Download Ch. 37

The Living World
Fifth Edition
George B. Johnson
Jonathan B. Losos
Chapter 37
Ecosystems
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
37.1 Energy Flows Through
Ecosystems
• Ecology is the study of the interactions of
living organisms with one another and with
their physical environment
 a community is the collection of organisms
that live in a particular place
 the place where a community lives is called
the habitat
 the combination of the community and habitat
is called the ecosystem
37.1 Energy Flows Through
Ecosystems
• The ecosystem is the most complex level
of biological organization
 the biosphere is the sum of all of the
ecosystems on earth
 the earth is a closed system with respect to
chemicals but an open system in terms of
energy
 organisms in ecosystems regulate the capture
and expenditure of energy and the cycling of
chemicals
37.1 Energy Flows Through
Ecosystems
• You can think of the organisms in an
ecosystem as chemical machines fueled
by energy captured in photosynthesis
 producers first capture the energy
• these are the autotrophs, such as plants, algae,
and some bacteria
 consumers are the heterotrophs that obtain
their energy-storing molecules by consuming
plants or other animals
37.1 Energy Flows Through
Ecosystems
• Ecologists assign every organism in an
ecosystem to a trophic level
 a trophic level is a feeding level composed of those
organisms whose source of energy is the same
number of consumption “steps” away from the sun
 food energy passes through an ecosystem from one
trophic level to another
• when the path is a simple linear progression, it is called a
food chain
• the chain ends with decomposers that break down dead
organisms
Figure 37.1 Trophic levels within an
ecosystem
37.1 Energy Flows Through
Ecosystems
• In most ecosystems, the path of energy is
not linear because individuals often feed at
several trophic levels
 a food web describes this more complex path
of energy flow
37.2 A food web
37.1 Energy Flows Through
Ecosystems
• Producers
 the lowest trophic level of any ecosystem
 green plants occupy this role in most terrestial
ecosystems while algae do this in most aquatic
systems
• Herbivores
 occupy the second trophic level and eat producers
 they are the primary consumers
37.1 Energy Flows Through
Ecosystems
• Carnivores
 occupy the third trophic level and eat producers are secondary
consumers
 some carnivores also eat plants, and are called omnivores
• Detrivores are special consumers that eat dead
organisms
 also known as scavengers
• Decomposers are organism that break down organic
substances, making them available to other organisms
 bacteria and fungi are the principal decomposers in land
ecosystems
Figure 37.3 Members of the food
chain
37.1 Energy Flows Through
Ecosystems
• Primary productivity is the total amount of light energy
converted by producers into organic compounds in a
given area per unit of time
• Net primary productivity is the total amount of energy
fixed by photosynthesis per unit time minus that
expended by photosynthetic organisms to fuel metabolic
activities
• Biomass is the total weight of all ecosystem organisms
and increases as a result of the ecosystems net primary
productivity
37.1 Energy Flows Through
Ecosystems
• Much of the energy
captured by the plant
is lost as energy
passes through the
ecosystem
• 80% to 95% of the
energy available at
one trophic level is
not transferred to the
next
Figure 37.4 How heterotrophs
use food energy
37.1 Energy Flows Through
Ecosystems
• Food chains usually consist of only three
or four steps
 so much energy is lost at each step that very
little energy remains in the system after it has
been incorporated into the bodies of
organisms at four successive trophic levels
Figure 37.5 Energy loss in an
ecosystem
37.2 Ecological Pyramids
• There are generally far more individuals at the
lower trophic levels than at the higher levels
 plants fix about 1% of the sun’s energy into their
green parts
 consumers process into their own bodies only about
10% of the energy available in the organisms on
which they feed
• Similarly, the biomass of primary producers is
greater than that of higher trophic levels
Figure 37.6 (a,b) Ecological
pyramids
37.2 Ecological Pyramids
• Some aquatic ecosystems have inverted
pyramids because the turnover of
phytoplankton producers being consumed
by zooplankton is very high
 the phytoplankton can never build a large
biomass; also they still produce the largest
amount of energy
Figure 37.6 (c,d) Ecological
pyramids
37.2 Ecological Pyramids
