Po l2e ch41 lecture the distribution of earths ecological systems edited sphs

The Distribution of Earth’s
Ecological Systems
41

Chapter 41 The Distribution of Earth’s Ecological Systems
Key Concepts
41.1 Ecological Systems Vary over Space and Time
41.2 Solar Energy Input and Topography Shape
Earth’s Physical Environments
41.3 Biomes: Biogeography Reflects Physical
Geography
41.4 Biogeography Also Reflects Geological History
41.5 Human Activities Affect Ecological Systems on a
Global Scale

Chapter 41 Opening Question
Can basic ecological principles suggest why
removing cattle has not restored grasses
to the Borderlands?

Concept 41.1 Ecological Systems Vary over Space and Time
Physical geography—study of the spatial
distribution of Earth’s climates and surface
features
Biogeography—study of the spatial distributions
of species
The explorer/scientists in the 18th
and 19th
centuries began to realize that the distributions of
species and environments are linked.

Abiotic components (abiotic factors) of the
environment are nonliving.
Biotic components (biotic factors)—living
organisms
An ecological system—one or more
organisms plus the external environment with
which they exchange energy and materials.

Ecology is the scientific study of the interactions
between organisms and the environment
These interactions determine both the distribution of
organisms and their abundance
“Ecology” was coined by Ernst Haeckel in 1866; he
helped establish it as a formal science.
He also emphasized ecology’s relevance to Darwin’s
theory of evolution by natural selection.
Who coined the the term “ecology?”

A system is defined by the interacting parts it
contains.
Ecological systems can include any part of the
biological hierarchy from the individual to the
biosphere.
Each level brings in new interacting parts at
progressively larger spatial scales.
Ecologists use observations and experiments to test
explanations for the distribution and abundance of
species

At the smallest scale is the individual organism and its
immediate environment.
Individuals remove materials and energy from the
environment, convert them into forms that can be
used by other organisms, and, by their presence and
activities, modify the environment.
The environment of any organism includes abiotic
(nonliving) components, and biotic (living)
components, and all the organisms living in the
environment (biota).

Organismal ecology studies how an individual
organism's structure, physiology, and (for
animals) behavior meet the challenges posed by
the environment
(a) Organismal ecology. How do humpback whales select their
calving areas?

Population—group of individuals of the same
species that live, interact, and reproduce in a
particular geographic area
Community—assemblage of interacting
populations of different species in one area
Landscapes include multiple communities.
Biosphere—all the organisms and
environments of the planet
Which level of organization must include members from
only a single species?

Population ecology concentrates mainly on
factors that affect how many individuals of a
particular species live in an area

Community ecology deals with the whole array of
interacting species in a community

Ecologists replace the term “ecological system” with ecosystem
when they are explicitly including the abiotic components of the
environment;
And in particular when considering communities and their
environmental context.
An ecosystem is all of the organisms in a community plus the
abiotic factors.
Ecosystems are transformers of energy and processors of matter.
• Capture energy
• Transfer energy
• Cycle nutrients

Ecosystem ecology emphasizes energy flow and
chemical cycling among the various biotic and
abiotic components

Landscape ecology deals with arrays of
ecosystems and how they are arranged in a
geographic region
(e) Landscape ecology. To what extent do the trees lining the drainage
channels in this landscape serve as corridors of dispersal for forest
animals?

Most ecologists follow the precautionary principle
regarding environmental issues
The precautionary principle basically states that
humans need to be concerned with how their actions
affect the environment.

Generally, large ecological systems tend to be
more complex because they have more
interacting parts, and larger spatial scale.
But small systems can also be complex:
• The human gut is densely populated with
hundreds of microbial species. These cells
far outnumber the trillion or so human cells
in the body.

Example:
The mammalian gut environment provides stable
conditions and ample nutrients.
Gut microbes metabolize foods, including some the
host cannot digest, and excrete waste products that
provide nutrition to the host or to other microbes.
Microbial species interact with one another and with
host cells by forming biofilms that coat the gut lining.

Biotic and abiotic components of ecosystems are
distributed unevenly in space, and ecosystems can
change over time.
The human gut illustrates this variation—each person
has a unique gut community.
But patterns do exist: gut communities of genetically
related people are more similar that those of
unrelated people.

