Principles of Ecology
Definitions
Ecology: the study of how living organisms interact with each other and with their abiotic
environment.
Abiotic Factors: non-living components of the environment.
Habitat: the organism place of residence to which it is adapted.
Population: a group of individuals of the same species living in the same area that interact and
interbreed with each other.
Community: interacting populations of different species living in the same area.
Ecosystem: a community of organisms and the habitat’s non-living components.
Biosphere: the global ecosystem - the Earth’s ‘layer of life’.
Environmental Factors Affecting Living Organisms
Biotic Factors: the effect of other living organism of the same or other species.
Abiotic Factors: the effect of non-living items of the organism’s habitat.
Climatic Factors: the effect of the average weather conditions over time, e.g., temperature, rainfall,
day length, humidity, wind, atmospheric pressure.
Edaphic Factors: the effect of soil conditions e.g. pH, aeration, porosity, water content, mineral
nutrients, humus, soil type.
Aquatic Factors: e.g. wave action, tides, submergence time, exposure time, salinity, oxygen
concentration, currents, sedimentation and light quality.
Nutritional Types of Organisms
Producer (Autotroph): makes its own food from inorganic materials.
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Photosynthesis: light is the energy source.
Chemosynthesis: energy released by chemical reactions is the energy source.
Consumer (Heterotroph): cannot make food - uses ‘ready-made’ food.
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Herbivore: plant eating animal e.g. rabbit, honey bee, green fly.
Carnivore: flesh eating animal e.g. fox, hawk, ladybird.
Omnivore: plant and flesh eating animal e.g. hedge hog, field mouse.
Decomposer: detritus feeder e.g. earthworm, most bacteria and fungi.
Saprophyte: bacterium or fungus that feeds on detritus.
Feeding Relationships
Food Chain: a list of species, each being food for the next species in the list, i.e.
Grass > Rabbit > Fox
Bramble > Aphid > Ladybird > Sparrow > Hawk
Trophic Level: the position of a species in a food chain.
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Bramble: first trophic level or primary producer.
Aphid: second trophic level or primary consumer.
Ladybird: third trophic level or secondary consumer.
Sparrow: fourth trophic level or tertiary consumer.
Hawk: fifth trophic lever or quaternary consumer.
Short Food Chains
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Inefficiency of energy transfer to the next trophic level.
The energy needs of each organism is about 90% of its food intake.
Almost 90% of an organism’s food is used in respiration.
Food Web
A food web is a flow chart showing the feeding connections in a community.
Textbook Diagram: food web diagram.
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A food web is made by linking food chains.
The links are food sources used by two or more species.
All species in a community are connected through the food web.
A change in any one species causes changes in all populations.
Pyramid of Numbers
A Pyramid of Numbers is a bar chart showing the number of individuals at each trophic level of a food
chain.
Textbook Diagram: normal and inverted pyramids of numbers.
The number at each trophic level is influence by:
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Energy needs of an individual - the lower the need the great the population.
Mass of an individual - the greater the mass the greater its energy needs.
Energy transfer - only about 10% is transferred to the next level.
Other food sources - the species may be a member of other food chains.
Energy Flow
Textbook Diagram: flow char for energy flow.
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About 1% of sunlight energy used for photosynthesis by primary producers.
Each trophic level 90% of the food is used for respiration and lost as heat.
Only about 10% of the food energy is transferred to the next trophic level.
Detritus (dead organic matter) is a very important energy source.
Ecological Cycles
Nutrient Cycling
Textbook Diagram: mineral cycling flow chart.
Carbon Cycle
Textbook Diagram: carbon cycle flow chart.
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Carbon dioxide is the source of carbon and oxygen for organic molecules.
Water is the source of hydrogen for biomolecules.
Plants get the other elements as soluble salts from the abiotic environment.
Plants are the direct or indirect source of nutrients for consumers.
Consumers ‘steal’ the materials they need, as food, from other organisms.
Decomposers return the inorganic nutrients to the abiotic environment.
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Carbon is the most important element in biomolecules as it forms their skeletal framework.
Nitrogen Cycle
Textbook Diagram: nitrogen cycle flow chart.
Bacteria in the Nitrogen Cycle - how they benefit from their roles in the nitrogen cycle:
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Nitrogen Fixing Bacteria: usuable form of nitrogen for biomolecule formation.
