Transcript Ecology3e Ch25 Lecture KEY

25
Global Ecology
Chapter 25 Global Ecology
CONCEPT 25.1 Elements move among
geologic, atmospheric, oceanic, and
biological pools at a global scale.
CONCEPT 25.2 Earth is warming due to
anthropogenic emissions of greenhouse
gases.
Chapter 25 Global Ecology
CONCEPT 25.3 Anthropogenic emissions
of sulfur and nitrogen cause acid
deposition, alter soil chemistry, and affect
the health of ecosystems.
CONCEPT 25.4 Losses of ozone in the
stratosphere and increases in ozone in the
troposphere each pose risks to organisms.
Introduction
Movements of biologically important
elements are linked at a global scale that
transcends ecological boundaries.
Humans are increasingly changing the
physical and chemical environment on a
global scale.
Introduction
Atmospheric emissions of pollutants, dust,
and greenhouse gases have caused
widespread environmental problems.
A major focus of global ecology is the
study of the environmental effects of
human activities.
CONCEPT 25.1
Elements move among geologic,
atmospheric, oceanic, and biological pools
at a global scale.
Concept 25.1
Global Biogeochemical Cycles
Global cycling of carbon (C), nitrogen (N),
phosphorus (P), and sulfur (S) are
emphasized because of their biological
importance and their roles in human
alteration of the global environment.
Concept 25.1
Global Biogeochemical Cycles
Pool, or reservoir: Amount of an element
in a component of the biosphere.
Flux: Rate of movement of an element
between pools.
Examples: Terrestrial plants are a pool of
carbon; photosynthesis represents a
flux.
Concept 25.1
Global Biogeochemical Cycles
The Carbon Cycle:
C is critical for energy transfer and the
construction of biomass.
C is dynamic, moving between different
pools over time scales of weeks to
decades.
Concept 25.1
Global Biogeochemical Cycles
Changes in the global C cycle are
influencing Earth’s climate.
C in the atmosphere occurs primarily as
carbon dioxide (CO2) and methane
(CH4).
Both are greenhouse gases that affect
the global climate.
Figure 25.3 The Global Carbon Cycle
Concept 25.1
Global Biogeochemical Cycles
Anthropogenic release of C to the
atmosphere from the terrestrial pool
results from land use change, mostly
deforestation (20%); and from burning
fossil fuels (80%).
Before the mid-nineteenth century,
deforestation was the main
anthropogenic flux.
Concept 25.1
Global Biogeochemical Cycles
Removing the forest canopy warms the
soil, increasing rates of decomposition
and respiration.
Burning trees releases CO2, and small
amounts of CO and CH4.
In the 20th century, major deforestation
shifted from the mid-latitudes to the
tropics.
Concept 25.1
Global Biogeochemical Cycles
Anthropogenic emissions of CO2 more
than doubled from 1970 to 2011.
About half is taken up by the oceans and
terrestrial biota.
But this proportion will decrease because
terrestrial and ocean uptake will not
keep pace with the rate of atmospheric
increase.
Concept 25.1
Global Biogeochemical Cycles
Anthropogenic emissions of CH4 have
also increased.
Atmospheric CH4 levels are much lower
than CO2, but CH4 is a more effective
greenhouse gas.
Concept 25.1
Global Biogeochemical Cycles
Anthropogenic sources of CH4 include:
• Burning fossil fuels
• Agricultural development (primarily
rice grown in flooded fields)
• Burning of forests and crops
• Livestock production
Concept 25.1
Global Biogeochemical Cycles
Higher concentrations of CO2 may
stimulate photosynthesis.
But experiments have shown that
increased photosynthetic rates may be
short lived, and plants will acclimate to
higher concentrations.
For forest trees, increased CO2 uptake
may be sustained longer.
Concept 25.1
Global Biogeochemical Cycles
Ocean acidity has increased 30% over
the last century. Further increase is
predicted by models.
Many marine organisms form shells of
carbonate.
Increasing acidity will dissolve existing
shells and lower carbonate
concentrations will decrease the ability
to synthesize new shells.
Concept 25.1
Global Biogeochemical Cycles
On Australia’s Great Barrier Reef,
calcium carbonate formation declined by
14% from 1990 to 2009.
Anthropogenic CO2 emissions therefore
have potential to tremendously alter the
diversity and function of marine
ecosystems.
Figure 25.5 Rates of Calcification of Corals on Australia’s Great Barrier Reef, 1900–2005
Concept 25.1
Global Biogeochemical Cycles
Since the mid-19th century, CO2
concentrations have increased at a rate
faster than at any other time in the past
400,000 years.
Even if CO2 emissions are reduced
dramatically, CO2 levels will remain high
due to a time lag in ocean uptake
(decades to centuries).