Gut communities in lean people
and obese people vary in the
ratio of two bacterial phyla.
When obese people lose weight,
their gut community becomes
more similar to that of a lean
person.
Bacteria in the phylum Firmicutes
are good at breaking down
indigestible polysaccharides and
extracting more energy from
food than Bacteroidetes.

Figure 41.1 Genetics and Diet Affect the Composition of the Gut Microbial Community

Experiment:
In experiments with mice, it has been shown
that the gut community contributes to obesity,
along with diet and genetic factors.

Figure 41.2 The Microbial Communities of Genetically Obese Mice Contribute to Their
Obesity (Part 1)

Obesity (Part 2)

Obesity (Part 3)

Concept 41.2 Solar Energy Input and Topography Shape
Earth’s environments vary greatly from place to
place and also through time.
On long time scales, the coming and going of
oceans, ice ages, and other geologic events
shape environments.
On short time scales, physical conditions depend
largely on solar energy input, which drives the
circulation of the atmosphere and the oceans.

Weather is the state of atmospheric conditions
in a particular place at a particular time.
Climate is the average conditions and patterns
of variation over longer periods.
Climate is what you expect; weather is what you
get.
Adaptations to climate prepare organisms for
expected weather patterns.
The long-term average atmospheric conditions of a
region are referred to as its _______________.

Earth receives uneven inputs of solar radiation due
to its spherical shape and the tilt of its axis as it
orbits the sun.
• It is colder at the poles because there is less
solar input: the sun’s rays are spread over a
larger area and pass through more atmosphere.
• High latitudes experience more seasonality—
greater fluctuation over the course of a year.

Figure 41.3 Solar Energy Input Varies with Latitude

Figure 41.4 The Tilt of Earth’s Axis of Rotation Causes the Seasons
When do the Northern and Southern Hemispheres receive the
same amount of sunlight?

Solar energy inputs are always greatest in the tropics
and decrease poleward.
This latitudinal gradient drives global circulation
patterns in the atmosphere.

Hadley cells:
• The tropical air is warmed, rises, and then
cools adiabatically (an expanding gas cools).
• The rising warm air is replaced by surface air
flowing in from the north and south.
• The cooling air sinks at 30°N and 30°S.
The term “adiabatic” usually refers to what?

Figure 41.5 Tropical Solar Energy Input Sets the Atmosphere in Motion
At which
latitude
would
you most
likely find
deserts?

Hadley cell circulation
produces latitudinal
precipitation patterns:
• Rising warm tropical air
releases lots of moisture
as rainfall. The sinking
air at 30°N and 30°S is
dry—most of the great
deserts are at these
latitudes.

Some of the descending air in the Hadley cells flows
towards the poles, overriding cold, dense polar air
that is flowing equatorward.
The interaction of these warm and cold air masses
generates winter storms that sweep from west to
east through the middle latitudes.
Earth’s rotation adds an east–west component to the
north–south movement of the air masses—the
Coriolis effect.

Figure 41.6 Global Atmospheric Circulation and Prevailing Winds
-In what way would an area at 60 degrees latitude (North or South)
most likely resemble an area near the equator?
-An air mass moving north will be deflected in which direction?
-Winds in the middle (40–60N) latitudes of the Northern Hemisphere
generally come which direction?

These atmospheric circulation patterns affect
climate patterns by transferring heat energy from
the hot tropics to the cold poles.
Without this transfer, the poles would sink toward
absolute zero in winter, and the equator would
reach fantastically high temperatures throughout
the year.

Prevailing surface winds drive the major ocean
surface currents, which carry materials,
organisms, and heat with them.
• Example: In the northern tropics, the trade
winds drag water to the west; when it reaches
a continent, it is deflected northward until the
westerlies drive the water back to the east.
The result is a clockwise gyre.
If the rotational speed of Earth decreased somewhat, the most likely
result would do what to the prevailing winds?

Figure 41.7 Ocean Surface Currents

As they move poleward, tropical surface waters
transfer heat from low to high latitudes, adding
to the heat transfer by atmospheric circulation.
The Gulf Stream and North Atlantic Drift bring
warm water towards northern Europe,
warming the air there. The same latitudes in
Canada are much colder.

Deep ocean currents are driven by water
density differences.
Colder, saltier water is more dense and sinks to
form deep currents.
Deep currents regain the surface in areas of
upwelling, completing a vertical ocean
circulation.

