ECOSYSTEMS
SL
Chapter B, C & D
Contents
B 4.1 adaptation to
environment– 3h
B 4.2 ecological
niches – 4h
C 4.2 transfers of
energy and
matter– 5h
C 4.1 populations
and communities–
5h
D 4.2 stability and
change – 4h
D 4.3 climate
change – 3h
D 4.3.1
人为的
• Anthropogenic causes of climate change
• Limit to anthropogenic increases in atmospheric concentrations of
carbon dioxide and methane.
1. Anthropogenic causes of climate change
 Greenhouse effect: The ability of greenhouse
gases to absorb longwave radiation has the
overall effect of retaining heat in the Earth’s
atmosphere.
 The incoming radiation from the sun is short
wave ultraviolet and visible radiation.
 Some of this radiation is absorbed by earth’s
atmosphere
 The warmed Earth emits longer wavelength
radiation (heat)
1. Anthropogenic causes of climate change
 Longer wave radiation (infrared radiation)
is absorbed by greenhouse gases that
retain the heat in atmosphere.
 The greenhouse gases also re-emits it back
towards the Earth.
 This causes the greenhouse effect and
results in an increase in atmospheric
temperature
 Greenhouse effect is a natural
phenomenon but not its increase.
1. Anthropogenic causes of climate change
 Greenhouse gases have the
ability to absorb and radiate
infrared radiation (heat).
 Carbon dioxide and methane
are greenhouse gases. They
have increased by human
activity (anthropogenic).
1. Anthropogenic causes of climate change
 Carbon dioxide is produced by combustion
of fossil fuels.
 Natural stores of carbon are damaged or
destroyed by human activities, like
deforestation.
 Methane is released from the guts of
ruminant mammals, such as cattle, that
are farmed by humans.
 Anaerobic bacteria in waterlogged rice
paddy fields release methane
1. Anthropogenic causes of climate change
 Climate refers to the patterns of temperature and precipitation that occur
over long periods of time.
 The Earth’s temperature has fluctuated naturally.
 There is a very striking correlation between carbon dioxide concentration
and global temperatures.
D 4.3.2
• Positive feedback cycles in global warming
• Include release of carbon dioxide from deep ocean, increases in
absorption of solar radiation due to loss of reflective snow and ice,
accelerating rates of decomposition of peat and previously
undecomposed organic matter in permafrost, release of methane from
melting permafrost and increases in droughts and forest fires.
2. Positive feedback cycles in global warming
 Positive feedback loops occur when the output of a process feeds back into the
system in a way that moves the system increasingly away from the average state
 Global warming has a positive feedback effect on the earth and its atmosphere
 This means that global warming leads to more global warming, which further
increases global warming
2. Positive feedback cycles in global warming
 release of carbon dioxide from deep
ocean
 Surface water are warmer →
phytoplankton produce more biomass
→ biomass can be passed on to the
rest of the food chain → when
organisms die, more organic matter
will be decomposed in the benthic
zone (bottom) → more carbon dioxide
is released
2. Positive feedback cycles in global warming
 increases in absorption of solar radiation
 Albedo: the ability of a surface to reflect
反射率
light. Higher albedo means little light is
absorbed.
 Snow and ice have a high albedo and tend to
reflect so much light that they do not heat up
very much. Soil, rocks and open ocean water
have a lower albedo and tend to warm up more.
2. Positive feedback cycles in global warming
 Global temperature increase → melting
of sea ice increase → albedo decreases
→ more of the sun's energy is absorbed
by exposed rock, soil, and the dark
surface of the oceans → increases global
warming
2. Positive feedback cycles in global warming
 accelerating rates of decomposition
 Temperature increase → enzyme activity
increase → rate decomposition increase
 Peat bogs trap organic matter and act as
泥炭沼泽地
carbon sink.
 When climate change (increase
decomposition), peat bogs become
carbon sources.
2. Positive feedback cycles in global warming
 Permafrost is a type of soil that
exists in very cold climates and is
frozen solid.
 Organic matter is locked up in the
permafrost because the microbes
that carry out the decomposition
cannot survive at such low
temperature.