Saprophytic Bacteria: receive a supply of materials for energy, growth and reproduction.
Nitrifying Bacteria: produce ATP by the nitrification process.
Denitrifying Bacteria: nitrites and nitrates are their oxygen source for ATP formation.
Biotic Factors
Competition
Competition is the rivalry between individuals of the same or different species for the same resources.
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Plant Example: grass and daisies compete for light, space, water.
Animal Example: fox and hedgehog compete for food e.g. earthworms.
Competitive Adaptations
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Yellow petals of buttercup flower: to win the battle for insect pollinators.
Antibiotics secreted by soil bacterial to inhibit their competitors for nutrients.
Ecological Benefit of Competition
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Controls and limits the size of the competitive species.
Maintains a species at a sustainable level.
Competition is a major factor in the evolution.
Important factor in maintaining the ‘balance of nature’ in the community.
Predation
Predation is the hunting and killing of one animal by another for food.
Examples: fox killing rabbits; ladybird killing aphids.
Ecological Benefit of Predation
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Maintains the prey species at a sustainable level.
Predation is a major factor in the evolution of the prey species.
Predator Adaptations, e.g., fox.
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Reddish fur: camouflage to avoid detection by rabbits.
Long canine teeth: to kill the prey and tear flesh from it when feeding.
Great speed: to outrun the prey to capture it.
Prey Adaptations, e.g., rabbit.
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Rests underground: predator avoidance.
Long ears: good hearing to detect the predator.
White tail: conspicuous warning signal to other rabbits.
Textbook Diagram: Predator-Prey Graph - Know how to interpret this graph.
Symbiosis
Symbiosis is the relationship between individuals of two or mores species living together.
Commensalism: symbiosis where one species gains benefit and the other species does not gain but is
not at any serious disadvantage. Example: lichens and trees - the lichens gain a place to grow.
Parasitism: symbiosis where one species feeds off and harms the other. Example: lice on hawks.
Mutualism: symbiosis where all species gain. Example: lichens - the fungus gains food from the algae
and the algae gain shelter, water plus mineral nutrients from the fungus.
Niche
A species niche is everything about how it lives and fits into the community.
Each species in a community has a unique niche.
Human Population
Food supply and disease are the major factors affecting human population.
Great prosperity is a major factor influencing the population of developed countries.
Textbook Diagram: Human Population Graph
The greater the food supply the greater the potential for population growth.
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Famine reduces the population - death and/or migration.
Famine is often linked to war - war zones have reduced agricultural activity.
Prosperity leads to population reduction due to a decline in the birth rate.
Convenient, effective and easily available contraception reduces the birth rate.
Disease, especially among infants, often results in a high death rate.
Modern medical practice has massively reduced the death rate from disease.
Modern medicine and absence of contraception has led to hugh population increase in many
developing nations.
Human Impact on an Ecosystem
Conservation
Conservation is positive care management of the environment to maintain biodiversity.
Involved Activities:
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preservation of ecosystems
restoration of spoilt habitats
balanced use of resources
the safeguarding endangered species
Example of Conservation Practice (only one example required)
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Set-aside in Agriculture
Farmland - a commercially managed habitat
Reduced species diversity, low population of native species
Set-aside - agricultural activity suspended in part of the farm
‘Return to nature’ and/or reintroduction of ‘lost’ species
Natural community re-established
Pollution
Pollution is any human activity that contaminates any part of the biosphere with substances that
degrade or harm the natural community.
Pollution also threatens
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human health
food production
supply of natural raw materials
restricts recreational activities
future generations are denied their right to a wholesome planet
Pollutant: a substance made during human activity in a quantity that harms the natural environment.
Sulphur Dioxide - an example of a pollutant (only one required)
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Main Source: fossil fuel burning.
Converted to sulphuric acid in the atmosphere.
Pollution of land and water habitats by ‘acid rain’.
Increased acidity of soil and water - plant and animal life directly inhibited.
Soil Problems - less fertile.
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Toxic metal levels increased.
Reduced mineral recycling due to decline in the populations of bacteria and fungi.
Aquatic Habitat Problems
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Acidification kills algae and bacteria.
Insect and fish life decline.
Ultimately - lifeless lakes.
Terrestrial Plant Problems
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Damages cell membranes and destroys chlorophyll.
Weakens plant’s immune system - greater disease damage.
