Contents
‣
‣
1) Biomes
‣
Distribution of biomes
Carbon cycle
Classification of biomes
Nitrogen cycle
Phosphorus cycle
2) Components of Ecosystems
Sulfur cycle
Components of ecosystems
Water cycle
Factors affecting ecosystems
Habitats
Adaptations
‣
4) Biogeochemical Cycles
3) Energy flow in Ecosystems
Trophic structure
Energy in ecosystems
Ecosystem productivity
Ecological pyramids
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‣
5) Ecosystem Stability
Environmental change
Key species
Ecological succession
Ecology
CO
2
O
2
‣ Ecology is the study of the
relationships between
organisms and their physical
and biotic environment:
Relationships involve
interactions with the physical
world as well as
interrelationships with other
species and individuals of the
same species.
Nutrients
Biological Complexity
‣
‣
Living organisms can be
studied at different levels of
complexity.
From least to most complex,
these levels are (in an
ecological context):
Individual
Biosphere
Biome
Ecosystem
Community
Population
Community
Population
Ecosystem
Biome
Biosphere
Individual
The Biosphere
• The biosphere is
the region within which
all living things are found on Earth.
• It is the narrow belt around the Earth extending from
the bottom of the oceans to the upper atmosphere.
Image: NASA
Exploring the
Biosphere
• Our knowledge of what
constitutes the biosphere
continues to develop as
scientists continue their
exploration of the Earth.
• The biosphere extends
into the Earth’s crust,
below the oceans and
deep into rock fissures; it
extends well into the
Earth’s
upper atmosphere.
Life exists in all places, from blind white crabs
in lightless environments...
to tube worms in the crushing ocean depths.
Biomes
• The biosphere encompasses
all living things on Earth.
It comprises a number of
aquatic and terrestrial
biomes.
• Biomes are the largest
geographically based biotic
communities that can be
conveniently recognized.
• Biomes within the same
category have specific,
characteristic features.
Desert biome
Terrestrial Biomes
• Terrestrial biomes are recognized for all the major
climatic regions of the world and are classified on the
basis of their predominant vegetation type.
The same biome may occur in widely separated regions.
Biomes and Weather Cells
• Three air cells circle each hemisphere of the Earth.
The interaction of these cells is a major contributor the formation of biomes.
Rising air allows
cloud formation in
temperate regions
Air rising at the
equator causes the
formation of rain
clouds
After losing its
moisture, dry air
descends
Dry air descends
at the poles
Hadley
cell
Polar
Temperate
Desert
Tropical
Ferrel
cell
Desert
Polar
cell
Temperate
Polar
Hot Deserts
• Deserts are arid regions (annual rainfall generally less than 25 cm). The
hot desert biome is found in two belts, centered at 30° latitude north
and south of the Equator.
• Hot deserts receive most of their rainfall in summer. The driest regions
are in central Australia and the middle of the Sahara Desert.
The temperature range is approximately 30°C, and the winter and summer
are both very warm.
Ayres Rock, Australia
Sand dunes, Namibia
Physical Factors:
Hot Deserts
Example: Khartoum, Sudan 15.5°N
Temperature range: 9°C
The winter and summer are
both very warm.
Annual total rainfall: 15 cm
Khartoum
Cold Deserts
• The cold desert biome is found in dry regions in the mid to high latitudes,
especially in the interiors of large continents. Cold deserts also occur at
high altitudes in the rain shadows of mountain ranges.
• Cold deserts receive most of their small amount of rainfall in winter.
Sierra Nevada, USA
Arches National Park, USA
Physical Factors:
Cold Deserts
Example: Cheyenne, Wyoming 41°N
Temperature range: 23°C
The winters are cold; summers
are much warmer.
Annual total rainfall: 38 cm
Cheyenne
Savanna & Thorn Forests
‣ Tropical savannas are found in central and eastern
Africa, and in tropical and subtropical regions of
South America and Australia. Thorn forests are
found on the equatorial sides of hot deserts.
