Ecosystems

Ecosystem - a distinct, self-supporting system of organism interacting with each other and with the physical environment. It includes all of the organisms living that interact with a defined region and all of the physical factors present in that region.

It's components are:

• A habitat
• A population - all organisms found of a particular species found in an ecosystem at any one time
• A community - populations of all species found in a particular ecosystem at one time

Ecosystems are describes as dynamic - constantly changing as a result of interactions between living organisms and their environment, causing population size fluctuations which will affect other populations.

Abiotic - non-living factors e.g. edaphic factors such as pH, humus, particle size, mineral content.
Biotic - interactions between organisms that live or have lived e.g. competition such as food, territory, breeding partners.

Biomass - the mass of living organisms present in a particular place or in a particular organism.
Measuring biomass- mass of carbon or dry mass of tissue per given area per given time
Measuring energy- chemical energy store in dry biomass using bomb calorimeter

Biomass at tropic level = biomass of each organism x total number of organisms
Net production = gross production - respiratory losses
Efficiency of transfer = (net productive of tropic level / previous trophies level) x 100

An organism's tropic level shows which level of the food chain they occupy e.g. producers, primary secondary and tertiary consumers, decomposers

Efficiency at producer level:
90% reflected as not a usable wavelength or is transmitted through leaves, limiting factors of photosynthesis, lost in photosynthetic reactions
Efficiency at consumer level:
Some not eaten or are indigestible, transferred to environment as metabolic heat, lost in excretory materials

• Agriculture favours specific plants (monoculture) - manipulating environment with abiotic conditions plant needs to thrive and removal of predators
• Intensive farming - energy mostly used for growth
• Primary productivity increased - greenhouses and light banks, genetically modified plants
• Secondary productivity increased - havesting young animals as invest larger proportion of energy into growing, selective breeding, treating animals with antibodies, zero grazing
• Herbicides - kill weeds that compete with agricultural crops for energy
• Fungicides - kill fungal infections that damage agricultural crops
• Insecticides - kill priests that eat and damage crops
• Introduction of natural predators that eat the pest species
• Ferilisers - chemicals provide crops with minerals needed for growth
• Creating simple food chains - minimal energy loss

Succession - proccess by which an ecosystem directional changes causing plants and animals species to change overtime (biotic conditions change as a result of abiotic conditions changing).

Types of succession:

1) Primary - areas of land that are newly formed or exposed e.g. bare rock and have no soil or organic material to begin with.

2) Secondary - areas of land that have been cleared of all plant and animal species e.g. by forest fires where soil is still present.

At each serial stage in succession, species are better adapted so outcompete previous species and become dominant, changing both abiotic and biotic factors of the ecosystem.

Pioneer community:

• colonisation of inhospital environment by species arriving as spores or seeds from nearby land mosses, by wind or animals droppings e.g. lichens or algae
• in secondary succcessions species are often shrubs
• species stabilise environment to allow further growth and microorganisms decompose their dead organic material to form basic soil that retains water and adds minerals

Intermediate community:

• secondary colonisers e.g mosses arrive as spores or seeds
• environmental conditions improve and allow tertiary colonisers
• rock continues to errrode
• more death so more nutrients-rich soil retaining more water
• coloniser plant species provide food so that primary consumers to move in

Climax community:

• favourable stable biotic conditions allow larger organisms to move in
• little change over time
• climax not always most biodiverse as dominant species outcompetes others

When succession is stopped artificially from reaching it's normal climax community, the climax community is called plagioclimax.

Deflected succession is when succession is prevented by human activity, but the plagioclimax that develop is one that's different to any of the natural stages of the ecosystem - the path of succession has been deflected from its natural cause.

Decomposers:
-macroscopic fungi and bacteria (saprothrophs - obtain energy from dead/decaying material)
-External digestion by secreting enzymes onto dead organisms/waste materials to break them into smaller molecules which can be absorbed back into an organism's body as inorganic small soluble molecules (so available for photosynthesis)

Detritivores:
-e.g. earthworms (heterotrophs - obtain food from environment)
-break detritus into smaller pieces of organic material to increase the surface area for decomposers
-speed up process of decomposition

Nitrogen fixation - combining atmosphere N2 with H2 to produce NH3 that can be used by plants using nitrogen-fixing bacteria containing nitrogenase (or lightening):
-Azobacter - free living soil bacterium
-Rhizobium - living inside root nodules with a symbiotic mutualistic relationship (amino acids to plants and carbohydrates to bacteria)

Ammonification - decomposers convert nitrogen containing compounds, found in faeces, urine and dead organisms, into ammonium compounds:
-Nitrogen Reductase reduce nitrogen to NH4+ ions under anaerobic conditions (leghaemoglobin protein absorbs O2 in nodules)

Nitrification - NH4+ converted into nitrogen containing molecules by oxidation in aerated soil by nitrifying bacteria (chemoautotrophic - make own energy with chems):
-Nitrosomas - converts ammonium ions into nitrites NO2-
-Nitrobacter - converts nitrites into nitrates NO3- (or put in using fertilisers)

Dentrification - nitrates converted back into nitrogen in gas under anaerobic conditions by dentrifying bacteria (using nitrates as energy source for respiration).

Returning carbon to air:
-Decompositon
-Respiration
-Volcanic eruptions
-Weathering
-Combustion
-Relsease from ocean

Carbon entering ecosystems:
-Photosynthesis
-Reabsorbtion into ocean

Carbon transferred through ecosystem:
-Decomposition (saprobiontic nutrition - decomposers feeding on dead organic matter)

Distribution - where individuals are found within an ecosystem:
-Line transect - regular intervals
-Belt transect - imbetween two parallel lines

Abundance - number of individuals of a species present in an area at a given time:
-Quadrats - estimated no. in population = no. of individuals in sample/area of sample
-Capture-mark-release-recapture (Lincoln index) - (no. in 1st x no. in 2nd)/no. of recaptured marked individuals

Distribution - where individuals are found within an ecosystem:
-Line transect - regular intervals
-Belt transect - imbetween two parallel lines

Abundance - number of individuals of a species present in an area at a given time:
-Quadrats - estimated no. in population = no. of individuals in sample/area of sample
-Capture-mark-release-recapture (Lincoln index) - (no. in 1st x no. in 2nd)/no. of recaptured marked individuals