Ecology definitions
1. Ecosystem – a group of populations of organisms interacting together in a specific environment
e.g....
Energy flow through an ecosystem. - Energy cannot be recycled. It enters through the producers as
light energy and they tr...
http://www.google.com/imgres?imgurl=http://web1.stmaryssen-h.schools.nsw.edu.au
1. Use the total numbers at each trophic l...
Nutrient cycles
The raw materials needed by an ecosystem are recycled, for example, CO2 released by animal
respiration is ...
S The Nitrogen Cycle
Plants absorb soil nitrate and convert it to protein. Their protein can either be ingested by herbivo...
Population Size
The main factors affecting the size of a population are
Food supply – Resources are plentiful in a small p...
Human population growth
is in the exponential phase and therefore the population requires ever-increasing resources. This ...
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Ecology Revision Notes

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Ecology Revision Notes

  1. 1. Ecology definitions 1. Ecosystem – a group of populations of organisms interacting together in a specific environment e.g. a lake. 2. Producer - an organism that makes its own organic nutrients from inorganic raw materials using an energy source, usually the sun. 3. Consumer – an organism that gains energy and organic nutrients from eating other organisms. 4. Herbivore – an organism which gets its energy from eating producers (plants) 5. Carnivore – an organism which gains its energy by eating other animals 6. Decomposer – an organism that gains its energy from dead or waste organic matter. 7. Food chain - a chart showing the flow of energy from one organism to the next, beginning with a producer and ending with a carnivore Rose → Aphid Blackbird Sparrow Hawk 8. Food web - a network of interconnecting food chains showing the energy flow through an ecosystem. Fox grass snake blackbird toad rabbit squirrel grasshopper vegetation 9. Trophic level – the position of an organism in a food chain, web or pyramid. vegetation 1st trophic level (producer) 1st order consumer snail 2nd trophic level (herbivores only) 2nd order consumer thrush 3rd trophic level (omnivores, carnivores) 3rd order consumer cat 4th tropic level (usually carnivores) supercarnivore 10. Population – a group of organisms of one species living in the same area at the same time.
  2. 2. Energy flow through an ecosystem. - Energy cannot be recycled. It enters through the producers as light energy and they transform it to chemical energy which passes up the food chain. An ecosystem therefore needs a constant supply of energy. Only about 10% of the energy available at one trophic level is available to the next. This is because o Animals and plants use energy for respiration. o Not all the food that is eaten is digested. o Some substances are excreted S This means that food chains rarely exceed 5 links and populations of supercarnivores are small. S The human population is more easily sustained by eating at the 2nd trophic level as there is more energy available. At this level than the amount available from eating meat (about 18kg of grass is needed to produce 1 kg of meat) Ecological Pyramids Pyramid of numbers. A pyramid, drawn to scale, shows the population present in a community or food chain at each trophic level. Can be inverted if the producers are large e.g. forest (trees) Pyramid of biomass A pyramid, drawn to scale, shows the mass of the population (population x average mass of individual) present in a community or food chain at each trophic level. Can be inverted if the producers reproduce sufficiently quickly. Aphids Trees Blackbirds Aphids Trees Blackbirds 15,476 Aphids x 0.4g = 6190g = 6.19Kg biomass
  3. 3. http://www.google.com/imgres?imgurl=http://web1.stmaryssen-h.schools.nsw.edu.au 1. Use the total numbers at each trophic level and draw a pyramid of numbers on graph paper. Use a scale of 1cm representing 100 organisms in the population. 2. Given the following masses of the organisms present, complete the table and draw to scale a pyramid of biomass for the same organisms using a suitable scale. Organism Average mass of one organism g. Population Biomass Size to scale on pyramid Plants 11.2 Worm 4.5 Snail 6.6 Thrush 125.0 Blackbird 105.5 Sparrow Hawk 248.0 3. What happens to the size of a step in the pyramid at each trophic level? 4. If the pyramids were drawn for a forest ecosystem would they appear different? Population in ecosystem 2 sparrow hawks 11 thrushes and 9 blackbirds 620 snails and 560 worms 6450 plants
  4. 4. Nutrient cycles The raw materials needed by an ecosystem are recycled, for example, CO2 released by animal respiration is utilised in plant photosynthesis, converted to glucose and then could return to a herbivore when it eats the plants. The same applies to all raw materials including minerals, oxygen and water. The flow of these nutrients in ecosystems is known as a nutrient cycle. Carbon Cycle CO2 enters the atmosphere through respiration and is absorbed by plants for photosynthesis. Animals then eat the plant carbohydrates, oils, proteins and organic carbon passes up the food chain. Combustion of fossil fuels and wood also adds CO2 to the atmosphere Labels for arrows: Decomposition, combustion, fossilisation, photosynthesis, respiration, excretion/death, digestion and assimilation. (some arrows can be used twice) Notes: 1. Most CO2 is found in atmosphere – around 0.04%, rising to 0.045% at night and dropping to 0.038% in daytime (depending on the season) due to changes in photosynthesis rates. 