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Terrestrial Ecology
Part Two
•Biogeochemical Cycles
•Biomes
•Succession
•Natural Selection
Biogeochemical Cycles
 The carbon, phosphorous, nitrogen and sulfur cycles
illustrate the law of conservation of matter
 the 1st law of thermodynamics- energy Is neither
created nor destroyed by it may be converted from
one form to another
Biosphere
Carbon
cycle
Phosphorus
cycle
Nitrogen
cycle
Water
cycle
Oxygen
cycle
Heat in the environment
Heat
Heat
Heat
Fig. 3-7, p. 55
Biogeochemical Cycles
Carbon
 Is an atmospheric cycle but can be found in all three
spheres- air, land and water
 Carbon is required for formation of organic
compounds in living things.
 Carbon is taken out of the air by plants during
photosynthesis and is returned to the air by cellular
respiration.
 Largest reservoir of carbon - sedimentary rocks
(limestone)
 Second largest reservoir of carbon - ocean (dissolved
carbon dioxide), living things in ocean.
The Carbon Cycle:
Part of Nature’s Thermostat
Figure 3-27
Biogeochemical Cycles
Carbon Cycle
1. C in carbon dioxide in atmosphere and in water is moved to C
in glucose by photosynthesis by producers.
2. C in glucose is moved to C in carbon dioxide by cellular
respiration.
3. C in glucose is moved to C in organic molecules by synthesis
reactions in living things.
4. C in organic molecules is moved to C in carbon dioxide by
combustion.
5. C in organic molecules in organisms is moved to C in fossil
fuels over millions of years by pressure, heat, and bacterial
action.
6. C in limestone (CaCO3) is released slowly to C in carbon
dioxide when exposed to oxygen and/or water.
Biogeochemical Cycles
Carbon Cycle- Human
Impacts
We alter the carbon cycle
by adding excess CO2 to
the atmosphere through:
 Burning fossil fuels.
 Clearing vegetation
faster than it is replaced.
Biogeochemical Cycles
Phosphorous Phosphorus is required in the form of phosphate ions for
nucleic acids, ATP, phospholipids in cell membranes, bones,
teeth, shells of animals.
 Does not contain a gaseous phase
 Is a sedimentary cycle - does not include the atmosphere.
 Recycled only if the wastes containing it are deposited in
the ecosystem from which it came
 Limiting factor for plants
Biogeochemical Cycles
 The phosphorus cycle is slow and phosphorus is
usually found in rock formations and ocean sediments.
 Phosphorus is found in fertilizers because most soil is
deficient in it and plants need it.
 Phosphorus is usually insoluble in water and is not
naturally found in most aquatic environments.
Biogeochemical Cycles
 Phosphate on land and in ocean sediment released by
weathering into water and taken up by plants.
 Can be limiting factor for plant growth - is present in artificial
fertilizer.
 Animals get phosphorus by eating plants or other animals.
 Decomposition changes organic molecules with
phosphorus back into phosphate which dissolves in water
which returns the phosphorus to ocean sediment or
deposited as rocks.
The Phosphorous Cycle
Figure 3-31
Biogeochemical Cycles
Phosphorous and Human Impact
 Mining of phosphate for fertilizers and soap causes
disruption to ecosystems.
 Removal of phosphorus from ecosystems by cutting
down of vegetation. Most of phosphorus is taken up as
biomass.
 Excessive phosphate in runoff from fertilizer, discharge
of sewage, farm waste causes growth of algae, etc.
(same problem as nitrogen).
Biogeochemical Cycles
Nitrogen
 Is an atmospheric cycle.
 Plants and animals cannot use free nitrogen gas in the
atmosphere. They must have nitrogen in "fixed" form. Nitrogen
is required for proteins, nucleic acids in living things.
 Nitrogen is often limiting factor in plant growth because
ammonia, ammonium ion, nitrate are water-soluble: can be
leached from soil.
 The main reservoir of nitrogen is in the air
 78% nitrogen gas
 You need phosphorous and nitrogen to build proteins and
nucleic acids (part of DNA)
 Since more organisms are unable to use nitrogen gas (N2),
nitrogen fixing bacteria bind nitrogen with hydrogen to form
ammonia (NH3)
Biogeochemical Cycles
 Stages:
 Nitrogen fixation (atmospheric nitrogen, N2, is
converted to a more usable form by bacteria)
 Assimilation (absorption of nitrates/ammonia, by
plants)
 Ammonification (production of ammonia, NH3, by
bacteria during organism decay)
 Nitrification (production of nitrate from ammonia)
 Denitrification (conversion of nitrate to N2)
Nitrogen Cycle
Fundamental Aspects
Biogeochemical Cycles
Complicated version
Free N2 in atmosphere is "fixed" by nitrogen-fixing bacteria to NH3
(ammonia)
 Nitrogen fixing bacteria live in nodules on the roots of leguminous plants
(soybeans, peas, clover, and alfalfa.)
