited period
Exponential Population Growth
Logistic Population Growth
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S-shaped curve
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After accelerated growth, growth rate
decreases
•
Natural populations seldom follow the
logistic growth curve closely
Logistic Population Growth and
Carrying Capacity
LEARNING OBJECTIVE 3
•
Summarize the three main types of
survivorship curves
Survivorship
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The probability that a given individual in a
population will survive to a particular age
3 General Survivorship Curves
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Type I survivorship
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Type II survivorship
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Mortality greatest in old age
Mortality spread evenly across all age groups
Type III survivorship
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Mortality greatest among the young
Survivorship Curves
Experiment: Drummond Phlox
Metapopulation
LEARNING OBJECTIVE 4
•
Characterize producers, consumers,
and decomposers
KEY TERMS
•
PRODUCER
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An organism that synthesizes organic
compounds from simple inorganic raw
materials
KEY TERMS
•
CONSUMER
•
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An organism that cannot synthesize its own
food from inorganic raw materials
Must obtain energy and body-building
materials from other organisms
KEY TERMS
•
DECOMPOSER
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A microorganism that breaks down dead
organic material and uses the decomposition
products as a source of energy
LEARNING OBJECTIVE 5
•
Describe what is meant by an
organism’s ecological niche
KEY TERMS
•
ECOLOGICAL NICHE
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The totality of an organism’s adaptations, its
use of resources, its interactions with other
organisms, and the lifestyle to which it is fitted
in its community
LEARNING OBJECTIVE 6
•
Define competition, predation, and
symbiosis
•
Distinguish among mutualism,
commensalism, and parasitism
KEY TERMS
•
COMPETITION
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Interaction among two or more individuals that
attempt to use the same essential resource,
such as food, water, sunlight, or living space
KEY TERMS
•
PREDATION
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A relationship in which one organism (the
predator) kills and devours another organism
(the prey)
KEY TERMS
•
SYMBIOSIS
•
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An intimate relationship between two or more
organisms of different species
Symbiosis includes mutualism,
commensalism, and parasitism
Symbiosis
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Mutualism
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Commensalism
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Both partners benefit
One organism benefits
Other is unaffected
Parasitism
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One organism (the parasite) benefits
Other (the host) is harmed
Plant Defense Against Herbivores
Mutualism
Commensalism
LEARNING OBJECTIVE 7
•
Define ecological succession
•
Distinguish between primary
succession and secondary succession
KEY TERMS
•
ECOLOGICAL SUCCESSION
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Sequence of changes in the species
composition of a community over time
Succession
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Primary succession begins in an area
not previously inhabited
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Example: bare rock
Secondary succession begins in an area
where there was a preexisting community
and a well-formed soil
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Example: abandoned farmland
Primary Succession
Lichens
Exposed
and mosses
rocks
Ferns, grasses,
and herbs
Low shrubs
Jack pine,
black spruce,
and aspen
Balsam fir,
paper birch, and
white spruce
forest
community
Fig. 26-12, p. 526
Secondary Succession
LEARNING OBJECTIVE 8
•
Summarize the concept of energy flow
through a food web
KEY TERMS
•
TROPHIC LEVEL
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Each sequential step in a food chain or food
web, from producer to primary, secondary, or
tertiary consumers
Energy Flow
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Energy flows through an ecosystem in one
direction, from sun to producer to
consumer to decomposer
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Energy used for metabolic purposes at a
given trophic level is unavailable to the
next trophic level
Solar Energy
30% reflected back
into space
immediately
Less than one-billionth of the
sun’s total energy
reaches Earth’s outer
atmosphere.