Oceans and large lakes moderate terrestrial climates
because water has a high heat capacity:
• Temperature of water changes slowly as it
exchanges heat with the air.
Water temperatures fluctuate less than land
temperatures, and the air over land close to oceans or
lakes also shows less seasonal and daily temperature
fluctuation.
Because oceans have a (low or high) heat capacity, air over land
that is close to oceans shows (increased or decreased) variability of
temperature?

Topography (variation in elevation)
also affects the physical
environment.
As you go up a mountain, air
temperature drops by about 1°C for
each 220 m of elevation because
rising air expands and cools
adiabatically.
When prevailing winds bump into
mountain ranges, the air rises, cools,
and releases moisture. The now-dry
air descends on the leeward side,
creating a rain shadow.
Which term refers
to variation in the
elevation of Earth’s
surface?

Figure 41.8 A Rain Shadow
It tends to rain
more in the
mountains
than in
adjacent
lowlands -
why?

Topography also influences aquatic
environments:
• Flow velocity depends on slope.
• Water depth determines gradients of many
abiotic factors, including temperature,
pressure, light penetration, and water
movement.

Climate diagram—
superimposed graphs of
average monthly
temperature and
precipitation over a year.
The axes are scaled so that
it is easy to see the
growing season:
• When temperatures are
above freezing and the
precipitation line is
above the temperature
line

Figure 41.9 Climate Diagrams Summarize Climate in an Ecologically Relevant Way

Apply the Concept, page 853
1. Which locality is near
the equator?
2. Which locality has the
greatest seasonality in
temperature?
3. Which locality has the
longest growing
season?
4. Which locality is in
the Northern
Hemisphere?

Concept 41.3 Biogeography Reflects Physical Geography
An organism’s physiology, morphology, and behavior
affect how well it can tolerate a particular physical
environment.
Thus, the physical environment greatly influences what
species can live there.
We expect species that occur in similar environments to
have evolved similar phenotypic adaptations.

Early scientist–explorers began to understand
how the distribution of Earth’s physical
environments shapes the distribution of
organisms.
Their observations revealed a convergence in
characteristics of vegetation found in similar
climates around the world.

Biome—a distinct physical environment inhabited by
ecologically similar organisms with similar
adaptations.
Species in the same biome in geographically separate
regions display convergent evolution of
morphological, physiological, or behavioral traits.
• Climate
• Soil
• Plants
• Animals
• Interacting landscapes

Terrestrial biomes are
distinguished by their
characteristic vegetation.
Distribution of terrestrial biomes
is broadly determined by
annual patterns of
temperature and
precipitation.
• These factors vary along
both latitudinal and
elevational gradients.
-Different terrestrial biomes are
typically distinguished primarily
by their?

Figure 41.10 Terrestrial Biomes Reflect Average Annual Temperature and Precipitation
-Which factor is the
most important
criterion for
determining the
different types of
tropical biomes?
-If, over a long period
of time, a region that
is currently in the
subtropical desert
biome receives
substantially more
rainfall, this region
will most likely
become what?

Figure 41.11 Global Terrestrial Biomes
Terrestrial biomes are often named for major
physical or climatic factors and for their
predominant vegetation.
-In which country would you most likely find the boreal forest
biome?
-In which biome is most of Massachusetts located? Mississippi?

Other factors, especially soil characteristics, interact
with climate to influence vegetation.
• Example: Southwestern Australia has
Mediterranean climate with hot, dry summers and
cool, moist winters. The vegetation is
woodland/shrubland, with no succulent plants.
 The soils are nutrient-poor, and there are
frequent fires. Succulents are easily killed by
fires.

Grasslands normally occur where there is not
enough precipitation to support forests, but is
more plentiful than is typical of deserts.
But some grasslands occur in unexpected
places, demonstrating that biome boundaries
are not perfectly predicted by temperature and
precipitation—other factors also affect the
vegetation.

Figure 41.12 Similar Vegetation Types, Different Conditions

Fire is a significant factor affecting vegetation.
Fire rarely kills grasses but often kills shrubs
and trees; fires help maintain grasslands.
Humans have probably used fires for millennia
to manipulate their environment and maintain
grasslands.
A region of Europe has moderately high rainfall and mild
temperatures, but it also has a history of periodic fires. What
vegetation would you most likely expect to see there?

