• Another cause of diversity may be the creation of different habitats within a region by periodic disturbance

• A community that forms if the land is undisturbed and that perpetuates itself for as long as no disturbance arises is called the climax community. When this climax community is disturbed – either by natural forces or man-made activities such as floods and fires or removal and overexploitation respectively, it begins the process of returning to its original state by a process known as ecological succession that produces a climax community again.

• There exist two types of ecological succession: primary and secondary succession

• Primary succession takes place in a barren or lifeless land with limited soil or no soil at all (very slow process)

• Secondary succession is the series of community changes that takes place in disturbed areas that have not been totally stripped off their soil. It is the most widely occurring phenomenon than primary. It is important to note that ecological succession is a process that takes place over relatively long periods with secondary succession being the least with about a few years to a hundred (Arms & Camp, 87)

• The third cause of diversity of species within communities lies with the climate.

2.5 Ecosystem level

• 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

• 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).

• 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…

• 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

• 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

– 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:

• 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 • 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.