6.3.1 Ecosystems

What is an ecosystem

• Definition: A relatively self contained system including all the living organisms and the environment, interacting with each other

• Range in size

• Ecosystems are dynamic - as they change over time in response to environmental conditions and species interactions

• Types of changes that can affect population size in an ecosystem

  • Cyclic changes

  • Directional changes

  • Unpredictable/ Erratic Changes

What are Biotic factors

Factors that involve other living organisms e.g.

• Paratism

• Mutualism

• Competition

• Predation

• Disease

• Availability of food

What are abiotic factors

Factors that involve non-living components of the environment e.g.

• Edaphic Factors (factors relating to the soil)

• Atmospheric humidity

• Availability of inorganic ions

• Water supply

What is biomass

The total living mass in an organism or at each trophic level

What are cyclic changes

The changes repeat themselves in a rhythm (e.g. predator-prey)

What are directional changes

Changes go in one direction. Certain variables continue to increase or decrease

What are Unpredictable/Erratic changes

No rhythm and no constant direction (e.g. hurricanes and wildfires)

What is a tolerance curve

• A graphical representation to show how an organism’s survival, growth or reproductive success is affected by changes in specific environmental factors

• Some abiotic factors can be lethal at one extreme (e.g. toxicity and pollutants) which the graph will show

• On a tolerance curve, the organisms will survive, grow and reproduce within an optimum range

What are the components of an ecosystem

• Habitats: the place where an organisms lives

• Population: all of the organisms of one species, who live in the same place at the same time and breed together

• Community: all the populations of different species, who live in the same place, at the same time, and who interact with each other

• Niche: the role of each species in an ecosystem

How is biomass transferred

• When an organism is eaten, its biomass is transferred to the primary consumer

• The transfers between each trophic level can be measured by calculating the dry mass at each trophic level

• Efficiency of biomass transfer formula = biomass transferred/biomass intake) x 100

How to calculate dry biomass

• Collect all the organisms and put them in an oven at 80 degrees celcius to evaporate all the water

• Check the mass periodically. Once the mass stops decreasing all the water had been removed. Record the mass once it stops changing

This method is destructive to the ecosystem, so ecologists often measure wet mass and calculate the dry mass on the basis of previously published data

How much biomass do organisms take in and why

• Organisms convert 10% of biomass in their food to their own organic matter because:

  • Not eating all of the biomass of an organism or are eaten but are indigestible

  • Some energy being transferred to the environment (e.g. metabolic heat from respiration and movement)

  • Some energy is lost in excretory materials e.g. urine

• Means that there are little levels in a biomass pyramid as there is insufficient energy to support organisms beyond a few trophic levels

How do humans manipulate biomass transfers

• Agriculture manipulates the environment in order to increase the efficiency of the biomass transfers at each trophic level

• Plants and animals are provided with abiotic factors they need to survive

• Competition from other species is removed (e.g. weed killers)

• The threat of predators is removed (e.g. pesticides)

• Only very short food chains are created (two or three trophic levels)

What is gross production

• The total light energy that plants convert to organic matter

  • Some of this is used, remaining is converted into biomass which becomes available at the next trophic level

  • Energy available at the next trophic level can be calculated - net production = gross production - respiratory losses

How does efficiency at the producer level work

• Producers only convert a small % of light energy they receive into chemical energy - biomass

  • Other 90% is reflected

  • Other light is transmitted

  • Some is of an unusable wavelength

  • Some is used for photosynthetic reactions

How is primary productivity increased

• Manipulating light levels

• Irrigating. Roos and producing drought-resistant strains

• Manipulating temperature by growing plans in greenhouses

• Crop rotation increases nutrient levels

• Use of fertilisers

• Use of pesticides and producing pest-resistant strains

• Use of fungicides

How is secondary productivity increased

• Harvest animals just before adulthood

• Selective breeding

• Treating animals with antibiotics

• Restricting movement by supplying animals directly with food

• Control body temperature by keeping them indoors

What is succession

• Ecosystems are dynamic

• Sometimes they change from being very simple to being relatively complex - process is known as succession

• During succession, the biotic conditions factors and the abiotic factors change over time