Aquatic Biomes
The biome concept is also applied to aquatic
environments.
Aquatic biomes are determined by physical factors
such as water depth and current, temperature,
pressure, salinity, and substrate characteristics.
Aquatic biomes account for the largest part of the
biosphere in terms of area.
• Oceans cover about 75% of the earth's surface
and have an enormous impact on the biosphere

30°N
Tropic of
Cancer
Equator
30°S
Continental
shelf
Lakes
Coral reefs
Rivers
Oceanic pelagic
zone
Estuaries
Intertidal zone
Abyssal zone
(below oceanic
pelagic zone)
Key
Tropic of
Capricorn

The primary distinction for aquatic biomes is salinity:
freshwater, saltwater, and estuarine biomes.
An estuary is an area where freshwater and saltwater
meet.
Salinity determines what species can live in the biome,
depending on their ability to osmoregulate.
-Aquatic biomes are distinguished primarily by what?
-Where would you most likely find salinity levels varying
considerably over space and time?

In streams, current velocity is important.
Organisms must have adaptations to
withstand flow.
Current also impacts the substrate—whether
rocky, sandy, silty, etc. Substrate also
determines what species are present.

Lakes and oceans are divided into water-depth
zones.
Nearshore regions (littoral or intertidal) are
shallow, impacted by waves and fluctuating
water levels. Distinct zonation of species is
common.
Photic zone—depth to which light penetrates;
photosynthetic organisms are restricted to this
zone

In the open-water limnetic zone of lakes and
the pelagic zone of oceans beyond the
continental shelf, the prominent
photosynthesizers are phytoplankton (free-
floating photosynthetic organisms).
The phytoplankton of the oceans are analogous to the
grasses of the grassland biome because both types of life
are what?

Figure 41.13 Water-Depth Zones (Part 1)

Figure 41.13 Water-Depth Zones (Part 2)
Rank the depth
zones in terms of
their proximity
to the surface of
an ocean (from
closest to
farthest away)?

The aphotic zone is too deep for light penetration and
so is sparsely populated.
Benthic zone—lake or ocean bottom
Organisms in the deepest oceans (abyssal zone) must
have adaptations to deal with high pressure, low
oxygen, and cold temperatures.

Concept 41.4 Biogeography Also Reflects Geological History
Alfred Russel Wallace advanced the idea of natural
selection along with Darwin.
Wallace studied species distributions in the Malay
Archipelago and observed dramatically different
bird faunas on two neighboring islands, Bali and
Lombok.
The differences could not be explained by soil or
climate.

He suggested that the deep channel between the
islands would have remained full of water (and a
barrier to movement of terrestrial animals) during
the Pleistocene glaciations when sea level
dropped.
Thus, the faunas on either side of the channel
evolved mostly in isolation over a long period of
time.

Wallace’s observations led him to
divide the world into six
biogeographic regions.
Each region encompasses multiple
biomes and contains a distinct
assemblage of species, many of
which are phylogenetically
related.
Many of the boundaries
correspond to geographic
barriers to movement: bodies of
water, deserts, mountain ranges.
What causes
biogeographic
regions?

Figure 41.14 Earth’s Terrestrial Biogeographic Regions
-Wallace’s line in the Malay Archipelago separates the _______ and
the _______ biogeographical regions.
-The continental United States is in the _______ biogeographic
region.

Boundaries of some biogeographic
regions are related to continental
drift.
• Example: Southern beeches
(Nothofagus) are found in
South America, New Zealand,
Australia, and some south
Pacific islands.
 The genus originated on the
supercontinent Gondwana
during the Cretaceous and
was carried along when
Gondwana broke apart.

Figure 41.15 Distribution of Nothofagus (Part 2)

The biogeographic regions occupy land masses that
have been isolated from one another long enough to
allow the organisms to undergo independent
evolutionary radiations.
The biotas developed in isolation throughout the Tertiary
(65 to 2.6 mya), when extensive radiations of flowering
plants and vertebrates took place.

Continental movement can also eliminate
barriers, allowing biotic interchange.
• Examples: when India collided with Asia
about 45 mya; when a land bridge formed
between North and South America about 6
mya.
- The collision of India and the rest of Asia occurred about
_______ million years ago and led to the formation of the
_______ biogeographic zone.
-Australia will likely slam into Asia many million years in the
future. The most likely consequence of this fusion will be a?

