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2.5 Ecosystem level
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An ecosystem consists of a community (group of living organisms) and
the physical environment (Starr & Taggart 1989) and chemical
environment (Mader 1998) in which they live.
The living organisms are the biotic components of the ecosystem while the
physical and chemical environment forms the abiotic components.
In an ecosystem, living things are classified b the ways in which they
source out their food; autotrophs and heterotrophs each occupying its
own trophic level.
In an ecosystem, organisms interact with each other and the environment.
According to Starr and Taggart (1989) this interaction is characterized by 1)
the flow of energy, and 2) a cycling of materials both of which have a
consequences for community structure and the environment.
2.5.1 Basic components of an ecosystem
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Components of an ecosystem can be subdivided into the biotic (includes all living
organisms) and abiotic components (includes water, carbon dioxide, various
minerals, oxygen and continuous supply of energy from the sun).
2.5.1.1 Biotic components of an ecosystem
Autotrophs produce their own food or organic nutrients for themselves and others;
therefore they are regarded as primary producers. These autotrophs can further be
broken down into chemoautotrophs (includes bacteria that obtain energy by oxidising
inorganic compounds such as nitrite, ammonia and sulphides to synthesize
carbohydrates) and photoautotrophs (photosynthesizers which uses energy from the
sun, water and atmospheric carbon dioxide to produce carbohydrates, proteins and
nucleic acids and so forth).
Heterotrophs are consumers of the preformed organic nutrients. They are classified
into herbivores (animals that graze directly of plants), carnivores (feed on other
animals), omnivores (animals that feed on both plants & animals) and detrivores
(organisms that feeds on detritus – decomposing particles of organic matter).
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Note: within detrivores are decomposers which break down dead organic matter
into simple inorganic substances that are released back into the ecosystem and
can be taken up again by producers.
2.5.1.2 Abiotic components of an ecosystem
• Autotrophs synthesize organic nutrients from available inorganic nutrients (carbon
oxide, water and solar energy) through photosynthesis.
• Energy from the sun is converted into a useful form by autotrophs for
heterotrophs
• This phenomenon resonates well with the laws of thermodynamics (first law) in
that energy cannot be created or destroyed (support idea that ecosystem is not
self-sustaining i.e. relies in continuous source of energy).
• Second law states that with every transformation of energy from one level to
another, some energy is degraded or lost between such levels as heat.
• Energy produced by plants (gross productivity) is used to satisfy cellular their
needs and is thus lost as heat. The remaining energy (net productivity) becomes
available for heterotrophs to use and in most cases it is reduced to about 55%.
• Secondary and tertiary consumer will use this energy for cellular respiration (which
is subsequently lost as heat) and increased body weight. The latter use of energy is
called secondary productivity.
2.5.2 Structure of ecosystems
Ecosystem structure continues…
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A pyramid of numbers tells how many organisms there are in each trophic level.
The number of primary producers ought to be high in order to support organisms
at the subsequent trophic level because not all of the food eaten is useful. Energy
efficiency drops as the trophic level ascend. The number of organism occupying
the highest trophic level ought to be few so they can benefit from the availble
energy.
A pyramid of biomass shows relationship between biomass and trophic level by
quantifying the amount of biomass present at each trophic level. Typical units for a
biomass could be grams per m2, or calories per m2. Biomass pyramids provide a
single snapshot in time of an ecological community.
The pyramid of energy also called the pyramid of productivity is one such useful
pyramid in ecology. It shows production or turnover of biomass at each trophic
level. Instead of showing a single snapshot in time, productivity pyramid show the
flow of energy through the food chain. 10% rule in ecological pyramids of energy
and biomass.
2.5.3 Biogeochemical Cycles
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Biogeochemical cycles or nutrient cycles are pathways by which chemical elements
or molecule moves through both biotic (biosphere) and abiotic (lithosphere,
atmosphere and hydrosphere) components of Earth. In effect, the elements are
recycled, although in some cycles there may be places (called reservoirs) where
the elements are accumulated or held for a long period of time. Elements,
chemical compounds, and other forms of matter are passed from one organism to
another and from one part of the biosphere to another through the
biogeochemical cycles.
There are many biogeochemical cycles but he most well-known and important
cycles includes the carbon cycle, the nitrogen cycle, the oxygen cycle, the
phosphorus cycle, and the water cycle.
2.5.3.1 Biogeochemical Cycles
Water
Nitrogen
Carbon Dioxide
Phosphorus
Sulfur
What are biogeochemical cycles?