• Both have mild, dry winters and mild, wet summers.
Unlike savanna, thorn forests generally lack grasses.
This reflects the increased aridity of the climate.
Physical Factors:
Savannas
Example: Kayes, Mali 14°N
Temperature range: 10.7°C
Annual total rainfall: 74 cm
Kayes
Tropical Rainforests
• Tropical evergreen forests
are found in equatorial
regions where total annual
rainfall exceeds 250 cm and
the dry season lasts for no
more than 2-3 months.
These forests are speciesrich.
• The climate is warm and
rainy all year round.
Rainforest, Central America
Physical Factors:
Tropical Rainforests
Example: Iquitos, Peru 3°S
Temperature range: 2.2°C
Annual total rainfall: 262 cm
Iquitos
Temperate Forests
Temperate deciduous forest
• Temperate forests occur
throughout mid latitudes
where there is a high annual
rainfall.
• Temperate forests are usually
deciduous, but where seasonal
fluctuations are moderated by
proximity to the coast, the
forests are evergreen and are
termed temperate rainforests.
Temperate rainforest
Temperate rainforests occur in
south-eastern Australia, New
Zealand, along the Pacific
North-West coast of the
United States.
Physical Factors:
Temperate Forests
Example: Madison, Wisconsin 43°N
Temperature range: 31°C
The temperature fluctuates dramatically
between summer and winter.
Total annual rainfall: 81 cm
Ample falls throughout the year.
Madison
Temperate Grasslands
• Temperate grasslands or
prairies occur in mid
latitudes, in regions that are
relatively dry for much of the
year. They occur in many parts
of the world, and include:
The Pampas of Argentina
The South African veldt
The Great Plains of the USA
• Grasslands are highly
productive and large regions
have been converted to
agriculture.
Physical Factors:
Temperate Grasslands
Example: Pueblo, Colorado 38°N
Temperature range: 24°C
The temperature fluctuates widely, with hot summers,
cold winters.
In some grasslands, most precipitation occurs in
the winter. In others, the majority falls in summer.
Total annual rainfall: 31 cm
Pueblo
Tundra
• The tundra biome is found
in the Arctic and high in
the mountains at all
latitudes. It is dominated
by low-growing perennial
plants.
Tundra: northern Canada
The Arctic tundra is very
wet even though rainfall
is low and this is because
the water cannot drain
down through the
permafrost (permanently
frozen ground).
Arctic tundra
Physical Factors:
Tundra
Example: Greenland
73°N
Temperature range: 28°C
Total annual rainfall: 23 cm
Greenland
Mountains
and Ice
• Mountainous regions are
associated with their own
altitude adapted vegetation.
• The icy regions of the polar
ice caps (the Arctic and
Antarctic) form sheets of ice
that extend into and over the
sea.
Predicting Biome Distribution 1
• Temperature and precipitation are excellent predictors of biome
distribution. Temperature decreases from the equator to the poles.
Latitudinal regions
Polar
Arctic
region
Subarctic
region
Temperate
region
Tropical
region
Equatorial
Annual precipitation (mm)
Predicting Biome Distribution 2
•
Temperature and precipitation act together as limiting factors to determine the type of desert, grassland, or forest biome in a region.
Components of an Ecosystem
Physical
environment
Community
• A biome is a large geographical region
comprising natural units called ecosystems.
• An ecosystem encompasses the physical
environment and the community.
Ecosystem
Physical
environment
Abiotic factors
atmosphere
soil
water
wind speed
wind direction
current velocity
Community
Biotic factors
competitors
symbionts
predators
parasites
pathogens
Ecosystems
Light intensity varies
Fast flowing water habitat
Still water habitat
• An ecosystem includes:
all of the organisms
(the community) …
and their physical
environment.
• There are many
different sorts of
ecosystems from
natural to artificial, and
they range in size from
large to small.