• The loss of energy that occurs at each
trophic level places a limit on many toplevel carnivores a community can support
 top-level predators tend to be relatively large
animals
 because only 1/1000th of the original energy
captured by photosynthesis is available to a
tertiary consumer
• so top-level predators have no predators that
subsist exclusively on them
37.3 The Water Cycle
• Unlike energy, the physical components of
ecosystems are passed around and
reused within ecosystems
 this is termed cycling by ecologists
 the paths of water, carbon, and soil nutrients
as they pass from the enviromnent to living
organisms and back form closed
biogeochemical cycles
37.3 The Water Cycle
• Of all the nonliving components of an
ecosystem, water has the greatest influence on
the living portion
 water cycles within an ecosystem in two ways
• environmental water cycle
– water vapor in the atmosphere condenses and falls to earth as
precipitation
– it reenters the atmosphere by evaporation from lakes, rivers,
and oceans
• organismic water cycle
– surface water does not return to the atmosphere but is instead
uptaked by plant roots
– after passing through the plant, it evaporates from a plant leaf
via transpiration
Figure 37.7 The water cycle
37.3 The Water Cycle
• Deforestation breaks the water cycle
 in especially dense forest ecosystems, such
as tropical rain forests, 90% of the moisture in
the atmosphere is taken up by plants and
returned by transpiration
 the vegetation is actually the primary source
of local rainfall
 when forests are cut down the moisture is not
returned to the atmosphere
Figure 37.8 Burning or clear-cutting
forests breaks the water cycle
37.3 The Water Cycle
• In the US more than 96% of the freshwater
is in the form of groundwater
 groundwater occurs in permeable, saturated,
underground layers of rock, sand, and gravel
called aquifers
 the increasing chemical pollution and use of
groundwater is becoming a very serious
problem
37.4 The Carbon Cycle
• The earth’s atmosphere contains plentiful
carbon, present as CO2
 the carbon cycles between the atmosphere
and living organisms
• plants trap the carbon in organic molecules by
photosynthesis
• the carbon is returned to the atmosphere by
respiration, combustion, and erosion
– some carbon is locked up for a long time as fossils
– the burning of fossil fuels leads to some of this carbon
being released back to the atmosphere
Figure 37.9 The carbon cycle
37.5 Soil Nutrients and Other
Chemical Cycles
• Organisms contain a lot of nitrogen (a
principal component of protein) and so
does the atmosphere
 most living organisms cannot use the main
form of nitrogen in the atmosphere, N2 gas
• the two nitrogen atoms of N2 are bound by a triple
bond that is hard to break
• some bacteria can break this bond, and add the N
to H atoms, forming ammonium (NH4+)
– this process is called nitrogen fixation
37.5 Soil Nutrients and Other
Chemical Cycles
• Nitrogen fixation can only take place in the
absence of oxygen
 nitrogen-fixing bacteria are found in cysts that
admit no oxygen or within airtight nodules of
certain plants, such as beans
 the availability of fixed nitrogen in fields is
very limited
• farmers supplement their fields through adding
fertilizers
37.5 Soil Nutrients and Other
Chemical Cycles
• Phosphorous is another soil nutrient that is important to
organisms because it is a key part of both ATP and DNA
 phosphorous does not form a gas and is not available in the
atmosphere
 most of the phosphorous in ecosystems is taken up by
organisms
 the phosphorous level of freshwater lake ecosystems is usually
very low, which limits the growth of photosynthetic algae
• If P-containing fertilizers or detergents pollute a lake, rapid
uncontrolled blooms of algae result in a process called
eutrophication
• the excess algae soon die and then bacteria decomposing the algae
use up the lake’s dissolved O2, killing other organisms
Figure 37.11 The phosphorus cycle
37.6 The Sun and Atmospheric
Circulation
• The earth’s annual orbit around the sun
and its daily rotation on its own axis are
important in determining the world climate
 the tropics are warmer than the temperate
regions because the sun’s rays arrive almost
perpendicular at regions near the equator
 because of the annual cycle and the
inclination of the earth’s axis, all parts away
from the equator experience a progression of
seasons
Figure 37.12 Latitude affects
climate
In this view of the earth, the Southern Hemisphere is tilted more towards the
sun and is experiencing summer.
