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54
Ecology and the
Distribution of Life
•
Ecology
• The scientific study of interactions between
organisms and their environment.
•
It is a relatively new branch of science,
with roots in Darwin’s The Origin of
Species.
As Haeckel explained:
“Ecology is the study of all those complex
interrelations referred to by Darwin as
‘the conditions of the struggle for
existence.’”
Why Study Ecology?
•
Human activities can profoundly affect
our environment
• We need data on the consequences of our
activities.
•
Ecological understanding improves:
• our ability to grow food sustainably
• managing pests and diseases
• dealing with natural disasters
• avoiding unintended consequences for ourselves
and other organisms
“Ecology” is not equivalent to
“environmentalism.”
 Ecology is a science that generates
knowledge about interactions in the
natural world.
 Environmentalism is the use of this
knowledge (with economics, ethics, etc.),
to inform personal decisions and public
policy relating to stewardship of natural
resources and ecosystems.

•
Ecology encompasses 2 components:
• Biotic – living
• Abiotic - Nonliving
•
New Tools to study Ecology:
• mathematical models
• molecular techniques
• satellite imaging
Weather and Climate
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•
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Weather is the short-term state of
atmospheric conditions at a particular
place and time.
Climate refers to average atmospheric
conditions, over a longer time.
“Climate is what you expect, weather is
what you get!”
Organisms and their Climate
Organism responses to climate tend to be
adaptations that affect physiology,
morphology, and behavior.
These adaptations are among the forces
driving speciation over evolutionary
time.
Why do Climates Vary?
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Differences in solar energy
•
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Temperature decreases with elevation
Movement of air
• Due to angle of sun’s rays
• Tilt of Earth on axis
• Warm air rises (i.e. at the equator)
• The air cools and is no longer able to hold
moisture
• precipitation
• As it descends, the cool air starts to warm and
take up moisture
• Look at figure at where air is descending – this is
where we find the Earth’s deserts
• This results in global air circulation and
prevailing winds
Figure 54.2 Air Circulation in Earth’s Atmosphere
•
Rotation of Earth
influences the
movement of air masses
produced by global air
circulation
• Results in prevailing
winds
• Deflected to right
in Northern
Hemisphere
• Left in Southern
Hemisphere
Global air circulation is what drives ocean
currents
Organisms and their environment
•
Organisms must adapt to climatic
challenges
• Metabolic specializations
• Behavioral specializations
Adaptations of organisms
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Organisms may produce antifreezes to
deal with low temps
• Limits damage to cells
•
Rounded shapes and short appendages
to reduce surface area
• Reduce heat loss
•
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Pigmentation
Behavioral changes
• “sunning”, looking for shelter
• Migration to new area
Biome
•
Biome
• An environment defined by its climatic and
geographic attributes
• characterized by its dominant plants.
• provide three- dimensional structure
• modify microclimates near the ground
• strongly influence other organisms living there.
Figure 54.5 The Global Distribution of Biomes
Biome
•
•
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General descriptions of the biomes
cannot describe all the variation
existing in each.
Boundaries between biomes are
somewhat arbitrary; in many places
biomes merge into one another.
Recognizing the major biomes is useful
because these environments share
ecological attributes irrespective of
their location.
Tundra:
• Location:
• Arctic
• high elevations
•
•
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Vegetation is low-growing perennials.
permafrost
Animals migrate or go dormant for
much of the year.
Boreal forest (taiga):
Long, cold winters; short
summers
• Dominated by evergreens in
the Northern Hemisphere—
can start photosynthesis
quickly in the short growing
season.
• Only a few tree species
• Dominant mammals, (e.g.,
moose and hares) eat leaves.
•
Temperate evergreen forests:
• Location:
• Along coasts of continents at mid to high
latitudes.
•
Winters are mild but wet; summers
are cool and dry.
Temperate deciduous
forest:
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•
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Precipitation is distributed
evenly, but temperatures
fluctuate dramatically.
Dominated by deciduous
trees that lose leaves during
the cold season.
Some animals migrate to
avoid cold season (e.g.,
songbirds), others hibernate
Temperate grasslands:
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Dry much of the year; hot
summers and cold winters.
Rich in species; grasses, sedges,
and forbs. Plants are adapted to
grazing and fire.
Much of this biome has been
converted to agriculture. The
topsoil is deep and rich.
Hot desert:
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In two belts at 30°N and
30°S
More species and more
structurally diverse
vegetation than cold deserts.
Plants have many adaptations
to dry conditions. Succulents
are common. Many annuals
grow only after a rainfall.
Small animals stay in burrows
during the day; many get
water only from their food.
Cold desert:
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In continental interiors and rain
shadows.
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Dominated by few species—lowlying shrubs. Plant growth mostly
occurs in spring.
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Plants produce lots of seed that
supports seed-eating birds and
rodents.
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Animals burrow to escape cold
temperatures.
Chaparral:
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On western sides of continents
with cool ocean currents
offshore.
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Winters are cool and wet,
summers warm and dry.
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Adapted to fire.
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Shrubs and low trees with tough,
evergreen leaves
Thorn forest and tropical
savanna:
At latitudes below the hot
deserts
• Little rain in winter; but may be
heavy in summer.
• Small trees may drop leaves in
dry winter
• Savannas—grasslands with
scattered trees; supports large
grazing and browsing mammals
and large predators.
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Tropical deciduous
forest:
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•
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Most trees lose leaves
during the dry season; many
flower while they are still
leafless.
Most of the plants are
pollinated by animals, and
are important “refueling”
stops for migratory birds.
Most have been cleared for
agriculture and cattle
grazing.
Tropical evergreen
forest (rainforest):
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Equatorial regions with
high rainfall.
Highest species richness
of all biomes. Up to 500
tree species per km2.
Also highest overall
productivity. Most
nutrients are tied up in
vegetation; soils are poor.

