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Ecosystems
Ecosystem
Community
Population
Species
Environment
Habitat
Niche

A community of organisms and their physical environment with its particular abiotic
factors
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All the organisms belonging to all the species that coexist in the same habitat and
interact together
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The group of organisms of the same species which live in, or occupying the same
defined area at the same particular time
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They are reproductively isolated from other groups
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Particular geographical area occupied by a population with particular abiotic factors
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(Physical
space occupied, role carried out within the community and interrelationships with
other species
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The Earths
surface also reflects 90% of the light by vegetation, soil and water or absorbed and radiated into
atmosphere as heat
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The amount of energy
available is reduced at each level which limits length of food chain
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 Producers lose energy via respiration in the form of heat, death
 Herbivores lose energy via respiration in form of heat, death, egestion, defaecation
 Carnivores lose energy via respiration in the form of heat, egestion, defaecation
 Detritus is broken down by decomposers and detritivores use the dead matter to respire
Decomposers and Detritivores;
 Energy is locked up in organic compounds of dead producers and consumers
 Decomposers and detritivores feed saprophytically and recycle nutrients
 Energy utilised and released as heat energy during respiration
Gross Ecological Efficiency
 Percentage energy at one trophic level which is incorporated to the next trophic level
 Rate at which energy passes into animals at each ~10% energy entering previous energy
level
 Varies in different ecosystems- oceanic are best, lowest is terrestrial involving birds and
mammals
Biological Productivity
 Rate at which biomass is produced in an ecosystem
 Biomass= Dry weight of organic matter comprising a group of organisms in a particular
habitat
 Primary Productivity- Rate at which new organic matter is formed by plants
 Secondary Productivity- Rate at which new organic matter accumulates in consumers
Primary Productivity;
 Gross Primary Productivity (GPP) is the rate at which the products of photosynthesis are
formed
 Net Primary Productivity (NPP_ is rate at which products accumulate as a large proportion of
gross production is respired
NPP= GPP-R
Secondary Productivity;
 Some NPP is unable to be used by consumers
 Herbivores have lower secondary productivity than carnivores

Herbivores;
 Eat grasses and weeds but not root or shoot system
 Material which cannot be digested (Cellulose) is egested
 Symbiotic microbes consume energy
 66% energy lost in faeces and urine
 Only part of NPP available is transferred to primary consumers
Carnivores;
 Protein rich diet- more readily and efficiently digested
 Only 20% energy intake lost in faeces and urine
 Absorb ~twice as much energy per unit mass of food than herbivores

The curve is a sigmoid curve
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g
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 Population reached maximum size which is carrying capacity for the particular environment
in which population occurs which is limit for number of each species
Death Phase;
 Numbers drop where death rate is greater than birth rate
 May occur when all food in a nutrient solution has been used up, toxic waste products
accumulated or disease

Succession
Process in which communities of plant and animal species are replaced in a particular are over time
by a series of different (and usually more complex) communities
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g
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g
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g
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g
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g
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g
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The overall size of a population is often dynamic
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For a given species,
in a particular environment, there is certain equilibrium constant equilibrium population that the
environment can support
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If population rises above cc then mortality increases/ breeding reduced so population drops
If population drops below cc then factors limiting growth are relieved so population rises
Factors Which Affect The Size of a Population
 Factors which limit growth of a particular population are together called environmental
resistance; climate/ weather, seasonal changes, space, water, food, predation, vegetation,
competition, disease
 Some factors slow down population growth rate and some could cause a population crash
for example; food, competition, predation, volcanic activity, meteor, disease
Density Dependent Factors- Effect on death rate increases as size of population increases; more
organisms, more individuals effected
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Tectonic
activity, flood, drought, bushfire

Competition
Plants; Space, Water, Light, Minerals
Animals; Mates, Food, Water, Habitat
Interspecific completion is completion which occurs between different species
Intraspecific competition is competition which occurs within a species

Recycling Nutrients
Ecosystems have only a limited amount of chemical elements so life depends on the recycling of
nutrients
Carbon Cycle;
 Carbon dioxide added to air by respiration of animals, microorganisms and plants,
combustion fossil fuels
 Carbon dioxide is removed from the atmosphere by photosynthesis
 Carbon is passed through trophic levels
 Carbon released back into air from animals by respiration of detritivores
 Large amounts of organic matter are prevented from decaying due to anaerobic conditions

Changes in Biosphere;
Biosphere is layer of air surrounding the Earths surface
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 Results in less UV absorbed so;
-Increased temperature
-Increased UV radiation
Greenhouse Effect
 High energy solar radiation pass to Earths surface, much of this is reflected towards space as
heat, which greenhouse gases trap

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Carbon dioxide, Methane, Water Vapour, nitrous Oxide
Increase in Carbon Dioxide-Burning of fossil fuels
-Deforestation- Fewer trees to absorb carbon dioxide, burning of remaining
vegetation to prepare for cultivation, vegetation dies and decomposes- releasing CO2