2. Positive feedback cycles in global warming
 Temperature increase → melting of
permafrost → microbes decompose
the trapped organic matter → carbon
dioxide is released → greenhouse
effect increase
 Some microbes in the permafrost are
methanogenic archaea.
 Melting permafrost can release
methane.
 Methane is also a greenhouse gas.
2. Positive feedback cycles in global warming
 Droughts and forest fires
 Increased global temperatures →
droughts occur more often → increase
the change of fire (combustion) →
release carbon dioxide & reduction in
the number of photosynthesizing
plants
D 4.3.3
北方针叶林
• Change from net carbon accumulation to net loss in boreal forests as
an example of a tipping point
• Include warmer temperatures and decreased winter snowfall leading
to increased incidence of drought and reductions in primary
production in taiga, with forest browning and increases in the
frequency and intensity of forest fires, which result in legacy carbon
combustion.
3. Carbon changes in boreal forest (taiga)
 Boreal (coniferous) forests (also known as
taiga) are distributed across a greater area
than rainforests. They are considered as
carbon sinks.
 Warmer temperature → shorter winters
and less snow → less snowmelt → less
water → drought → lack of water for
photosynthesis → 1. primary production
is reduced, 2. less carbon dioxide is
removed, 3. loss of green pigment (forest
browning) → trees will die
3. Carbon changes in boreal forest (taiga)
 The dead trees dry out and the risk of forest
fires increases
 Combustion can release carbon that has been
locked up for many years in the living trees,
dead needles on the ground, and within the
soil itself; this is known as legacy carbon
combustion
 Forests become carbon sources. The switch
from sink to source because of an imbalance
in the system is considered a tipping point.
D 4.3.4
岸冰
• Melting of landfast ice and sea ice as examples of polar habitat
change
• Include potential loss of breeding grounds of the emperor penguin
(Aptenodytes forsteri) due to early breakout of landfast ice in the
Antarctic and loss of sea ice habitat for walruses in the Arctic.
4. Polar habitat change
 The emperor penguin
 Live along the coasts of Antarctica
 Prefer to breed on sea ice that is
connected to the mainland (landfast ice)
 Temperature increase → landfast
breakout earlier → loss of their
breeding grounds
4. Polar habitat change
海象
 Walruses
 Live in the arctic
 Prefer sea ice shelves as breeding grounds and a place
to rear their young.
 Melting ice → reduced breeding ground and less
space to rear young
 mothers can alternate periods of feeding their young
and hunting for food in the ocean nearby
 The early loss of ice means that nursing mothers need
to care for their young further from the water's edge,
leaving young without protection for longer periods
when the mothers hunt for food
D 4.3.5
• Changes in ocean currents altering the timing and extent of nutrient
upwelling
上涌，上升流
• Warmer surface water can prevent nutrient upwelling to the surface,
decreasing ocean primary production and energy flow through marine
food chains.
5. Ocean current change
传送带
 The oceanic conveyor belt transfer energy around
 Cold, salty water sinks and is replaced by surface water that is warmed in
the tropics.
 As temperature increase → more melting ice → decrease ocean salinity →
slow great ocean current
5. Ocean current change
 Nutrient upwelling: movement of
nutrient-rich water from deeper parts
of the ocean (cold water) towards the
surface
 Warmer surface water can prevent
nutrient upwelling to the surface.
 The ocean primary production
decreases and energy flow through
marine food chains dereaces
D 4.3.6
• Poleward and upslope range shifts of temperate species
• As evidence-based examples, include upslope range shifts for tropical-
zone montane bird species in New Guinea and range contraction and
northward spread in North American tree species.
6. Poleward and upslope range shifts
 Tree species in northern latitudes have been monitored to see if their
ranges are moving. (range migration)
•
A range shift towards the poles is described as a poleward shift
•
A range shift to a higher altitude is an upslope shift
6. Poleward and upslope range shifts
 The northern limit for tree survival is determined by temperature (affect
photosynthesis).