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
Trophic Levels
Energy
from
sun
First
Second
Third
Fourth
tropic level trophic level: trophic level: trophic level: Decomposers
producers:
primary
secondary
tertiary
(saprotrophs)
consumers consumers consumers
Heat
Heat
Heat
Heat
Heat
Fig. 26-15, p. 529
Energy
from
sun
First
Second
Third
Fourth
tropic level trophic level: trophic level: trophic level: Decomposers
producers:
primary
secondary
tertiary
(saprotrophs)
consumers consumers consumers
Heat
Heat
Heat
Heat
Heat
Stepped Art
Fig. 26-15, p. 529
A Food Web
Energy Pyramid
Decomposers
(5060)
Tertiary consumers (21)
Secondary consumers (383)
Primary consumers (3368)
Producers
(20,810)
Fig. 26-17, p. 531
LEARNING OBJECTIVE 9
•
Describe the main steps in the carbon,
nitrogen, and hydrologic cycles
KEY TERMS
•
BIOGEOCHEMICAL CYCLE
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Process by which matter cycles from the living
world to the nonliving, physical environment
and back again
The Carbon Cycle
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Carbon dioxide gas (CO2) enters plants,
algae, and cyanobacteria
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Which incorporate it into organic molecules
through photosynthesis
Cellular respiration, combustion, erosion of
limestone return CO2 to water and atmosphere
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Making it available to producers again
Carbon Cycle
Air (CO2)
2
Soil
2
2
Animal and
microorganism Decomposition
plant respiration
respiration
1
Photosynthesis
by land plants
5
Combustion
(human and natural)
Marine
plankton
remains
Soil
Partly
decomposed
plant remains
3
Coal
4
Natural gas
6
Dissolved
Erosion of CO2 in water
limestone to
Shells of
marine
form dissolved
organisms:
Coal
CO2
burial
and compaction
7 to form rock
(limestone)
Oil
Fig. 26-18, p. 531
The Nitrogen Cycle
1. Nitrogen fixation
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Conversion of nitrogen gas to ammonia
2. Nitrification
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Conversion of ammonia or ammonium to nitrate
3. Assimilation
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Conversion of nitrates, ammonia, or ammonium
to proteins, chlorophyll, and other nitrogencontaining compounds by plants
The Nitrogen Cycle
4. Ammonification
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Conversion of organic nitrogen to ammonia
and ammonium ions
5. Denitrification
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Conversion of nitrate to nitrogen gas
Nitrogen Cycle
Atmospheric
nitrogen (N2)
1
Biological nitrogen fixation Nitrogen fixation
(nitrogen-fixing bacteria from human activity
in root nodules and soil)
5
Denitrification
(denitrifying bacteria)
4
Decomposition
(ammonification by
ammonifying bacteria)
Plant and animal proteins
Internal cycling
(nitrification, assimilation,
Assimilation
(nitrates, ammonia, or
ammonification on land)
ammonium absorbed by roots and
used to make organic compounds)
Ammonia (NH3)
and ammonium (NH4+)
2
Nitrification
(Nitrifying bacteria)
3
Nitrate (NO3−)
Fig. 26-19, p. 532
Nitrogen Fixation
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
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
The Hydrologic Cycle
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Exchange of water between land, ocean,
atmosphere, and organisms
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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
Hydrologic Cycle
Movement of
moist air
Condensation
Atmosphere
(cloud formation)
1
Precipitation
to ocean
1
Precipitation
on land
2
Evaporation
from ocean
2
Evaporation from soil,
streams, rivers, and lakes
3
Transpiration
from vegetation 4
Runoff
to ocean
5 Percolation
through soil
and porous rock
Ocean
Groundwater
Fig. 26-21, p. 534
LEARNING OBJECTIVE 10
•
Distinguish between bottom-up and
top-down processes
Bottom-Up Processes
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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
Top-Down Processes
•
Regulate ecosystems from the highest
trophic level (consumers eating producers)
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An increase in number of top predators
cascades down the food web through
herbivores and producers
Bottom-Up and Top-Down Processes
Carnivores
Carnivores
Herbivores
Herbivores
Producers
Producers
Nutrients
Nutrients
(a) Bottom-up processes
(b) Top-down processes
Fig. 26-22, p. 535
Animation: Exponential Growth
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Animation: Carbon Cycle
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Animation: Hydrologic Cycle
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