Download Ecosystems and Environment

Hewitt/Lyons/Suchocki/Yeh
Conceptual Integrated
Science
Chapter 21
ECOSYSTEMS AND
ENVIRONMENT
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This lecture will help you
understand:
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Organisms and Their Environment
Species Interactions
Science and Society: Species Interactions
Science and Society: Invasive Species
Energy Flow in Ecosystems
Integrated Science: Materials Cycling
Kinds of Ecosystems
Change in an Ecosystem
Population Studies
Human Population Growth
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Organisms and Their Environment
Ecology is the study of how organisms
interact with their environments.
The environment includes abiotic
(nonliving) and biotic (living) components.
We study ecology at many levels, including
the individual, population, community, and
ecosystem.
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Organisms and Their Environment
CHECK YOUR NEIGHBOR
Prairie dogs living in Nebraska represent:
A. A species
B. A population
C. A community
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Organisms and Their Environment
CHECK YOUR ANSWER
Prairie dogs living in Nebraska represent:
A. A species
B. A population
C. A community
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Species Interactions
Food chains and food webs describe which
species eat which other species. These feeding
levels—called trophic levels—include
producers and consumers.
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Species Interactions
Other types of species interactions include:
• Competition—species compete when their
niches overlap.
• Symbiosis—species may live in close
association with one another. A symbiotic
relationship may involve parasitism,
commensalism, or mutualism.
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Science and Society: Species
Interactions
Studies show that diverse communities are
more stable and more productive.
• More species means greater redundancy
in a community.
• Diverse communities might be more
productive because different species use
resources in different ways.
• It is harder for new species to successfully
invade a diverse habitat.
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Science and Society: Invasive
Species
Invasive species are species that are introduced from
their native habitat into a new habitat and that proceed to
thrive there. This results in harm to native species.
Invasive species:
• Usually are unintentionally introduced (at least these
days)
• May out-compete or devour native species
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Energy Flow in Ecosystems
All organisms need energy in order to grow, reproduce, and perform the
activities necessary for survival.
The amount of organic matter in an ecosystem is its biomass.
The rate at which an ecosystem’s producers build biomass is the
ecosystem’s primary productivity.
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Energy Flow in Ecosystems
On average, only about 10 percent of the energy at one
trophic level becomes available to the next level. The
other 90 percent is:
• Uneaten organisms
• Heat lost to the environment
• Feces
• Maintenance
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Integrated Science: Energy Leaks
Where Trophic Levels Meet
• Moving energy from one trophic level to another involves
a long series of chemical reactions.
• Because every chemical reaction involves some energy
loss to the environment, we see why so much energy
leaks from one trophic level to the next.
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Kinds of Ecosystems
There are terrestrial and aquatic ecosystems.
Terrestrial ecosystems are called biomes.
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Kinds of Ecosystems
There are eight biomes on Earth:
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Tropical forests
Temperate forests
Coniferous forests
Tundra
Savannas
Temperate grasslands
Chaparral
Deserts
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Kinds of Ecosystems
CHECK YOUR NEIGHBOR
True or false? Deserts are not always
located in a band around 30 degrees north
latitude and 30 degrees south latitude.
Explain your answer to your neighbor.
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Kinds of Ecosystems
CHECK YOUR ANSWER
True. Deserts are defined by the low level of
precipitation they receive. Some deserts,
including the continent of Antarctica, are
located far from the equator. Like all
deserts, Antarctica receives very little
precipitation. When it falls, it is in the form
of snow.
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Kinds of Ecosystems
Aquatic ecosystems include freshwater and
saltwater environments as well as
estuaries where freshwater and saltwater
meet.
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Kinds of Ecosystems
All lakes and ponds can be divided into three zones:
• The littoral zone—close to the water surface and to shore, relatively
warm because of its exposure to sunlight.
• The limnetic zone—close to the water surface but far from shore,
occupied largely by plankton, organisms that float in the water rather
than swim actively.
• The profundal zone—deep water habitats in ponds and lakes. Most
organisms in the profundal zone consume organic debris that drifts
down from above.
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Kinds of Ecosystems
Species that live in the flowing waters of
rivers and streams usually have
adaptations that allow them to keep from
being washed away: hooks, suckers,
strong swimming ability.
Algae often occupy the base of the food
chain in river and stream habitats.
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Kinds of Ecosystems
Estuaries are habitats where freshwater rivers join
oceans.
Estuarine plants, such as certain seaweeds, marsh
grasses, and mangroves, have adaptations that
allow them to deal with changing salinity
conditions.
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Kinds of Ecosystems
Ocean habitats are divided by either the depth in the water column or
proximity to shore.
Many species are found in the pelagic zone—either in the photic zone
close to the water surface or the deeper aphotic zone, which
receives little sunlight and is much more limited in food availability
and biodiversity.
The vast majority of marine species are found not in the pelagic zone
but in the benthic zone on the ocean bottom.
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Kinds of Ecosystems
The intertidal zone: closest to shore, periodically
underwater and exposed to air as the tide
moves in and out. Many species, including
certain barnacles, sea anemones, starfish, and
other species, are specialized for life in the
intertidal zone.
The neritic zone: underwater marine habitats near
the coasts, such as coral reefs. The neritic zone
contains high levels of nutrients that have
washed into the water from land.