 Water in the soil reacts with ammonia to form NH4+ (ammonium ion)
 Another species of bacteria can perform nitrification once ammonium
has formed
 Assimilation - absorption of ammonia, ammonium ion, nitrate for use by
plants to make nucleic acids, proteins
 Animals get fixed nitrogen by eating plants or other animals.
 Plants and animals are broken down by still other bacteria that convert
nitrogen-containing organic molecules in organisms to an inorganic form
of nitrogen (ammonia or ammonium ion) = ammonification
 Once this ammonia has formed, still another group of bacteria can
perform denitrification
The Nitrogen Cycle:
Bacteria in Action
Figure 3-29
Biogeochemical Cycles
Nitrogen and Human Impact
 We alter the nitrogen cycle by:
 Adding gases that contribute to acid rain.
 Adding nitrous oxide to the atmosphere through farming
practices which can warm the atmosphere and deplete
ozone.
 Contaminating ground water from nitrate ions in inorganic
fertilizers.
 Releasing nitrogen into the troposphere through
deforestation.
 Planting many legume crops
 Accelerates the normal rate of nitrogen fixation
 Human activities
such as production
of fertilizers now fix
more nitrogen than
all natural sources
combined.
Figure 3-30
Biogeochemical Cycles
Sulfur Cycle
 Is an atmospheric cycle.
 H2S (hydrogen sulfide) and SO2 (sulfur dioxide)
released into atmosphere from natural (volcanoes)
and non-natural sources.
Biogeochemical Cycles
Sulfur and the Human Impact
 We add sulfur dioxide to the atmosphere by:
 Burning coal and oil
 Refining sulfur containing petroleum.
 Convert sulfur-containing metallic ores into free metals
such as copper, lead, and zinc releasing sulfur dioxide
into the environment.
Biomes
Biomes
 Temperature and precipitation define a biome
 As you move from Arctic to equator, generally speaking,
there is an increase in mean annual temp and mean
annual precipitation
 Biomes tend to converge around latitude lines on the
globe.
 Separated by physical barriers
 Ocean, mountains, etc
Biomes
Terrestrial Biomes Desert
 Temperate Grassland
 Woodland
 Chaparral
 Tundra
 Tropical Forests
 Temperate rainforests
 Temperate deciduous forests
 Coniferous Forests
 Taigas/Boreal Forest
 You need to study the difference between these
biomes
BIOMES
Human Impacts on Terrestrial Biomes
 Human activities have damaged or disturbed more than
half of the world’s terrestrial ecosystems.
 Humans have had a number of specific harmful effects on
the world’s deserts, grasslands, forests, and mountains.
 Remember HIPPO? It applies here as well
Biomes
Aquatic Biomes Lakes and Ponds
 Streams and Rivers
 Wetlands
 Estuaries
 Coastal Oceans
 Open Oceans
Succession
Succession
 Transition of one biotic community to the next
 New environmental conditions allow one group of
species in a community to replace other groups.
 Ecological succession: the gradual change in species
composition of a given area
 Primary succession: the gradual establishment of biotic
communities in lifeless areas where there is no soil or
sediment.
 Secondary succession: series of communities develop in
places containing soil or sediment.
Succession
Primary Succession:
Starting from Scratch
Primary succession begins with
an essentially lifeless are where
there is no soil in a terrestrial
ecosystem
Examples:
- Lichen growing on a bare rock
- Glaciers recede and expose
uninhabited soil
- Abandoned parking lot
- An area after a volcanic
eruption where lava covered
and hardened over the soil
Figure 7-11
Succession
 Pioneer species-
 First organisms to live in a
new community
 Usually brought in by wind
or animals
 Examples Moss, weeds, lichen,
opportunistic species
Succession
Primary Succession
 Mosses invade an area
and provide a place for
soil to accumulate.
 Larger plants germinate
in the new soil layer
resulting in additional
soil formation.
 Eventually shrubs and
trees will invade the
area.
Succession
Secondary Succession:
Starting Over with
Some Help
Secondary succession
begins in an area
where the natural
community has
been disturbed.
Figure 7-12
Succession
 Secondary
 Usually takes place after a
land clearance
 Fire, landslide, forest clearing
 Soil is already there
 More rapid than primary
One Year Later…
Thirteen Years Later…
Succession
 Each successive (new) community is more favorable for new
species
 Changes in stages until a climax community is established
 The area is dominated by a few, long lived plant species
 Nothing can “succeed” the plants in this community unless
some sort of natural disaster/act of mother nature occurs
Succession
 Aquatic Succession
 When a body of water is taken over by vegetation
 Water becomes shallow, less water volume and more fertile
Aquatic Succession
This used to be a lake!