Concept 25.1
Global Biogeochemical Cycles
The Nitrogen Cycle:
N is a constituent of enzymes and
proteins and often limits primary
productivity.
N and C cycles are tightly coupled
through the processes of photosynthesis
and decomposition.
Concept 25.1
Global Biogeochemical Cycles
The largest N pool is atmospheric N2,
which is not available to most
organisms.
N-fixing bacteria are able to convert it to a
useable form.
Fixed N compounds are called reactive—
they can participate in chemical
reactions.
Concept 25.1
Global Biogeochemical Cycles
Humans have altered the N cycle even
more than the C cycle.
Rate of N2 fixation by humans now
exceeds natural biological rates.
Emissions of N from industrial and
agricultural activities cause widespread
environmental changes, including acid
precipitation.
Figure 25.8 Changes in Anthropogenic Fluxes in the Global Nitrogen Cycle
Concept 25.1
Global Biogeochemical Cycles
Fertilizers are made using the Haber–
Bosch process.
Growing N-fixing crops such as alfalfa,
soybeans, and peas has increased
biological N2 fixation.
Flooding of agricultural fields for rice has
increased N2 fixation by cyanobacteria.
Concept 25.1
Global Biogeochemical Cycles
Many other forms of reactive N are
emitted to the atmosphere, mostly from
fossil fuel combustion.
These compounds can undergo chemical
reactions in the atmosphere and are
potentially available for biological uptake.
They are returned to ecosystems by
atmospheric deposition.
Concept 25.1
Global Biogeochemical Cycles
The Phosphorus Cycle:
P can limit primary productivity in aquatic
ecosystems and some terrestrial
ecosystems.
P availability can control the rate of Nfixation, which has a high metabolic
demand for P.
Concept 25.1
Global Biogeochemical Cycles
The C, N, and P cycles are linked through
photosynthesis and NPP,
decomposition, and N2 fixation.
P has no atmospheric pool, except as
dust.
The largest pools are in soils and marine
sediments.
Figure 25.9 The Global Phosphorus Cycle
Concept 25.1
Global Biogeochemical Cycles
P in aquatic systems is lost to the
sediments. This is cycled again with
tectonic uplift and weathering of rocks.
Human influences on the P cycle include
agricultural fertilizers, sewage and
industrial wastes, and increased
terrestrial erosion.
Concept 25.1
Global Biogeochemical Cycles
P fertilizers are made from marine
sedimentary rock.
Mining releases four times more P than
natural rock weathering.
Flux of anthropogenic P from terrestrial to
aquatic ecosystems can have negative
impacts such as eutrophication.
Concept 25.1
Global Biogeochemical Cycles
The Sulfur Cycle:
S is a constituent of some amino acids,
DNA, and RNA, but is probably never
limiting to growth.
Major pools of S are in rocks, sediments,
and oceans as dissolved sulfate (SO42–).
Figure 25.10 The Global Sulfur Cycle
Concept 25.1
Global Biogeochemical Cycles
In the atmosphere, S compounds are
transformed to SO42– and H2SO4
(sulfuric acid), which are removed
quickly by precipitation.
Anthropogenic emissions have
quadrupled since the Industrial
Revolution. Most comes from burning
sulfur-containing coal and oil and from
smelting.
CONCEPT 25.2
Earth is warming due to anthropogenic
emissions of greenhouse gases.
Concept 25.2
Global Climate Change
Climate change, especially change in
frequency of extreme events (droughts,
storms, etc.) will have profound effects on
ecosystems.
Extreme events are often critical in
determining species’ geographic ranges.
Concept 25.2
Global Climate Change
Weather: Current state of the atmosphere
at any given time.
Climate: Long term description of
weather, including average conditions
and the full range of variation.
Climate variation occurs at multiple time
scales—from daily and seasonal to
decadal.
Concept 25.2
Global Climate Change
Climate change refers to directional
change in climate over a period of at
least three decades.
Earth is currently experiencing significant
climate change (IPCC 2013).
Average global surface temperature
increased 0.8°C between 1880 and
2012.
Figure 25.11 Changes in Global Temperature and Precipitation (Part 1)
Concept 25.2
Global Climate Change
Associated with this warming, there has
been:
• Widespread retreat of mountain
glaciers
• Thinning of the polar ice caps
• Melting permafrost
• A 19-cm rise in sea level since 1900
Concept 25.2
Global Climate Change
The warming trend has not been
consistent around the globe.
Some regions have seen greater
warming, especially mid- to high
latitudes in the Northern Hemisphere.
Figure 25.11 Changes in Global Temperature and Precipitation (Part 2)
Concept 25.2
Global Climate Change
Precipitation in the high latitudes of the
Northern Hemisphere has increased, but
weather has been drier in the subtropics
and tropics.
There is also a trend of increasing
frequency of extreme weather events
such as hurricanes and heat waves.
