Ecology
CO
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
2
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
Processes in Carbon Cycling
‣ Carbon cycles between the
living (biotic) and non-living
(abiotic) environments.
Burning fossil fuels
Gaseous carbon is fixed in the
process of photosynthesis and
returned to the atmosphere in
respiration.
Carbon may remain locked up
in biotic or abiotic systems for
long periods of time, e.g. in
the wood of trees or in fossil
fuels such as coal or oil.
Humans have disturbed the
balance of the carbon cycle
through activities such as
combustion and deforestation.
Petroleum
The Carbon Cycle
Nitrogen in the Environment
‣ Nitrogen cycles between the biotic
and abiotic environments. Bacteria
play an important role in this transfer.
Nitrogen-fixing bacteria are able to fix
atmospheric nitrogen.
Nitrifying bacteria convert ammonia
to nitrite, and nitrite to nitrate.
Denitrifying bacteria return fixed
nitrogen to the atmosphere.
• Atmospheric fixation also occurs as a
result of lightning discharges.
‣ Humans intervene in the nitrogen
cycle by producing and applying
nitrogen fertilizers.
Nitrogen Transformations
‣ The ability of some bacterial species to fix
atmospheric nitrogen or convert it between
states is important to agriculture.
Nitrogen-fixing species include Rhizobium,
which lives in a root symbiosis with leguminous
plants. Legumes, such as clover, beans, and
peas, are commonly planted as part of crop
rotation to restore soil nitrogen.
Nitrifying bacteria include Nitrosomonas and
Nitrobacter. These bacteria convert ammonia to
forms of nitrogen available to plants.
NH3
NO2Nitrosomonas
NO3Nitrobacter
Root nodules
in Acacia
Nodule
close-up
Nitrogen Cycle
The Phosphorus Cycle
Guano
deposits
Sulfur Cycling
• Sulfur is an essential component of proteins
and is important in determining the acidity
of precipitation, surface water, and soil.
• Sulfur circulates through the biosphere as:
Sulfur in petrol
hydrogen sulfide (H2S)
sulfur dioxide (SO2)
sulfate (SO42-)
elemental sulfur (S)
Molecular bridges in proteins
• Human activity releases large quantities of
sulfur through:
combustion of sulfur-containing coal and oil,
refining petroleum,
smelting, and other industrial processes
Elemental sulfur
The Sulfur Cycle
SO2 from
combustible
fossil fuels
Sulfates in the atmosphere (SO42-)
Acid
precipitation
SO2 and sulfates
from volcanoes,
hot springs and
biogenic activity
Sulfur in living organisms
Decomposition and
other processing
Mining
Uplifting in
groundwater
and and
weathering
Sulfates in
soil(SO42-)
Reduced sulfur
(H2S)
Microorganisms
Inorganic
sulfur
Sulfur in fossil
fuels
Iron sulfides in deep
soil and sediments
Sulfates in
water (SO42-)
Uptake by
plants
Sedimentation of
sulfides and sulfates
Organic deposition
Transport overland: net movement of water vapor by wind
The Water Cycle
Condensationconversion of
gaseous water vapor into liquid
water
Precipitation
(rain, sleet, hail, snow, fog)
Rain clouds
Evaporation
from inland
lakes and rivers
Precipitatio
n to land
Transpiration
Evaporatio
n from the
land
Precipitation
Precipitation
over the
ocean
Surface
runoff
(rapid)
Transpiration
from plants
Evaporation
Evaporation
from the
ocean
Rivers
Water locked up
in snow and ice
Ocean storage
97% of total water
Lakes
Infiltration: movement
of water into soil
Percolation: downward
flow of water
Aquifers:
groundwater storage
areas
Groundwater movement (slow)