ecosystems
ecosystem
biological community of interacting organisms and their physical environment
biotic factors
predators
Availability of food
Competition (Interspecific-variation between different species and intraspecific-variation within a species
Disease
Decomposers
abiotic factor
Light intensity
Temperature
Water availability
Soil pH
Oxygen and carbon dioxide concentration
why are ecosystems dynamic?
They are constantly changing due to different seasons and events
biomass
Mass of living material present in a particular place or organism
trophic level
Each stage in a food chain
dry mass
More reliable
process of measuring dry mass
1. Collect samples from each trophic level
2. Dry the organisms in an oven
3. Calculate dry biomass per unit area
4. Multiplied by area to get total biomass
units used
Land- kgm^-2 yr^-1
Water- kgm^-3 yr^-1
Energy- kJm^-2 yr^-1
ecological efficiency
Efficiency with which biomass or energy is transferred from one trophic level to the next
net production
Gross production-respiratory losses
ecological efficiency Equation
Energy or bio mass after transfer/Energy or bio must before transfer x100
The fewer trophic level
The more efficient because energy is lost at each trophic level
why do food chains rarely have more than four trophic levels?
There is not a sufficient biomass and stored energy left to support any further organisms
why is the energy loss of each trophic level?
Respiration
egestion
Excretion
Not all parts are eaten
how humans aim to increase efficiency
Selective breeding- faster growing animals/plants
Animal farming
Controlled feeding- more easily digestible food
Use of fertilisers and pesticides
nitrogen fixation
Nitrogen gas (N2) -> Ammonia (NH3) or ammonium ions (NH4+)
reduction reaction
azotobacter (in soil)
rhizobium (in root nodules)
ammonification
Decomposers convert organic nitrogen compounds from dead organisms into ammonia
(NH3) -> ammonium ions (NH4+)
nitrification
nitrosomonas: NH4+ -> NO2- (nitrite)
nitrobacter: NO2- -> NO3- (nitrate)
oxidation reaction
denitrification
nitrates (NO3-) back to nitrogen gas (N2)
in waterlogged soil
reduction reaction
carbon dioxide %
0.04%
photosynthesis
plants and algae absorb co2 from atmosphere
respiration
carbon compounds are broken down releasing co2 into atmosphere
decomposition
microorganisms break down dead organisms releasing co2 via respiration
combustion
burning fossil fuels and biomass releases co2
Fossilisation
Dead organisms form fossil fuel fuels
human impact on carbon cycle
Increased combustion of fossil fuels
Deforestation
Soil disturbance
succession
Gradual change in the structure and species composition of an ecosystem overtime
three types of succession
Primary- Ben newly formed or exposed such as bear rock or sand
Secondary- Areas of land where soil was present but contains no plant or animal species
Deflected- Human intervention prevents the final stage of succession occurring e.g. garden
stages of succession
1. Pioneer species colonise habitat E.g. lichens
2. The species changed the environment
3. Soil builds up allowing more complex plants to grow
4. With more vegetation, animal start to appear
5. Eventually, climax community is reached (Stable mature ecosystem)
characteristics of pioneers species
Tolerate extreme Condition
Can photosynthesise
Can reproduce rapidly
Can fix Nitrogen
difference between climax community and plagioclimax
p- Artificial
c- Natural
measuring Plant abundance
Quadrats are placed randomly in an area
Estimated number in population= Number of individuals in the sample/Area of sample
measuring animal abundance
Capture mark release recapture technique
1. Capture as many animals as you can
2. Count them and mark them
3. Release them
4. Capture same species
5. Count how many are marked
pop size= no in 1st x no in 2nd/no in 2nd previously marked
assumptions to be made
No death
No migration
Identical sampling methods
important considerations
Controlled time of day, weather and season
use standardised methods
Repeat to improve reliability
Use random number generators for random sampling
ACFOR scale
A- abundant (Very common)
C- common (Frequently found)
F- frequent (Fairly often)
O- occasional (Present, but not often)
R- rare (Seldom seen or found only once)
advantages of ACFOR
Fast and quick
Minimal tools require required
limitations of ACFOR
Subjective
Hard to standardise
Not Quantitative