Farther out is the deeper oceanic zone.
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Integrated Science: Materials
Cycling
Many substances on Earth travel through a
continuous cycle from living organisms to
the abiotic environment and back—these
are biogeochemical cycles.
Three of these cycles involve water, carbon,
and nitrogen.
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Integrated Science: Materials
Cycling
The water cycle:
• Water evaporates from the
oceans into the atmosphere.
• Water is moved around the
atmosphere by winds.
• Water precipitates as rain or
snow over ocean or land.
• Water moves into the biotic
world when it is absorbed or
swallowed by organisms. Some
of this water then passes up the
food chain. The rest is returned
to the abiotic environment in a
variety of ways, including
through animal respiration,
perspiration, excretion, and
elimination, and evaporation
from plant tissue.
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Integrated Science: Materials
Cycling
The carbon cycle:
• Most of the inorganic carbon on
earth exists as carbon dioxide and is
found either in the atmosphere or
dissolved in ocean waters.
• Plants and other producers convert
carbon dioxide to glucose during
photosynthesis.
• Carbon is returned to the
environment by living organisms as
carbon dioxide, a product of cellular
respiration.
• Because atmospheric carbon
dioxide traps heat on the planet, this
has resulted in global warming.
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Integrated Science: Materials
Cycling
The nitrogen cycle:
• Nitrogen is found primarily as
nitrogen gas, the dominant
component of the Earth’s
atmosphere.
• In order for living organisms to
make use of nitrogen, it has to
be converted into usable form.
Living organisms rely on
bacteria to accomplish this
transformation. Nitrogen is
converted to ammonium by
nitrogen-fixing bacteria in soil,
and then to nitrates by
nitrifying bacteria.
• Nitrogen returns to the abiotic
environment when it is
converted back to nitrogen gas
by denitrifying bacteria.
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Change in an Ecosystem
Ecological succession describes how the
species composition of an ecosystem
changes after a disturbance.
Ecological succession is sometimes divided
into two types, primary succession and
secondary succession.
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Change in an Ecosystem
Primary succession: the colonization of bare land devoid of soil; may occur
when new land is formed by volcanic activity or when a glacier’s retreat
reveals bare rock.
Early colonizers of new habitat, known as pioneer species, must survive with
few nutrients and little existing organic matter, cope with direct sunlight, and
survive the variable temperatures that result from lack of cover.
Pioneer species are often succeeded by grasses, shrubs, and finally, trees.
Ecological succession culminates in a climax community.
During the process of succession, the total biomass of the ecosystem typically
increases, as does the number of species.
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Change in an Ecosystem
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Change in an Ecosystem
Secondary succession occurs when a disturbance destroys existing life
in a habitat, but leaves soil intact.
Examples: fires, abandonment of
old farmland
Because soil is already present,
secondary succession
proceeds more quickly
than does primary
succession.
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Change in an Ecosystem
Intermediate disturbance hypothesis—
Regular disturbances, if not too extreme,
actually contribute to biodiversity because
different species make use of different
habitats, and periodic disturbances
guarantee that there will always be habitat
at varying stages of recovery.
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Population Studies
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Population Studies
CHECK YOUR NEIGHBOR
A population is a group of individuals
belonging to a single species that
occupies a certain area.
What are some populations in your area?
Discuss with your neighbor.
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Population Studies
Population size over time depends on four
variables—birth rate, death rate, the rate
of immigration into the population, and the
rate of emigration out of the population.
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Population Studies
Exponential growth occurs when a
population grows at a rate that is
proportional to its size.
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Population Studies
Logistic growth occurs when population
growth slows as it reaches the habitat’s
carrying capacity, the maximum number
of individuals or maximum population
density the habitat can support.
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Population Studies
Organisms have different life history strategies.
r-selected organisms produce a lot of offspring and invest little
in each offspring. For example, they provide little parental
care. Few of the offspring reach adulthood.
K-selected organisms produce a few offspring and provide a
great deal of investment in each. For example, they provide a
lot of parental care. Most of their offspring reach adulthood.
Of course, these are two extremes along a continuum.
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Population Studies
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Human Population Growth
Human population is currently about 6.5 billion.
Although world population continues to grow rapidly, the rate of
growth has slowed, so that growth is no longer exponential.
Scientists now believe that if present trends continue, the global
human population will peak at around 10 billion soon after
2050.
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Human Population Growth
Some human populations have undergone a demographic
transition, a shift from high birth and death rates to low
birth and death rates.
Usually, death rate decreases first, due to medical and
public health advances. Later, birth rate also declines.
During the period between the fall in death rate and the fall
in birth rate, the combination of low death rate and high
birth rate causes the population to grow very rapidly.
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Human Population Growth
A pyramid-shaped age structure diagram, such as that of
Kenya, is a sign of a rapidly growing population. Most of
the population is young and therefore at or approaching
reproductive age.
The United States has an age structure that is much more
even—its population is growing slowly.
In Italy, much of the population is older, and there are
relatively few children. Italy’s population is stable or even
declining.
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Human Population Growth
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Human Population Growth
AIDS has affected world population more than any
other disease since the bubonic plague of the
Middle Ages.
AIDS strikes primarily adults of reproductive age.
Some of the countries struck hardest by AIDS,
including Botswana and South Africa, are
expected to experience population declines as a
result of the disease.
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