Possible Effects
 Possible temperature increases during next 50 years have suggested 1
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 Putrefaction- Decay possesses convert organic nitrogen (protein dead organisms) into
ammonia
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 Nitrification- Ammonia formed in putrefaction is converted by nitrification via bitrites to
nitrates, the main absorbable form of nitrogen
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 Nitrogen Fixation- Atmospheric nitrogen can be converted into nitrogen compounds by
nitrogen fixing bacteria found free and in root nodules
 Denitrification- Nitrogen is lost from ecosystems by denitrification
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Nitrogen is found in amino acids from which proteins are made, also in nucleic acids
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Eutrophication
Eutrophication is a natural process where concentration of salts builds up in bodies of water
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The salts are mainly nitrates and
phosphates
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However sewage
and fertilisers are an additional source of these salts
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Nitrate is a major ingredient;
 May pose threat to human health
 Highly soluble and leach into ponds and rivers
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At this stage the water may become green and light cannot penetrate deeper
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They are then
decomposed by saprophytic bacteria thus creating a considerable biochemical oxygen
demand (BOD)
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Finally the anaerobic bacteria may reduce nitrate- nitrite which are toxic
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3 ppm in drinking water
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Effects of Human Activities;
Evolution is usually quite slow but human influence has created new selection pressures
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 Rats have now become resistant as dominant allele R at a single locus in rats confers
resistance
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K
-Homozygotes (RR) are resistant but require large amount of Vit
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K
 Example of heterozygotic advantage with Rr being advantaged- in each generation there will
be all three genotypes
 In the rat pop
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Reducing amount prescribed
reduces chance of bacteria becoming resistant
 Resistant gene may generate an enzyme which could break down the antiobiotic
 MRSA has developed resistance to many antibiotics- used in hospitals
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Humans determine alleles passed on to future generations and which are lost rather
than the environment
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Problem- Promotes
homozygosity so increases chance of harmful recessive gene expressing itself- greater risk of
double recessive individual occurring
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(Inbreeding depression)
 Outbreeding- Occurs by crossing of unrelated varieties
 Promotes heterozygosity
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Endangered Species;
Human activities affect the ecosystems- overfishing, urban development, hunting, industrial
processes, deforestation
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Extinction rates are now
1000- 10,000 times more than past at 1 species per million
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Decline in numbers of many animals;
-Loss of habitat
-Over hunting by humans
-Competition from introduced species
-Deforestation
-Pollution
-Drainage of wetlands
Many species may be an important human asset- potential source of food, useful chemicals, diseaseresistant genes
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Conservation;
 Conservation of species ensures the conservation of existing gene pools
 Ethical reasons- conserve potentially useful genes for future generations of humans as well
as survival of species itself
 Conservation is maintenance of the biosphere and the enhancement of biodiversity
Some of trees and shrubs in the rainforest have medicinal properties- incalculable loss
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Legislation has been introduced
to protect endangered species and to prevent over grazing, over fishing, hunting, collection of birds
eggs, picking and collection of wild flowers
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Conflicts can exist between production
and conservation
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 Increase in inorganic fertilisers – unforeseen biological effects- Eutrofication

People are now more aware of countryside- place to visit, animals and plants, conserve and source
of food
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Half of them have been cut down over last 30 years
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Help balance CO2 levels in atmosphere
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Global scale- contributes to global
warming
 Destruction of Natural Habitats- Reduction in biodiversity
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Removal of vegetation affects climate mainly by
reducing rainfall accelerating desertification
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-Removal on high slopes results in heavy rain sweeping exposed soil to flood plains
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Only removed by evaporation so becomes wetter
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 Coppicing
 Selective cutting- Felling only some of largest trees, leaving others in place
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 Long rotation time- Leaving forest before reharvesting it
 Efficiency can be increased-Planting trees optimum distance apart as close together would result in
intraspecific competition- tall and thin with poor quality timber
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Efforts are being made to conserve tropical rainforest’
Ecotourism- responsible travel to natural areas that conserves the environment and improves the
well being of local people
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Overfishing;
Pressure on fish stocks certain to intensify as human pop
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Global demand
doubled
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Fishing using nets is indiscriminate as any fish large
enough gets caught
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suffer
Prey pop
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Difficult to enforce days at sea, mesh size, area so less
successful
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Fish Farming
Fish can be bred and grown to maturity in ponds, lakes and managed enclosures in
esturaries where predation is reduced and food supplies are maintained
Rapid growth when fish grow in warm discharge from factories, plankton can be grown using
fertiliser

Cost
 Fish farms are densely stocked for financial reasons- disease spreads
 Antibiotics required to keep fish healthy
Organic Fish Healthy
 Weaken wild stocks if farmed fish breed with wild
 Pollution in the water and seabed

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Carnivorous fish- require fish food
High level dioxins and polychlorinated biphenyls



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