Human Health Problems
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Lung and breathing trouble.
Metal contaminated drinking water can cause nervous system difficulties.
Building Damage
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Stonework, mortar and metalwork attacked.
Sulphur Dioxide Control
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Burn natural gas instead of coal, oil or peat.
Remove sulphur dioxide before the waste gases are released.
Greater use of renewable energy sources and nuclear power.
Less use of the car - greater use of public transport.
Spread lime - reduces soil and water acidity.
Fossil Fuel Burning - an example of one human polluting activity. <SSH> (only one required)
Acid Rain
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sulphur dioxide causes two thirds of the problem
nitrogen oxides causes the remainder of the problem
Carbon Dioxide - suspect in ‘Global Warming’ (enhanced Greenhouse Effect)
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Carbon dioxide levels have risen by almost 30% since Industrial Revolution.
Carbon dioxide is a ‘greenhouse gas’.
Atmospheric temperature has been increasing.
Is carbon dioxide a major factor in ‘global warming’.
Suspected effects of ‘global warming’: sea level rise, climate change, increased
desertification, less agricultural land, plant and animal distribution changes.
Smoke: huge mass of tiny carbon particles.
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Reduce photosynthesis - less light and blocked stomata.
Human health - lung damage.
Role of Micro-organisms in Pollution Control
Organic Waste (i.e. human sewage and farm slurry.)
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Organic waste is food and nutrient source for bacteria and fungi.
Increased use of special ‘fermenters’ for household, district and city waste.
The natural gas produced can be used as an energy source.
Waste reduced to by 98% i.e. 2% of original mass.
Oil Spillage: bacterial decomposition of oil, speed up by inoculating the oil.
Bioremediation: bacteria and fungi can be used to decontaminate soil and groundwater of pesticides,
metals and even radioactive materials.
Waste Management
Major Problems
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Large volume: domestic (2 mt), agricultural (22 mt), industrial (6 mt) in Ireland. {mt =
million tonnes}
Disposal: landfill, recycle, destroy or convert to other uses.
Landfill Difficulties
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Local groundwater polluted.
Current sites almost full – strong local protest against new sites.
Incineration Difficulties
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Atmospheric pollution - local and regional.
Strong local protest against placing an incinerator in their area.
Possible pollution of ground water.
Waste Minimisation
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Much better than waste disposal.
Packaging makes up 50% of domestic waste and is easy to reduce.
New uses for materials previously dealt with as waste e.g. much slurry now use as organic
fertiliser; fish waste used as poultry or pig feed; forestry waste now converted to sawdust for
processed wood.
Recycle: multiple uses - glass bottles, metal cans, and paper.
Role of Micro-organisms in Waste Management
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Breakdown of domestic and agricultural organic waste by bacteria and fungi.
Purposely designed treatment tanks are used for aerobic and anaerobic decay.
Kitchen organic waste can be broken down in a ‘compost bin’ for garden fertiliser.
Ecological Fieldwork: Principles and Practices
Grassland Habitat
Description of Habitat: General Map and/or Photographs taken at different seasons.
Climate: Cold Temperate Oceanic
Grassland Diversity of Living Organisms
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Kingdom Monera: bacteria - saprophytic, nitrogen fixing, nitrifying bacteria.
Kingdom Fungi: yeast of leaves, common field mushroom.
Kingdom Protoctista: Amoeba in damp soil, Pleurococcus on rock and tree bark.
Plant Kingdom: grass, daisy, buttercup, dandelion, clover, bramble, oak, ash.
Animal Kingdom: rabbit, fox, aphid, earthworm, sparrow, hawk, mouse, badger.
Microhabitats within the Grassland Habitat
Soil, ditch, oak aerial system, hedgerow, stone wall, oak root system.
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A study to discover which species are present in the habitat.
The study will also include absence of expected species.
The unexpected presence or absence of species can indicate unusual environmental
conditions.
Identification keys, charts, books can be used to name species.
Quantitative Survey
A study to measure the distribution, population, frequency or cover of a species.
Display of Results
Graphs, histograms, bar charts, pie chart, flow charts and maps can give a much clearer report of the
survey results than a long piece of prose.
Local Ecological Issues Related to the Grassland Habitat
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Bird and rabbit kills by local domestic cats.
Exotic garden plants colonising the habitat.