Concept 25.2
Global Climate Change
Greenhouse effect: Warming of Earth by
atmospheric absorption and reradiation
of infrared radiation emitted by Earth’s
surface.
It is due to greenhouse gases in the
atmosphere, primarily water vapor, CO2,
CH4, and N2O.
Figure 25.12 Atmospheric Concentrations of Greenhouse Gases
Concept 25.2
Global Climate Change
The Intergovernmental Panel on Climate
Change (IPCC) was established in 1988.
It includes experts in atmospheric and
climate science from around the world.
They use modeling and analysis of data
from the scientific literature to evaluate
underlying causes of observed climate
change and scenarios for the future.
Concept 25.2
Global Climate Change
The IPCC releases assessment reports to
promote understanding of climate
change among scientists, policymakers,
and the general public.
In recognition of their efforts to spread
“knowledge about man-made climate
change,” the IPCC was awarded the
Nobel Peace Prize in 2007.
Concept 25.2
Global Climate Change
In the third report (2001), the IPCC
concluded that the majority of the
observed global warming is attributable
to human activities.
While this conclusion is debated in the
political arena, it is backed by the
majority of the world’s leading
atmospheric scientists.
Figure 25.13 Contributors to Global Temperature Change
Concept 25.2
Global Climate Change
The certainty of anthropogenic cause of
climate change has increased with each
new IPCC report.
The 2013 report states “It is extremely
likely (95%–100% probability) that
human influence has been the dominant
cause of the observed warming since
the mid-20th century.”
Concept 25.2
Global Climate Change
Paul Crutzen and Eugene Stoermer have
suggested that we have entered a new
geological period, called the
Anthropocene epoch, to indicate the
extensive impact of humans on our
environment.
Concept 25.2
Global Climate Change
IPCC models predict an additional
temperature increase of 1.1 to 4.8°C in
the 21st century.
The range is associated with uncertainty
of future greenhouse gas emissions and
the behavior of Earth’s climate system.
Concept 25.2
Global Climate Change
What does a 1.1° to 4.8°C change in
temperature mean for biological
communities?
It can be compared with elevational
climate change on a mountain.
The median value (2.9°C) would
correspond to a 500 m shift in elevation.
Concept 25.2
Global Climate Change
Because climate change will be rapid,
most plants and animals will not be able
to respond with evolutionary change.
Dispersal may be the only way to avoid
extinction.
Dispersal barriers and habitat
fragmentation will be important
constraints.
Concept 25.2
Global Climate Change
Plant dispersal rates are generally much
slower than the predicted rate of climate
change.
Ruderal (weedy) herbaceous plants and
plants with animal-dispersed seeds can
disperse and establish quickly.
Shrubs and trees have much slower
dispersal rates; there may be time lags
in their response.
Concept 25.2
Global Climate Change
For animals, their habitat and food
requirements are associated with
specific vegetation types.
Barriers to dispersal can prevent
migration of many kinds of organisms—
dams, habitat fragmentation, etc.
Concept 25.2
Global Climate Change
Organisms have already begun to
respond to climate change (e.g., earlier
migration of birds, local extinction of
amphibian and reptile populations,
earlier leaf-out of vegetation).
Geographic ranges of many species have
shifted.
Concept 25.2
Global Climate Change
Ranges of plant species in the European
Alps were compared with historical
records (Grabherr et al. 1994).
A consistent trend of upward movement
of species from lower elevations onto
the summits was reported.
Figure 25.15 Plants Are Moving Up the Alps
Concept 25.2
Global Climate Change
Extinction of lizard populations in Mexico
has been linked to warmer spring
temperatures, which limits foraging time
during the breeding season (Sinervo et
al. 2010).
Using models of lizard physiology and
projections for climate warming, they
predict 39% of lizard populations will go
extinct by 2050.
Concept 25.2
Global Climate Change
Migratory animals may be affected:
• Fish and whales may have to make
longer journeys to find prey.
• Birds arrive earlier in spring, but
plants and invertebrates they depend
on for food may not be available at
the same time.
Concept 25.2
Global Climate Change
Changes in community composition and
local extinctions may be indicators of
climate change.
Example: Warmer water has affected
coral reef community structure.
CONCEPT 25.3
Anthropogenic emissions of sulfur and
nitrogen cause acid deposition, alter soil
chemistry, and affect the health of
ecosystems.
Concept 25.3
Acid and Nitrogen Deposition
Since the Industrial Revolution, air
pollution has been associated with
urban industrial centers, power plants,
and oil and gas refineries.
Increasing emissions from cars, taller
smokestacks, and widespread industrial
development have increased the spatial
extent of air pollution.