Florida
 Combination of biomes – unique areas
○ Temperate deciduous forest
○ Tropical deciduous forest
○ Aquatic biomes
 Everglades unique area
Biogeographic Regions
Evolutionary history is influenced by
geological history
•
Alfred Russel Wallace – 1800s
• traveled extensively in the Malay
Archipelago
• noticed remarkable patterns of distribution
of organisms
• striking differences in biota from one island to
the next that could not be explained by
differences in geology or climate - the islands
were identical
•
drew a line through the archipelago based on
distributions of plants and animals
• He deduced that the differences had to do with the depth
of water separating the two regions
• It remained a barrier even during Pleistocene glaciations
when sea level dropped more than 100 m.
Biogeographic Regions
•
Earth can be divided into biogeographic
regions, each containing characteristic
species assemblages.
• Boundaries occur where species composition
changes dramatically over short distances.
• The regions have barriers to dispersal
between
• Mountains
• oceans, etc.
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A species found only in a certain region
is said to be endemic to that region.
• Remote islands tend to have endemic biotas
because water greatly restricts dispersal.
• Madagascar has many endemic species.
• Biodiversity hotspot
Biogeographic Regions
Causes of the distribution of species were
only speculated upon until two scientific
advances occurred:
 Acceptance of the theory of continental
drift
 Development of phylogenetic taxonomy
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About 280 million years ago, the
continents were united into one land
mass
• Pangea
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During the Triassic period, the
supercontinent Pangaea broke apart.
Many groups of terrestrial and
freshwater organisms had already
evolved.
Geologic events can also bring land
masses together.
Land bridges can form, for instance,
when ocean levels drop
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A vicariant event
• Appearance of a physical barrier that splits
the range of a species
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Dispersal
• if organisms cross an existing barrier and
establish a population
•
Both result in discontinuous ranges.
• Studies can show which once caused an
observed distribution
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Human activity is another force
capable of generating unusual
distribution patterns
• Many species have been introduced to new
regions; some have been deliberate, some not
• Many introductions have resulted in
disaster—diseases of crops and animals,
household pests, etc.
Ocean
~70% surface of the Earth is covered
by ocean
 Contains as much as 99% of the
biosphere!
 There is MUCH we still do not know
about the ocean

○ What will be our impact on it?
Ocean Life Zones
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Ranges of marine organisms are
restricted by water temperature,
salinity, and food supply, which all
vary spatially.
• Oceans can be divided into distinct “life
zones.”
• They are identified mainly in relation to
water depth and light penetration.
Ocean
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Photic zone
• enough light to support photosynthesis
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Coastal zone
• extends from the shoreline to the edge of the
continental shelf
• characterized by shallow, well-oxygenated water
and stable temperatures and salinities
• Littoral Zone – affected by wave action
• Intertidal Zone – affected by the tides
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Pelagic Zone
• Open ocean
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Benthic Zone
• Ocean sediment
Figure 54.14 Oceanic Life Zones
Ocean
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Dominant Autotrophs
• Phytoplankton – photosynthetic protists
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In the open ocean, or pelagic zone, the
principal consumers are zooplankton—
mainly small crustaceans and larval
stages of marine animals.
Ocean
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Aphotic Zone
• Depths reached by less than 1 percent of
incoming sunlight
• Organisms in this region subsist on decaying
organic matter that sinks down from the
photic zone
• Some produce their own light in
bioluminescent organs
• In deep-ocean trenches and rift valleys,
ecosystems are often sustained by
chemosynthetic microbes
• can metabolize the nutrients in seawater without
the aid of sunlight
• “chemosynthesis” in hydrothermal vents
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Freshwater environments
• running water (streams and rivers)
• standing water (lakes and ponds)
Lakes can be divided into life zones
similar to those in the oceans
• Although freshwater environments
cover less than 3% of Earth’s surface
they are home to about 10% of all
aquatic species
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Most animals that live in fresh water
cannot survive in ocean water, which can
limit dispersal.
Most freshwater fish species are
restricted to one continent because
they can’t tolerate salt water (can’t
disperse).
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Estuaries form where rivers meet the
ocean, and salt water mixes with fresh
water
• They have many unique species
• play an important role for other species as a
conduit between marine and freshwater
environments
• Ocean’s “nurseries”