Biogeographers use phylogenetic information,
the fossil record, and geological history to
study modern distributions of species.
Geographic areas are superimposed on
phylogenetic trees. The sequence and timing
of splits in the phylogenetic tree are compared
with sequence and timing of geographic
separations or connections.

Apply the Concept, page 860
1. Which one node
(split) in the tree
most clearly
responds to an event
of continental
separation?
2. Are there groups
of mammals that
appear to have
dispersed to new
areas following
removal of a barrier
to disperal?

Concept 41.5 Human Activities Affect Ecological Systems
on a Global Scale
Human activities are altering ecological
systems on a global scale.
Some have suggested we are entering a new
geological period, the “Anthropocene” or Age
of Humans.
We are changing the distributions of organisms,
vegetation, and topography, as well as Earth’s
climate.

on a Global Scale
Others suggest the new age should be called
the “Homogenocene,” or Homogeneous Age,
because the net effect of our activities is to
make ecological systems less complex and
more uniform.

on a Global Scale
When we use natural ecosystems for hunting,
fishing, grazing, or logging, we remove
particular species and change their
abundances.
If we remove too many, we can even cause
some species to go extinct.
This can change the patterns of interaction
among species, and thereby change how
entire ecosystems function.

on a Global Scale
Human-dominated ecosystems, such as
croplands, pasturelands, and urban
settlements now cover about half of Earth’s
land area.
These ecosystems have fewer interacting
species and are less complex.

on a Global Scale
In agricultural lands,
monocultures replace
species-rich natural
communities.
Diversity of crops planted is
also very low: 19 crops
comprise 95% of total
global food production.
Agricultural systems are
more spatially and
physically uniform than
natural ecological systems.

Figure 41.16 Human Agricultural Practices Produce a Uniform Landscape
1. Predict hat
biome do you
think this
soybean field is
located in?
2. Deduce how
the ecological
systems in this
biome have been
manipulated to
make soybean
fields.
3. Infer the type of natural capital that exisists in this biome that make
them productive farmland.
4. Predict the downsides to converting forest ecological systems to grain
or legume agriculture.

on a Global Scale
Human activities also reduce complexity in natural
ecosystems:
• Damming and channelization of rivers
• Pollution and habitat fragmentation
• Overexploitation of wild species
• Introductions of new species
-Rank the following from most to least in terms of land
they use: cities, pasture for livestock, and agriculture.

on a Global Scale
Humans move species throughout the globe,
sometimes deliberately, sometimes
inadvertently.
Human-assisted biotic interchange is
homogenizing the biota of the planet, blurring
the spatial heterogeneity in species
composition that evolved during long periods
of continental isolation.

on a Global Scale
New subdisciplines of ecology address how we
can preserve ecological systems and their
ability to sustain life on our planet.
Conservation ecology seeks to understand
the process of extinction and ways to prevent
extinction of vulnerable species.
Restoration ecology seeks to restore the
health of damaged ecosystems.

on a Global Scale
Natural systems are sometimes altered so
strongly that extinction will occur unless the
systems are restored.

on a Global Scale
Natural history—observation of nature outside of a
formal, hypothesis-testing investigation—provides
important knowledge about ecosystems
• These observations are often the source of new
questions and hypotheses and aid in design of
ecological experiments.
-The observation of nature that is conducted outside of a formal,
hypothesis-testing investigation is called?
-A biologist is observing the movement patterns of robins in a
meadow and recording data about these observations, rather
than testing a particular hypothesis about the birds.
This scientist would be best described as engaged in the study of
what?

on a Global Scale
Mathematical models and computer simulations
are often needed to study the complexities of
ecological systems.
They must be based on natural history
knowledge of the system.

Answer to Opening Question
The Borderlands are arid—they are at 32° N, where the
warm, dry air of the Hadley cells descends.
Other grasslands around the world occupy different
physical environments, and have different histories.
Why grasslands of the Borderlands have not recovered
from overgrazing may be due to many factors:
Can basic ecological principles suggest why
removing cattle has not restored grasses
to the Borderlands?

Answer to Opening Question
• Periodic burning may be needed.
• It may be necessary to restore the original
landscape, to return water and nutrients to
the soil that grasses require.
• Interaction between fire and nutrients may
influence which vegetation type will be
favored.
• It may be necessary to remove the existing
shrubs before other measures will have a
chance of success.

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