What is primary succession

The development of a community from bare ground - stages include

1. The pioneer community - algae and lichens grow on bare rock

2. Erosion of the rock and a build up of dead, organic matter produces enough quality soil for smaller plants like mosses and ferns to grow

3. In a similar way, larger plants succeed the smaller plants, until a final, stable community is reached (climax community)

• In the early stages - abiotic factors are the most important

• In the later stages - biotic factors are the most important - especially competition

How can succession be deflected

• Deflected succession: When succession is stopped or interfered with (by human activity)

  • E.g. farmers adding fertilisers and using herbicides

• Plagioclimax: The resultant sub climax community that results when an area is held in a particular stage of succession

• Deflected succession can make it hard to decide if an area warrants preservation or conservation

What is abundance

The number of individuals of a species in a given area.

What is distribution

Where organisms are found within an ecosystem.

Name the parts of the carbon cycle

What is the carbon cycle

• Driven by photosynthesis, respiration, decomposition, combustion and physics and chemical processes

  • Animals, plants and microorganisms (décomposeurs) respire to release C02 (chemical) into the atmosphere

  • Plants use gaseous C02 - removes it from the atmosphere (terrestrial plants) or dissolved carbonates in photosynthesis + incorporate it into organic molecules in producers (aquatic plants)

• C02 dissolves in water to form carbonic acid (Chemical)

• Carbon also enters rivers and lakes from the weathering of limestone and chalk

• Combustion of fossil fuels emits C02 into the atmosphere

What is Saprotrophic decomposition

• Saprophytes secrete enzymes onto dead and waste material

• Enzymes digest the material into small molecules, which are then absorbed into the saprotrophs body

• The absorbed molecules are stored or respired to release energy

What is fixed nitrogen

• Nitrogen chemically combined with other elements so that organisms can use it

• Plants can use it to build biological molecules

What is the nitrogen cycle

• Nitrogen fixation: converting inert N(2) into ‘fixed’ nitrogen, e.g. ammonium ions (NH+4) & nitrate ions (NO2-a)

• Decomposition & ammonification: ammonium ions (NH+4) are released by bacteria during the decomposition of proteins in dead and waste organic matter

• Nitrification: Bacteria oxidise ammonium ions to nitrites (NO-2) and nitrites to nitrates (NO-3)

• Denitrification: converting nitrates back to nitrogen gas

What is nitrogen fixation

• The conversion of atmospheric N2 gas to a more reactive form e.g. ammonia or nitrate

• N2 is unreactive and cannot be used by organisms in this form - can be made more reactive by:

  • By living organisms

  • In the atmosphere: lightning strikes or UV radiation

  • The Harber process: synthesising ammonia using nitrogen and hydrogen

How do living organisms cause nitrogen fixation

• Can be done by prokaryotes and archaeans

  • e.g. Azotobacter & Rhizobium bacteria - nitrogen fixing bacteria found freely in the soil (non-symbiotic) & root nodules of leguminous plants (mutualistic relationship)

• For these organisms to convert N2 to ammonium ions they need: hydrogen, ATP, nitrogen reductase (aka nitrogenase)

What is nitrification

• Chemoautotrophic (produce energy via chemical reactions) bacteria e.g.Nitrosomonas in the soil.

  • They obtain their energy by oxidising ammonium ions into nitrites

• Nitrobacter obtain energy by oxidising nitrites to nitrates

• These are known as nitrifying bacteria

What is denitrification

• Denitrifying bacteria convert nitrate to nitrogen gas, which is returned to the air (reverse nitrogen fixation)

  • Work in anaerobic conditions

• Commonly found in sewage treatment plants, compost heaps and wet soils

What is assimilation

• The incorporation of nitrate (or ammonia) into organic molecules by living organisms

• Happens after fixation and nitrification - occurs once soil bacteria or lightning convert atmospheric nitrogen gas into ammonia or nitrates that plants can absorb

Name the parts of the nitrogen cycle / Draw the nitrogen cycle

A = Nitrogen in producers

B = Nitrogen fixation

C = Nitrogen gas

D = Absorption

E = Denitrification

F = Nitrate

G = Nitrification

H = Nitrogen fixation

I = Nitrite

J = Nitrification

K = Ammonium Compounds

L = Feeding

M = Nitrogen in consumers

N = Death & Excretion

O = Death

P = Ammonification

Q = Decomposers