37.6 The Sun and Atmospheric
Circulation
• The major atmospheric circulation patterns
result from the interactions between six
large air masses
 these air masses affect climate because the
rising and falling of an air mass influence its
temperature, which, in turn, influences its
moisture-holding capacity
Figure 37.13 Air rises at the
equator and then falls
37.7 Latitude and Elevation
• Temperature varies with elevation, with
higher elevations becoming progressively
cooler
 at any given latitude, air temperature falls
about 6C for every 1,000-meter increase in
elevation
Figure 37.14 How elevation affects
ecosystems
37.7 Latitude and Elevation
• When a moving body of air ecounters a
mountain, it is forced upward, and as it is
cooled at higher elevation, produces rain
on the windward side of a mountain
 as the air passes the peak and descends on
the far side of the mountains, its moistureholding capacity increases
 the air dries the surrounding landscape, often
producing a desert
• this effect is often called a rain shadow
Figure 37.15 The rain shadow
effect
37.8 Patterns of Circulation in the
Ocean
• Patterns of oceanic circulation are
determined by the patterns of atmospheric
circulation
 oceanic circulation is dominated by the
movement of surface water in huge spiral
patterns called gyres
• for example, the Gulf stream
 gyres move clockwise in the Northern
Hemisphere and counterclockwise in the
Southern Hemisphere
Figure 37.16 Oceanic circulation
37.8 Patterns of Circulation in the
Ocean
• El Niño
 occurs every two to seven years and is a warming of
Pacific waters caused by a shift in winds that normally
carry warm water from east to west
 the resulting warming will cause an increase in winter
storms to the CA coast and a wetter and colder winter
in the FL and Gulf coast areas
• La Niña
 is the opposite of El Niño and is a period of unusually
cold temperature in the eastern Pacific
Figure 37.17 An El Niño winter
37.9 Ocean Ecosystems
• The oceans have an average depth of
more than 3 km and they are, for the most
part, cold and dark
 photosynthetic organisms are confined to the
upper few hundred meters because light does
not penetrate any deeper
 almost all organisms that live below this level
feed on organic debris from above
37.9 Ocean Ecosystems
• There are three main types of ocean ecosystems
 shallow water
• the small area of water that occurs mostly along the shoreline and
contains the most species
• part of this area consists of the intertidal zone, which is periodically
exposed to air
• partly enclosed bodies of water, such as river mouths and coastal
bays, have intermediate salinities and are called estuaries
 open-sea surface
• contains a lot of phytoplankton that drift with the current and perform
40% of all the photosynthesis that takes place on earth
 deep-sea water
• Very few organisms live below 300 meters and are often bizarre
Figure 37.18 Ocean ecosystems
37.9 Ocean Ecosystems
• In the deep-sea ecosystem
 many inhabitants are bioluminescent for the
purpose of communication or predation
 many are specialized to a local area (i.e.,
endemic)
 while some utilize energy falling to the ocean
floor as debris from above, some deep-sea
inhabitants are autotrophic
• they derive energy from hydrothermal vent
systems
Figure 37.20 Deep-sea waters
37.10 Freshwater Ecosystems
• Freshwater ecosystems include lakes,
ponds, rivers, and wetlands
 they are limited in area
 all freshwater habitats are strongly connected
to land habitats with wetlands (i.e., marshes
and swamps) constituting intermediate
habitats
 a large amount of organic and inorganic
material continually enters bodies of
freshwater from nearby land communities
Figure 37.21 A nutrient-rich stream
37.10 Freshwater Ecosystems
• Ponds and lakes have
three zones in which
organisms live
• Littoral (shallow “edge”)
• Limnetic (open-water
surface)
• Profundal (deep-water)
• no light penetrates here
Figure 37.23 The three zones in
ponds and lakes
37.10 Freshwater ecosystems
• In temperate regions, large lakes undergo
thermal stratification, a process in which water
at 4C sinks below water that is either cooler or
warmer
 this is because 4C is when water is most dense