Concept 25.3
Acid and Nitrogen Deposition
Emissions of N and S have resulted in
two related issues:
• Acid precipitation
• N deposition
Sites affected by these problems now
include national parks and wilderness
areas.
Figure 25.17 Air Quality Monitoring in Grand Canyon National Park
Concept 25.3
Acid and Nitrogen Deposition
Awareness of the widespread effects of
acid precipitation, even in pristine areas,
increased during the 1960s.
Damage to forests and aquatic
ecosystems became well-known.
Concept 25.3
Acid and Nitrogen Deposition
Large-scale mortality of trees in European
forests during the 1970s and 1980s was
associated with acid precipitation, Ca
and Mg deficiencies, and other stresses.
Figure 25.18 Air Pollution Has Damaged European Forests
Figure 25.19 Decreases in Acid Precipitation
Concept 25.3
Acid and Nitrogen Deposition
Increased N supplies might be expected
to increase plant growth and production.
Primary production has increased in
some ecosystems.
It may be partly responsible for a greater
uptake of atmospheric CO2 by terrestrial
ecosystems.
Concept 25.3
Acid and Nitrogen Deposition
But N deposition is also associated with
environmental degradation, loss of
diversity, and acidification.
Nitrogen saturation—N deposition may
exceed the capacity of plants and
microbes to take it up.
Figure 25.21 Effects of Nitrogen Saturation
Concept 25.3
Acid and Nitrogen Deposition
• N export to nearshore marine
ecosystems contributes to
eutrophication and oxygen depletion.
 Anoxic conditions over large areas
are called “dead zones.”
Concept 25.3
Acid and Nitrogen Deposition
• In nutrient-poor environments, many
plants have adaptations that lower
their nutrient requirements, which
lowers their capacity to take up
excess N.
 Faster-growing species may then
outcompete them, resulting in loss
of biodiversity and change in
community composition.
Concept 25.3
Acid and Nitrogen Deposition
In Holland, species-rich heath
communities, adapted to low-nutrient
conditions, have been replaced by
species-poor grassland communities as
a result of very high rates of N
deposition.
Concept 25.3
Acid and Nitrogen Deposition
A survey of grasslands in Great Britain
looked at a range of N deposition rates
(Stevens et al. 2004).
Of 20 factors that may have influenced
species richness, N deposition rate
explained the most variation.
Higher N inputs were associated with
lower species richness.
Figure 25.22 Nitrogen Deposition Lowers Species Diversity
Concept 25.3
Acid and Nitrogen Deposition
Many experimental studies have also
shown that adding N to experimental
plots decreases species richness, often
resulting in loss of rare species.
High N deposition rates also facilitate the
spread of some invasive plant species.
CONCEPT 25.4
Losses of ozone in the stratosphere and
increases in ozone in the troposphere each
pose risks to organisms.
Concept 25.4
Atmospheric Ozone
Statospheric ozone (O3) protects Earth’s
surface from high-energy ultraviolet-B
(UVB) radiation.
UVB radiation causes damage to DNA
and photosynthetic pigments,
impairment of immune responses, and
cancerous skin tumors in animals.
Concept 25.4
Atmospheric Ozone
Stratospheric ozone concentrations
decrease in spring in polar regions.
In 1980, British scientists measured an
unusually large decrease in springtime
ozone over Antarctica.
This phenomenon is known as the
ozone hole, and it has increased in
intensity and spatial extent.
Figure 25.23 The Antarctic Ozone Hole (Part 1)
Figure 25.23 The Antarctic Ozone Hole (Part 2)
Concept 25.4
Atmospheric Ozone
An ozone hole is not really a hole, but an
area with low ozone concentrations.
In the Arctic, the decreases have not
been as great (the Arctic ozone dent).
Concept 25.4
Atmospheric Ozone
Molina and Rowland (1974) predicted the
decrease in stratospheric ozone due to
manmade compounds called
chlorofluorocarbons (CFCs).
CFCs were developed in the 1930s as
refrigerants and propellants in spray
cans of paint, deodorants, hair spray,
etc.
Concept 25.4
Atmospheric Ozone
In the stratosphere, CFCs react with other
compounds to produce reactive chlorine
atoms that destroy ozone.
A single free chlorine atom can destroy
105 ozone molecules.
Amount of UVB radiation at Earth’s
surface increased as stratospheric
ozone concentration decreased.
Concept 25.4
Atmospheric Ozone
Increased UVB radiation is correlated
with higher incidence of skin cancer in
humans.
UVB radiation influenced evolution of skin
pigmentation in humans. The pigment
melanin was selected for in populations
at low latitudes where ozone levels are
naturally lowest.
Concept 25.4
Atmospheric Ozone
Several international conferences on
ozone destruction took place in the
1980s.
The Montreal Protocol is an international
agreement calling for reduction and
eventual ban on CFCs and other ozonedegrading chemicals.