Ch 23 Ecosystems Flashcards
Define Ecosystem
All living organisms that interact with one another and the abiotic conditions in an area
Examples of Abiotic factors affecting Ecosystems
Light intensity Temperature Water Availability/content of soil Edaphic (Soil) Factors - Clay, Loam, Sand Oxygen Availability
Examples of Biotic factors affecting Ecosystems
Interspecific Competition
Intraspecific Competition
Predation
Disease (bacterial/viral)
What is a trophic level?
a stage in the food chain
Rarely +4 levels since there is not sufficient biomass/energy left to support any further organisms as less biomass at each successive level.
what is the Order of Trophic Levels?
Producer
Primary Consumer
Secondary Consumer, Tertiary Consumer
What are Decomposers?
Describe role of decomposers in food webs.
Organism that Feeds on Dead plant/animal (Organic matter), Breaking it Down into Nutrients (inorganic), to be released back into the ecosystem, available to photosynthetic producers.
Saprotrophic nutrition - extracellular
What is Biomass?
= Mass of Living Material present in a particular place or organism.
Biomass is an important measure of food chains as it can be equated to energy content.
Biomass at Trophic level (Calculation)
Biomass at Trophic level =
= Biomass present in each organism X Number of organisms in the trophic level
How to Calculate “Dry Mass”
Collect and Kill organism Sample
place in 80 degrees C Oven, untill all Water has Evaportated - indicated by at least 2 identical mass readings
Minimise distruction of organisms by only taking a small sample
! Sample may not be Representative of the whole population!
The biomass in each trophic level is always less than the trophic level below; Why?
Biomass = all cells & tissue of organism (incl. bones/ feathers)
bones/feathers not eaten = some biomass not transfered
Only a Small Propotion of food ingested is Converted into New Biomass
- most used for reactions, or egested in feaces and urine
hence it is only this that is available in the next trophic level
energy available at a trophic level units
Kilojoules per metre squared per year
KJm^-2 yr^-1
Define ‘Ecological Efficiency’
Ecological Efficiency = the Efficiency with which Biomass or energy is Transferred from One Trophic Level to the next.
Why do Producers only convert 1-3% of sunlight recieved into Chemical Energy?
(Efficieny at Producer level)
Not All solar energy available is Used for Photosynthesis - 90% is Reflected, Some is Transmitted, and some is of Unusable Wavelength
Other factors Limit photosynthesis, eg. water
A proportion of energy is ‘lost’ - used for Photosynthetic reactions
Define ‘Gross Production’
Gross production = total light energy converted to chemical energy by plants Organic Matter (20-50% used in respiration, and remaining is converted to Biomass = net production)
Define ‘Net Production’
Gross production - Respiratory losses
Gross production = total energy converted by plants from light energy to chemical energy
Why do Consumers only convert 10% max. of biomass eaten to Organic tissue?
(Efficiency at Consumer level)
Some energy transferred to environment as metabolic heat (movement & respiration)
Some parts of food are ingestible so are egested in faeces
Some energy is lost in Urine
Ecological Efficiency (formula)
Energy/Biomass available After transfer
————————————————————- X 100
Energy/Biomass available Before transfer
How human activities manipulate Biomass through Ecosystems
Plants/Animals are provided with the Abiotic Conditions they need to thrive: water, warmth (greenhousing/ stabling)
Competition from other species is removed (pesticide)
Agriculture creates Simple Food Chains
Why?
Producer (Animal Feed) > Primary Consumer (Livestock) > Secondary Consumer (Humans)
To minimise energy lost through transfers between trophic levels, ensuring as much energy possible is transferred into biomass to be eaten by humans.
What is Decomposition?
Chemical process in which a Compound is Broken down into Smaller molecules or its Constituent Elements.
Often elements cannot be used by organisms in an organic form, so it must be processed into more usable inorganic elements and compounds.
Define Saptrophic nutrition (by a Saprotroph)
Saprotroph = organism that Feeds on Decaying matter
Involves Extracellular Digestion in processing decayed organic matter
What are ‘Detritivores’?
Class of Organism involved in Decomposition.
Speed decaying process by feeding on detritus - dead, decaying material - by breaking it down into smaller pieces of organic material, increasing the surface area for decomposers to work on.
Internal Digestion
Woodlice & Earthworms
What form of Nitrogen can plants absorb?
Ammonia, NH3
produced by Nitrogen Fixation
Nitrogen Fixing Bacteria
Azobacter = free-living soil bacterium Rhizobium = lives in root nodules on leguminous plants, have a 'Symbiotic Mutualistic Relationship'
Rhizobium:
Features of the Symbiotic Mutualistic Relationship between Rhizobium and Leguminous plants
Plants - gain Amino Acids from Rhizobium, produced by fixing the nitrogen gas into ammonia, NH3
Bacteria - gain Carbohydrates produced by Plant in Photosynthesis, as an energy source
What is Nitrification?
Nitrification = ammonium compounds in the soil are converted into nitrogen-containing molecules that can be used by plants, by Nitrifying Bacteria.
Oxidation reaction
Nitrosomas - oxidise Ammonium compounds into Nitrites (NO2-)
Nitrobacter - oxidise Nitrites (NO2-) into Nitrates (NO3-)
Nitrate NO3- are highly soluble = enter plant
What is Denitrification
Denitrifying bacteria convert Nitrates in the soil to Nitrogen gas (N2)
Anaerobic conditions/Absence of O2, e.g. watterlogged soil
What is Ammonification
Ammonium compounds released into atmosphere from NH group
What are Rhizobium and Azobacter involved in?
Nitrogen-Fixing (N2-NH3)
= ammonium
What are Denitrifying bacteria?