 overturns, when the deeper waters of the lake come
to the surface as the denser surface waters sink,
occur in the spring and fall
• this brings up fresh supplies of nutrients to the surface waters
Figure 37.24 Spring and fall overturns
in freshwater ponds and lakes
37.10 Freshwater Ecosystems
• The thermocline in a lake is where the cooler and
warmer layers meet and is an abrupt temperature
change
• Lakes can be divided into two categories, based on their
production of organic materials
 eutrophic lakes have an abundant supply of minerals and
organic matter
• they have little oxygen at deep depths but are reinfused at overturns
 oligotrophic lakes have little scarce minerals and organic
matter
• because they are deeper, they always have deep waters rich in
oxygen
37.11 Land Ecosystems
• A biome is a terrestrial ecosystem
 each biome is characterized by a particular climate
and a defined group of organisms
 the biomes differ remarkably from each other but
show many consistencies within
• a particuar biome often looks similar, with many of the same
creatures living there, wherever it occurs on the earth
 there are seven major and seven minor biomes
distributed throughout the earth
• biomes that normally occur at high latitudes also follow an
altitudinal gradient along mountains
Figure 37.25 Distribution of the
earth’s biomes
37.11 Land Ecosystems
• Tropical rain forests
are the richest
ecosystems on earth
• Communities in these
forests are very
diverse in that each
type of organism is
represented by a few
individuals
Figure 37.26 Tropical rain
forest
37.11 Land Ecosystems
• Savannas are
grasslands that have
widely spaced trees
and seasonal rainfall
• This biome is a
transition between
tropical rain forest
and desert
Figure 37.27 Savanna.
37.11 Land Ecosystems
• Deserts are dry
places with sparse
vegetation
• Plants and animals
may restrict their
activity to favorable
times of the year,
when water is present
Figure 37.28 Desert
37.11 Land Ecosystems
• Grasslands (also
called prairies) grow
in temperate areas
• Most of the original
grasslands have been
converted to use by
agriculture
Figure 37.29 Temperate grassland.
37.11 Land Ecosystems
• Deciduous forests
are forests of trees
that drop their leaves
in the winter
Figure 37.30 Temperate deciduous
forest.
37.11 Land Ecosystems
• The taiga is a great
ring of coniferous
trees that extends
across vast areas of
North America and
Asia
• Most of the trees
occur in dense stands
of one or two species
Figure 37.31 Taiga.
37.11 Land Ecosystems
• Tundra is open, often
boggy, grassland that
occurs in the far north
beyond the taiga
• Permafrost, or
permanent ice,
usually exists within
1 meter of the surface
Figure 37.32 Tundra
37.11 Land Ecosystems
• Chapparal consists
of evergreen, often
spiny shrubs and low
trees
• These communities
occur a dry summer
climate, also known
as Mediterranean
Figure 37.33 Chaparral
37.11 Land Ecosystems
• Polar ice caps lie
over the Arctic Ocean
in the north and the
Antarctica in the
south
• This region receives
almost no
precipitation and
freshwater is scarce
Figure 37.34 Polar ice
37.11 Land Ecosystems
• Tropical upland forests
occur at slightly higher
altitudes than rainforest
or where local climates
are drier
• Rainfall is seasonal
 monsoon season brings
rainfall from the oceans
into the interior
Figure 37.35 Tropical monsoon
forest
37.11 Land Ecosystems
• Semidesert areas occur
in regions with less rain
than monsoon forests but
more rain than savannas
• Vegetation is dominated
by bushes and trees with
thorns and this biome is
also known as
thornwood forest
• The biome is found on
the edges of desert
biomes
Figure 37.36 Semidesert
37.11 Land Ecosystems
• There are three additional minor biomes
 mountain (alpine) zone
• similar to tundra but at high altitude
 temperate evergreen forest
• occurs in regions where winters are cold and there
is a strong, seasonal dry period
 warm, moist evergreen forest
• occur in regions where winters are mild and
moisture is plentiful
Inquiry & Analysis
• How does the loss of
nitrogen from the
ecosystem in the cut
forest compare with
nitrogen loss from the
uncut forest?
Graph of The Hubbard Brook
Deforestation Experiment