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Chapter 9
Focus on the Biota: Metabolism,
Ecosystems and Biodiversity
Major environmental issues associated with
Global Change on short-time scales
Global Warming
Stratospheric Ozone Depletion
Deforestation and Loss of Biodiversity
Components of the Earth system
through which elements (such as C)
recycle. The biosphere plays an
important role in many interactions
and in the recycling of elements.
Fundamental characteristics of life that allow it to interact with
the physical processes that occur on the planet in such a way
that Earth is a habitable planet.
1. Life spreads exponentially
2. Life needs energy
3. Life “pollutes”
4. Life is versatile
2 ways for classifying life:
1. in a ‘systems-way’ according to processes, related to the use
of energy and other interactions with the ecosystem
2. Taxonomy, with regards to the physiological and
evolutionary relationships between organisms
Recall that CO2 and CH4 are greenhouse gases - methanogenous are
important as either (a) autotrophic or (b) heterotrophic
(a) CO2 + 4H2
CH4 + 2H2O
(b) CO3COOH
CH4 + CO2
The net result of the activity of methanogenous and oxygenic
photosynthesizers is to release O2 and CH4 to the atmosphere:
Oxygenic photosynthesis:
Fermentation:
2CO2 + 2 H2O
“CH2O” + 2O2
2 “CH2O”
CH3COOH
Heterotrophic methanogenesis: CH3COOH
CH4 + CO2
_________________________________________________________________
NET:
CO2 + 2 H2O
CH4 + O2
SIGNATURE OF LIFE
Lovelock points out that our atmosphere is far from chemical
equilibrium, but obviously dynamically stable.
Chemical Equilibrium: All reactions have an equilibrium constant
associated with them, which indicates the ratio of products to
reactants (depending on temperature and other conditions).
For example:
H2CO3
atm
mixed
layer
 H+ + HCO3- carbonic acid – bicarbonate K=4.4E-7
(CO2)g THE INORGANIC CARBON CYCLE:
interaction with the biological pump
(CO2)aq
H2CO3
HCO3-
CO32-
SIGNATURE OF LIFE
Lovelock points out that our atmosphere is far from chemical
equilibrium, but obviously dynamically stable.
Without biological processes (i.e. life), the atmosphere would be in
chemical equilibrium (such as exists on other planets). The fact that
the atmosphere of our planet is in a state of chemical disequilibrium
is a signature of life! In fact, one way to try to identify the presence
of life on other planets is to see if the atmospheric constituents are in
equilibrium or not.
Yet, the chemical composition of the atmosphere has been very
stable over long periods of time because of the systems dynamics,
which includes the biogeochemical cycles in which life plays an
important role.
Structure of the Biosphere
• species – all closely related
organisms that can potentially
interbreed.
• population – all the members of
a single species that live in a
region
• community – 2 or more groups
of interacting species
• biome – region with a
characteristic plant community
(desert, boreal forest)
• ecosystem – communities with
the physical environment that
supports them
Possible feedbacks between the boreal forest and climate - from
experiments conducted with a General Circulation Model – change
all forest north of 45N to bare ground and compare to actual forest –
equivalent to moving forest line south
Implied by Model Results
positive coupling
Model Results
positive feedback
negative coupling
1.
increase in wintertime albedo – trees prevent snow from covering
homogeneously the area – less trees more snow on bare ground - albedo
increased
2.
decrease in Tair – in April about 12 deg C drop in T
3.
colder T in winter leads to increase in sea-ice cover which in turn leads to
higher albedo of the area
4.
this further higher albedo leads to a decreased Tair
5.
Implied by this results: more sea-ice keeps SSTs lower decreasing the ocean’s
thermal content which keeps high-latitude Tair unusually low and so the
forest is prevented from re-growing
We might say that the forest ‘keeps’ the climate that it needs to
grow healthily: it prevents winter T from being dangerously low for
its own survival!
The figure presents a systems diagram of the feedbacks involving boreal forest
cover, albedo, temperatures, sea ice, and the oceans. The diagram helps us see
that it is possible for the northern boreal forest to have a significant impact on the
larger-scale climate.
Now use information you have about the possible impacts of anthropogenically
induced greenhouse climate change and this diagram to discuss the implications
in terms of climate and forest cover (Critical-Thinking Problem 1).
What do you already know? That anthropogenically induced greenhouse change
is a warming trend in the earth’s climate, and in particular that this means
increased winter temperatures.
So the question can be re-stated now: according to the system diagram of this
figure, what are the implications of increased winter temperatures for the climate
and forest of high latitudes? Warmer winter temperatures would lead to a
decrease in sea ice, which would lead to a decrease in albedo and an increase in
sea-surface temperatures (SSTs). The increased SSTs lead to increased highlatitude summer temperatures, which would lead to increased boreal forest cover.
The increase in boreal forest cover would lead to a decrease in albedo. The
decrease in albedo resulting from both increased boreal forest cover and
decreased sea ice would lead to higher winter temperatures. In sum: this would
be a positive feedback cycle that would accentuate the climatic changes caused
by global warming.
Ecosystems overlap, gradually merge, transitional boundaries:
ecotones
Decomposers
Feed on dead
organic matter
from all levels
‘who-eats-whom’ diagram – food chains are interconnected as food webs
Trophic levels – series of feeding levels
The amount of biomass decreases by 1-2 orders of magnitude (90-99%)
at every level. Why?
Interactions between species can be cooperative, mutually
supportive – bees and trees: one gets food the other reproduces.
An extreme form of this support is symbiosis – coral and plantlike dinoflagellates.
Another extreme is complete competitive coexistence, but less
often than one might think.
Disruptions of ecosystems’ dynamics is generally followed by a
predictable pattern of rebuilding – succession. Unpredictability
(Stochastic Processes) in these patterns leads to diversity.
Biodiversity
Measures of Biodiversity
Diversity of Interactions
Diversity = Stability?
homogeneous
heterogeneous
Measures of Biodiversity
Simpson’s diversity index measures the likehood
(probability) that two individuals chosen at random from
the same community will be of different species :
Sd = Simpson’s diversity = 1 - [(PA)2 + (PB)2 + (PC)2 + ...]
where PA is the proportion of species A (B, C, etc.) in the
community = probability that an individual chosen
randomly will be of species A (B, C, etc.). In this
example:
Sd = 1 - (0.99)2 + (0.01)2 = 0.02 Community I
Sd = 1 - (0.5)2 + (0.5)2 = 0.50
Community II
Assignment 1-To discuss next class
Take “A Closer Look” at Physiology vs Ecological Optimal
Growth – Box, page 178 – Read it once to understand the
basic concepts. Then
1. Explain the graphs of figure 9.1
2. Describe briefly, but clearly, the two paradoxes referred to in
the text of the box