 Various studies of North American tree species have shown range
contraction, i.e. the ranges of these trees have shrunk, and northward
spread for many species
6. Poleward and upslope range shifts
 Montane bird species: birds that live on mountains
 Altitude affects temperature and oxygen availability, so will influence plant
growth and rates of aerobic respiration
 All birds have a certain altitude range they live in.
6. Poleward and upslope range shifts
 If habitat warms up, some birds could go to
higher altitudes to find eh relatively cooler
temperatures.
 Evidence gathered in the mountains of Papua
New Guinea over a 50 year period shows that
many bird species have migrated to higher
altitudes over this time period
 This is not the case for all species; a few have
stayed in the same place or moved downslope
D 4.3.7
• Threats to coral reefs as an example of potential ecosystem collapse
• Increased carbon dioxide concentrations are the cause of ocean
acidification and suppression of calcification in corals. Increases in
water temperature are a cause of coral bleaching. Loss of corals causes
the collapse of reef ecosystems.
7. Ecosystem collapse
 Coral reefs are built from hard calcium
carbonate deposits that are secreted by
coral polyps
珊瑚虫
 These polyps live in a symbiotic
relationship with algae, in which the
algae provide carbon compounds
through photosynthesis, and the coral
polyp provides shelter and protection
within its body
7. Ecosystem collapse
 Coral reefs are some of the most
diverse ecosystems in the world; the
complex structures produced by reefbuilding corals provide habitats for
many species, supporting complex food
chains and providing suitable places to
breed and raise young
•
Around 25 % of the world's ocean fish
species are dependent on coral reefs
for survival
7. Ecosystem collapse
 Death of coral polyps will have a knock-on effect on all other species that
rely on the reef, disrupting food webs, reducing the availability of niches
and therefore reducing the reef biodiversity
•
Many species will die off or migrate to other habitats
•
This leads to ecosystem collapse
7. Ecosystem collapse
 Increased carbon dioxide concentrations in the air lead to increased
dissolved carbon dioxide in the oceans, which lowers the pH of seawater
and makes it acidic.
 It prevents deposition of calcium carbonate.
 It is more difficult for reef- building corals to absorb carbonate ions to make
their skeletons.
7. Ecosystem collapse
 Shells and coral exoskeletons degraded.
 Photosynthetic algae live sheltered and protected in the cells of corals.
 Due to the high water temperature, the algae are expelled. The colour of the
reef becomes white and die (bleaching).
D 4.3.8
造林
• Afforestation, forest regeneration and restoration of peat-forming
wetlands as approaches to carbon sequestration
• NOS: There is active scientific debate over whether plantations of non-
native tree species or rewilding with native species offer the best
approach to carbon sequestration. Peat formation naturally occurs in
waterlogged soils in temperate and boreal zones and also very rapidly
in some tropical ecosystems.
碳吸存
8. Carbon sequestration
 Carbon sequestration：The
process of capturing and storing
carbon dioxide from the
atmosphere
 This can be accomplished by
increasing the removal of
carbon from the atmosphere
into natural carbon sinks
8. Carbon sequestration
 Natural carbon sequestration can be increased by:
 Forest regeneration, or reforestation, involves planting new trees in
deforested areas, while afforestation is the creation of new forests
 Afforestation is the process of planting trees where no forest has
previously existed.
 If trees are allowed to grow to maturity, they can store huge amounts of
carbon in their biomass
 This kind of achievement requires huge government inputs in the form of
benefits to landowners
8. Carbon sequestration
 Peat bog restoration
 Peat bogs form when plant matter
cannot decompose fully due to
waterlogged (anaerobic) and acidic
conditions; the carbon stored in the
partially decomposed plant matter
means that peat bogs are an essential
carbon sink
8. Carbon sequestration
 Human activities include the harvesting of
peat for fuel and the draining of peat bogs
to clear land for development and
agriculture; these activities release carbon
back into the atmosphere by combustion
or decomposition
 Filling in drainage ditches and regulating
peat harvesting can allow peat bogs to
recover and to continue growing in depth;
this restoration of peat bogs increases
their ability to sequester carbon