Anaerobic, involved in Denitrification (Nitrates - N2 gas)
What are Nitrosomas and Nitrobacter involved in?
Nitrification:
Nitrosomas = ammonium compunds —> Nitrites
Nitrobacter = Nitrites —> Nitrates
What is Combustion
Burning fossil fules (carbon-containing compound), releasing trapped CO2 into atmosphere
What is Decomposition (carbon cycle)
Decomposers break down dead, decaying organisms, releasing CO2 into atmosphere
Role of Death of organisms in Carbon Cycle
carbon compounds in dead organisms are released back to atmosphere through decomposition, from store as organic matter
Carbon Dioxide levels fluctuate throughout the day, why?
Photosynthesis (uses CO2) only happens during the day in the light.
Respiration (releases CO2) happens all day regardless, releasing CO2 at a relatively constant rate.
= Atmospheric Carbon Levels Higher during the NIGHT
Lower in summer than winter (more photosynthesis)
Global Atmospheric Carbon levels have increased over the past 200 years, due to:
Combustion of Fossil Fules; releasing previously stored CO2 into atmosphere.
Deforestation; Removes significant photosynthesising biomass from earth.
What causes Global Warming?
Increased levels of CO2
= Greenhouse gas effect; more Thermal Energy trapped in the Atomosphere (GHG) - atmosphere traps more radiation = warms
warmer = less CO2 dissolves
Effects of Global Warming
Higher Temperature = Less CO2 Dissolved (reducing carbon bank, so more CO2 is released; Positive Feedback Loop
Define ‘Succession’
Process by which ecosystems change over time.
occurs in result of changes to the environment (abiotic), causing the plant & animal species to change.
Primary & Secondary Succession
Primary Succession
ecological succession that begins in lifeless areas like Newly Formed or Exposed land, e.g. bare rock.
No soil or organic material
When Volcanos erupt depositing Lava, New Sand Dunes, Silt and Mud deposits at Estuaries, Glaciers Retreat, depositing rubble and exposing rock.
Secondary Succession
ecological succession where organisms Recolonise land where Soil is present but contains No animal or plant species.
e.g. bare earth after forest fire
Define what is meant by a ‘Seral Stage’ or ‘Sere’
a step/stage of succession
At each Seral stage key species are identified that change abiotic factors (soil = more fertile)
What are the main Seral Stages
Pioneer community - Colonisers, e.g. lichen
Intermediate community
Climax community - Dominant species, e.g. woodland
Primary Succession begins with a Pioneer Community
Features:
Pioneer species colonise an inhospitable environment, arriving as spores/seeds carried by wind, e.g. Algae & Lichen
ADAPTATIONS: germinate rapidly, Photosynthetic
produce lots of seeds/spores (to be blown by wind)
tolerance to extremes
Can fix Nitrogen = add nutrients to soil
Intermediate Community:
1
2
3
weathering of rock produces basis of soil. Dead/decomposing pioneer species = humus = organic component of soil.
Soil is now able to support growth of new species; Secondary Colonisers (contains minerals)
Tertiary Colonisers, fern - dont need abundance of water
Soil nutrients content increases = more fertile
Final Seral Stage:
Climax Community
Community is in a stable state
few dominant species - outcompete others
NOT most biodiverse
Animal succession
Slower than plant succession
Primary Consumers - insects, worms
Secondary Consumers -
Larger organisms - mammals and reptiles
What is Deflected Succession?
Human activities can halt the natural flow of succession and prevent an ecosystem reaching a climax community.
when succession is stopped artificially, a plagioclimax is formed.
What is ‘Plagioclimax’
a Plagioclimax is the Final stage formed when Succession is Stopped Artificially/Deflected
Examples of Deflected Succession
Grazing & Trampling of vegetation by animals = grassland
Removing existing vegetation (shrubland) to plant crops
Burning to clear forests - provides nutrient-rich ash for other species to grow; increasing biodiversity
What is meant by ‘Distribution’ of organisms?
The distribution of organisms refers to Where individual organisms are found within an ecosystem.
usually uneven throughout - organisms are generally found where abiotic & biotic factors suit them; they have a better chance of survival as have all resources
How to measure Distribution of organisms within an ecosystem
Line Transect:
lay surveyor’s tape along ground, taking samples at regular intervals
Belt Transect (provides more info):
2 parallel lines marked and samples taken of area between.
Both systematic, non-random sampling = allows Study of How Differing Abiotic Factors in Different Areas of the habitat Affect Distribution of Species
What is meant by the ‘abundance’ of organisms?
Number of individuals of a species present in an area at any given time. Fluctuates daily;
Immigration & Birth Increases Abundance
Emigration & Deaths Decrease Abundance
How to measure Abundance of organisms / population
Estimate using Sampling Techniques
a sample is Never entirely Representative of the organisms present in a habitat - use Larger Sample Size to increase Accuracy, and Random Sampling to eliminate Bias.
Counting all members would be too Time Consuming, Difficult and may Damage the Environment.
Measuring Plant Abundance
Place Quadrats Randomly in area.
Count number of indiuvidual plants within
= Abundance of organisms in quadrat
estimate abundance of plants in area (m^-2):
area of sample
Estimated number in population
m^-2
Area of Sample
Measuring Animal Abundance
Capture-Mark-Release-Recapture
Capture-Mark-Release-Recapture
- Capture as many individuals possible in sample area
- Mark/tag each individual
- Release animals back into area & allow time for redistribution
- Recapture as many individuals possible in same area
- Record number of Marked & Unmarked individuals present in the sample. Release animals.
- Use Lincon Index to Estimate Population Size
Simpson’s Index of Diversity
used to calculate biodiversity present in habitat
0-1; higher = more diverse
what is Sampling?
Method of Estimating Number of Individuals of each species in a Habitat