Rock habitat
Stream bank habitat
Flow rate varies
Rainfall level varies
Communities
• A community is a naturally occurring group of
organisms living together as an ecological
entity; the biological part of the ecosystem.
A nudibranch snail
feeding on rock
encrusting organisms
Environments
• The physical
environment
refers to the
physical
surroundings of
any organism,
including:
the medium, e.g.
water
substrate, e.g. soil
climatic
(atmospheric)
conditions
light …
and other physical
properties.
Climate and
Vegetation
• The type and
extent of
vegetation in a
particular
ecosystem is
determined by
physical factors on
both a large scale
and on a very
localized
(microclimate)
level.
Vegetation
patterns are
governed largely
by climate (which
High latitude climate
Temperate climate
Factors Affecting Ecosystems
‣ Abiotic (physical)
factors are the
influences of the
non-living parts of
the ecosystem.
Examples include
pH, salinity,
temperature,
turbidity, wind
speed and
direction, humidity,
precipitation, water
pressure, and light
intensity and
quality.
‣ Biotic factors are
the influences of
the living parts of
the ecosystem.
Monitoring Physical Factors
Devices for measuring the physical
factors in the field include the
following meters:
Quantum light meter
Dissolved oxygen
Oxygen meter
pH meter
Total dissolved solids (TDS) meter
Current meter
Multi-purpose meter
Photo: Courtesy PASCO scientific
•
Hygrometer
Wind meter
Other equipment includes:
Secchi discs
Nansen bottles
Pasco datalogger with attached sensor
Physical Gradients
‣ Gradients in abiotic
factors are found in
almost every
environment.
They influence habitats
and microclimates, and
determine patterns of
species distribution.
• The effects of these
physical (or
environmental)
gradients are
particularly evident
where physical
conditions change
markedly within a
short distance, e.g. in
Desert Environments
‣ Desert environments experience extremes
in temperature and humidity, but they are
not uniform with respect to these factors.
Physical conditions vary widely within the one
general environment. Crevices, burrows, and
the presence of rock overhangs and
vegetation create microclimates where
extremes in physical conditions are reduced
compared to the desert surface.
Desert Factors
300 m altitude
27°C, 20% humidity
Hypothetical values for temperature (°C) and percentage
humidity at midday in a desert environment.
1 m above
ground
33°C, 20% humidity
Desert surface
45°C, <20% humidity
Burrow
Crack/crevice
Under rock
28°C, 60% humidity
(1 m underground)
27°C, 95% humidity
(2 m underground)
25°C, 95% humidity
Rocky Shore Environments
•
Rocky shore environments typically exhibit marked physical gradients as a result
of tidal movements. Horizontal and vertical gradients in salinity, temperature,
dissolved oxygen, and exposure time are reflected in the communities found at
different positions on the shore.
Horizontal: from the low tide to the high tide marks
Vertical: from the bottom to top surfaces of rocks and boulders.
Rocky Shore Factors
Hypothetical values for physical
factors in rock pools at different
places on a rocky shore.
Salin:
Temp:
DO:
Exp:
salinity
temperature
dissolved oxygen
exposure time
(per 12 hour tidal cycle)
Salin:
42
-1
gl
Temp:
28° C
DO: 20%
Salin:
39
-1
gl
Temp:
28° C
DO: 30%
Salin:
38.5 gl
Temp:
26° C
DO: 42%
Exp: 8 h
-1
-1
-1
-1
Salin:
37 gl Salin:
36 gl Salin:
35 glTemp:
22° C Temp:
19° C Temp:
17° C
DO: 57%
DO: 74%
DO: 100%
Exp: 6 h
Exp: 4 h
Exp: 0 h
A Tropical Rainforest
• The high species
diversity of
tropical
rainforests can
be supported
because of the
wide variety of
microhabitats
provided by the
layered structure
of the forest.