• Earth system has four parts
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Atmosphere
Hydrosphere
Lithosphere
Biosphere
• Biogeochemical cycles: The chemical
interactions (cycles) that exist between the
atmosphere, hydrosphere, lithosphere, and
biosphere.
• Abiotic (physio-chemical) and biotic
processes drive these cycles
• Focus on carbon and water cycles (but could
include all necessary elements for life). N cycle weakly touched on!
What is common amongst them?
• Each compound (water, carbon, nitrogen)
typically exists in all four parts of the Earth
System
• There are
– ‘Pools’
– Fluxes in and out of pools
– Chemical or biochemical transformations
• Transformations
– are important
– can lead to positive & negative consequences
Transformations
Examples of Transformations
1. Carbon cycle: Organic compounds to CO2
(processes: respiration, decomposition, or fire)
2. Carbon cycle: CO2 to organic compounds (process:
photosynthesis)
3. Nitrogen cycle: N2 to NO3 (atmospheric nitrogen to
plant utilizable nitrate) (process: N-fixation)
4. Nitrogen cycle: N2 to NH3 (plant utilizable ammonia)
(process: Haber-Bosch Industrial N-fixation)
5. Water cycle: Liquid water to water vapor (process:
evaporation and evapo-transpiration)
6. Water cycle: Water vapor to liquid water (process:
condensation)
Biogeochemical Cycle :
• chemical elements are required by life from the living
and nonliving parts of the environment.
• These elements cycle in either a gas cycle or a
sedimentary cycle
• In a gas cycle elements move through the
atmosphere.
• Main reservoirs are the atmosphere and the ocean.
• Sedimentary cycle elements move from land to water
to sediment.
Carbon Cycle
• What are the
2 main processes
in the carbon
cycle?
Carbon Cycle
• Carbon (C) enters the biosphere during
photosynthesis:
• CO2 + H2O (carbon dioxide+ water)--->
C6H12O6 + O2 + H2O(sugar+oxygen+water)
• Carbon is returned to the biosphere in cellular
respiration:
• O2 +H2O + C6H12O6 ---> CO2 +H2O + energy
Carbon Facts
• Every year there is a measurable difference in the
concentration of atmospheric CO2 with changes in
the seasons.
– For example, in winter there is almost no
photosynthesis ( higher CO2 )
– During the growing season there is a
measurable difference in the
concentration of atmospheric CO2 over
parts of each day.
Nitrogen cycle
Nitrogen Facts
• Nitrogen (N) is an essential constituent of
protein, DNA, RNA, and chlorophyll.
• Nitrogen is the most abundant gas in the
atmosphere.
• Nitrogen must be fixed or converted into a
usable form.
Oxygen Cycle (Photosynthesis)
Sources of Oxygen:
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Photosynthesis and respiration
Photo disassociation of H2O vapor
CO2 and circulates freely throughout the biosphere.
Some combines with Ca to form carbonates.
Some combines with nitrogen compounds to form nitrates.
Some combines with iron compounds to form ferric oxides.
Some in the troposphere is reduced to O3 (ozone).
Ground level is a pollutant which damages lungs.
Phosphorus
(P) Cycle
Phosphorus (P) Cycle
Component of DNA, RNA, ATP, proteins and enzymes
- Cycles in a sedimentary cycle
- A good example of how a mineral element becomes part of an organism.
- The source of Phosphorus (P) is rock.
- Phosphorus is released into the cycle through erosion or mining.
- Phosphorus is soluble in H2O as phosphate (PO4)
-Phosphorus is taken up by plant roots, then travels through food chains.
- It is returned to sediment
Sulfur (s) Cycle
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Component of protein
Cycles in both a gas and sedimentary cycle.
The source of Sulfur is the lithosphere (earth's crust)
Sulfur (S) enters the atmosphere as hydrogen
sulfide (H2S) during fossil fuel combustion, volcanic
eruptions, gas exchange at ocean surfaces, and decomposition.
• SO2 and water vapor makes H2SO4 ( a weak sulfuric acid),
which is then carried to Earth in rainfall.
• Sulfur in soluble form is taken up by plant roots and
incorporated into amino acids such as cysteine. It then travels through the
food chain and is eventually released through decomposition.
Summary
• The building blocks of life :Water ,Nitrogen, Carbon
Dioxide, Phosphorus, Sulfur
• Continually cycle through Earth's systems, the
atmosphere, hydrosphere, biosphere, and
lithosphere, on time scales that range from a few
days to millions of years.
• These cycles are called biogeochemical cycles,
because they include a variety of biological,
geological, and chemical processes.