2. As seasons and day/night are in apposition, the overall atmospheric level is balanced 3. Combustion of fossil fuels and deforestation has added approximately 0.005% more CO2 to the atmosphere in the last 50 years and the rise is increasing, contributing to global warming. The Water Cycle Notes Addition of water to the atmosphere by evaporation from seas, lakes, rivers and transpiration from plants leads to the formation of clouds by condensation. The clouds return water to the ground by precipitation (rain) and the water is absorbed by plant roots or enters soil or river, lake sea water. Loss of forests lowers transpiration and therefore local rainfall (as well as leading to soil erosion and contributing to atmospheric CO2 increase). Carbon dioxide in air and dissolved in water Plant organic carbon e.g. sugar, protein Animal organic carbon e.g. sugar, fat Saprotroph organic carbon Fossil fuels e.g. coal, oil, gas
  5. 5. S The Nitrogen Cycle Plants absorb soil nitrate and convert it to protein. Their protein can either be ingested by herbivores and pass up the food chain or, on death, leaf fall, broken down by saprotrophs to decay products in the soil. Animal excreta, egesta and dead remains are also broken down by saprotrophs to decay products in the soil. Nitrifying bacteria then convert these decay products back to nitrate to be re-used by the plants. Denitrifying bacteria use up nitrate to gain oxygen, nitrifying bacteria make nitrate from atmospheric nitrogen Additional notes 1. Lightning can cause N2 (air) to react with O2 + H2O to form Ammonia, which dissolves in clouds and comes to soil in rain. 2. Nitrification. Animals excrete urea, ammonia (NH4 + ) is formed by saprotrophs and both are useless to plants. They are oxidised by nitrifying bacteria to NO3 - (Nitrate) which can be absorbed by plant roots and converted to protein. The plants are then eaten by animals which manufacture animal protein. 3. Farmers add nitrate and ammonia fertilisers to soil (the amount of NO3 - in soil determines how much protein plants can make and therefore how fast they can grow). 4. Some nitrogen-fixing bacteria can fix atmospheric nitrogen, converting it directly into nitrate. Some live freely in soil, some live in root nodules of plants of the Pea family (hence growing peas and beans and clover in a crop rotation which is a natural way to increase soil nitrogen). The pea plant symbioses with the bacteria -- the plant supplies sugars and the bacteria supplies nitrates, both benefit by the association. 5. Leaching -- both ammonia and nitrates are highly soluble and so can be washed out of the soil by rain, the use of nitrate fertilisers increases the population of denitrifying bacteria 6. Denitrification - denitrifying bacteria change NO3 - to N2 which leaves soil for the atmosphere. Place all the words in bold on the correct arrows in the cycle above. N as products of decay in the soil (urea, ammonia) N2 in atmosphere N as protein in animals N as protein in plants N as NO3 - (nitrate) in soil Fertilisers
  6. 6. Population Size The main factors affecting the size of a population are Food supply – Resources are plentiful in a small population with little competition and/or at a favourable time of year. They may be scarce in winter. Predation – as the supply of prey increases, the predator population will increase and probably reduce the prey population. The predator prevents the prey population from overexploiting the ecosystem. Disease – can be fatal in both animals and plants. It is more common in crowded conditions (as transfer from one organism to another is easier) and more fatal in populations weakened by lack of food When there is a natural balance within a community in terms of the physical and living components, a stable population is maintained. For a theoretical population, the Sigmoid growth curve normally applies when there are limited resources and therefore competition for raw materials. It has three phases as the population reaches maturity: S The phases of the growth curve are S Explain the three phases of the curve for the following populations: Population Explanation of Phase Lag Exponential Stationary Bacteria introduced into sterile milk Rabbit population over a Spring and Summer Replanted forest x Lag phase Sigmoid Growth Curve of a Population Exponential phase Stationary phase Population size Time Lag – establishment, finding resources, preparation for reproduction before the population grows. Exponential – resources are abundant, disease and predation low allowing a very fast increase in population. Stationary– resources match population and the checks provided by predation, disease, emigration, immigration give a stable, mature population where birth and death rates are equal. (Death – if the population overexploits the resources.)
  7. 7. Human population growth is in the exponential phase and therefore the population requires ever-increasing resources. This leads to: 1. Habitat destruction for building and farming 2. Increased carbon dioxide emissions and 3. Global warming http://www.prb.org/ is an interesting site on world human population. http://ecology110armine2011sp.files.wordpress.com/2011/05/population_growth.jpg

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