• The physical
conditions at the
uppermost level
are quite
different to those
at the forest floor
Canopy
Subcanopy
Understorey
Ground layer
Light: light intensity
Wind: wind speed
Hum: humidity
Rainforest Factors
Light: 70%
Wind: 15 kmh-1
Hum: 67%
Light: 50%
Wind: 12 kmh-1
Hum: 75%
Light: 12%
Wind: 9 kmh-1
Hum: 80%
Light: 6%
Wind: 5 kmh-1
Hum: 85%
Light: 1%
Wind: 3 kmh-1
Hum: 90%
Light: 0%
Wind: 0 kmh-1
Hum: 98%
Oxbow Lakes in Summer
‣ Oxbow lakes are formed from old
river meanders that have been cut
off and become isolated from the
main channel following the change
in the river’s course.
Occasionally they may be deep
enough to develop temporary, but
relatively stable, gradients in physical
factors from the surface to the
bottom of the lake.
Oxbow Lake Factors
Zone of mixing
Temp: 22.1°C
Oxy: 9.7 mgl-1
Light: 25%
Temp: 13°C
Oxy: 3.4 mgl-1
Light: 5%
Temp: 24.6°C
Oxy: 9.2 mgl-1
Light: 100%
Temp: 16°C
Oxy: 5.2 mgl-1
Light: 10%
Temp: 12.5°C
Oxy: 0.2 mgl-1
Light: 2.5%
Ecological Niche
• The ecological
niche describes
the functional
position of an
organism
in its
environment.
• A niche
comprises:
the habitat in
which the
organism lives.
the organism’s
activity
pattern: the
periods of
time during
Adaptations
Habitat
Activity
patterns
Presence of
other organisms
Physical
conditions
The Fundamental Niche
• The fundamental
niche of an organism
is described by the full
range of
environmental
conditions (biological
and physical) under
which the organism
can exist.
• The realized niche of
the organism is the
niche that is actually
occupied. It is
narrower than the
fundamental niche.
This contraction of the
realized niche is a
Physical Conditions
• The physical conditions influence the
habitat in which an organism lives.
These include:
substrate
humidity
sunlight
temperature
salinity
pH (acidity)
exposure
altitude
depth
• Each abiotic (or physical) factor may be
well suited to the organism or it may
present it with problems to overcome.
Law of Tolerance
• The law of tolerance states that “For each
abiotic factor, an organism has a range of
tolerances within which
it can survive.”
Tolerance range
Number of organisms
Optimum range
Unavailable
niche
Examples of abiotic
factors that influence
size of the realized niche
Marginal
niche
Too
acidic
Too cold
Preferred
niche
Marginal
niche
pH
Temperature
Unavailable
niche
Too alkaline
Too hot
Habitat
• An organism’s habitat is the physical
place or environment in which it lives.
• Organisms show a preference for a
particular habitat type, but some are
more specific in their requirements than
others.
Lichens are found on rocks, trees, and
bare ground.
Most frogs, like this leopard frog, live
in or near fresh water, but a few can
survive in arid habitats.
Habitat Range
• An organism’s habitat is not always of a single
type. Some organisms occupy a range of
habitats. There are various reasons why:
Highly adaptable in habitat requirements.
Different, but equivalent, resources available in
different habitats.
Reduced competition for resources in sub-optimal
habitats.
• Habitat extremes may influence growth form,
especially in plants.
Habitat Preference
• Organisms may select
particular areas
within their general
habitat, even in
apparently
homogeneous
environments, such
as water.
This is termed habitat
preference.
Example: Aquatic
organisms may show
a preference for a
particular substrate
type, water depth or
velocity, water clarity,
or degree of
vegetation cover or
habitat disturbance.
Damselfly nymph
Rainbow trout
Resources in a Habitat
• The habitat
provides organisms
with the following
resources:
Food and water
sources
Mating sites
Nesting sites
Predator avoidance
Shelter from climatic
extremes
• However, the
organism may or
may not have the
adaptations to
exploit all the