Fragmented distribution of daisies and buttercups due to recreational use.
Increased sparrow population due to local bird feeders.
Mandatory Activities
Identification Using a Key
The field key below is a dichotomous key.
It is a sequence of pairs of statements only one of a pair applies to the organism you to identify.
1
(a) Animal with backbone 2
(b) Animal without backbone 3
2.
(a) Covering of feathers 4
(b) Covering of hair 5
3.
(a) Tough hard outer body 6
(b) Soft body 7
4.
(a) Red feathers covering upper chest - Robin
(b) Large black and white - Magpie
5.
(a) Dog-like, long bushy tail - Fox
(b) Long ears, short white tail - Rabbit.
6.
(a) Three pairs of legs - Insect
(b) Four pairs of legs - Spider
7.
(a) Segmented body - Earthworm
(b) Unsegmented - Slug
Identification Steps for Spider: 1(b), 3 (a), 6 (b).
Description of Earthworm from Key: segmented body, soft, no backbone.
Conduct a Quantitative Survey of Plants, e.g., distribution of daisies
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Method: Line Transect (x3)
Set a measuring tape straight across the habitat in the direction of change in an influential
environmental factor e.g. soil water, pH, and nitrogen content.
On a map of the habitat mark the trace of tape - this is a line transect.
Walk beside the line and indicate, on the map, the position of each daisy plant touched by
the line.
Repeat the process twice more from other start positions.
Combine the results to establish the daisy distribution.
Relate the distribution to the variation of the environmental factors.
A map is an appropriate mode for the display of the results.
Conduct a Quantitative Survey of Animals, e.g., fieldmouse population
Day 1
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Capture field mice using small mammal traps.
Record the number of captured mice e.g. 20.
Mark each with a dab of red paint on the belly surface.
Release each at their capture site.
Allow time for the mice to readjust to normal conditions.
Day 2
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Capture field mice as before.
Record the number captured e.g. 18.
Record the number of recaptures (marked mice) e.g. 6.
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Return the mice to the habitat at their capture site.
Calculation:
Population
=
Day 1 Captures x Day 2 Captures
Number of Recaptures
= 20 x 18
6
= 60 mice
Change in population over a year is best displayed as a graph.
Determining the Frequency of a Plant Species
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Method: many random quadrats e.g. 100.
Randomly pick quadrat sites within the habitat.
At each quadrat record the plant species present.
For each species record the number of quadrats is was found in.
This number is its frequency if a hundred quadrats were used.
Frequency is the percentage occurrence of a species with a large sample of randomly chosen
quadrats.
Suitable Quadrat Size: 1/4 m2 (0.25 m2 ).
Frequency is displayed clearly as a bar chart.
Determining the Percentage Cover of Sedentary Species
Textbook Diagram: pin-frame
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Method: pin-frame.
Set out a straight transect line across the habitat.
Place the pin-frame beside the line at the start.
Push down each pin, to the ground, and record the species touched.
Move the frame to the next half-metre and repeat.
Record the total number of pins used.
For each species record the number of ‘hits’.
Calculation:
Percentage Cover = Number of ‘Hits’ x 100
Total Number of Pins
Percentage cover is the proportion of ground screened or occupied by a species.
Percentage cover is distinctly presented as a pie chart or histogram.
Investigation of Abiotic Factors (Three Mandatory Activities)
Soil pH
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Air-dry the soil - leave exposed to air until constant mass.
Sprinkle a small pinch of soil onto a white plate.
Add universal indicator solution until soil is quite wet.
Thoroughly mix the soil and the universal indicator.
Press the mixture so some indicator oozes out.
Match the indicator colour to a colour on the pH chart.
The number on the matching colour is the soil pH.
Cowslip and rock rose prefer basic soils.
Heather and bilberry prefer acidic soils.
Percentage Soil Water
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Using a scales find the mass of an evaporating dish, e.g. 15g.
Find the mass of the dish plus fresh soil, e.g. 55g.
Subtract to calculate the mass of the fresh soil, e.g. 40g.
Dry the soil in an oven at 1008C until constant mass.
Find the mass of the dish plus the dry soil, e.g. 45g.
Mass of Soil Water = (ii) - (v) = 10g.
Calculation:
Percentage Soil Water = Mass of Soil Water x 100
Mass of Fresh Soil
= 10g x 100
40g
= 25%
The common rush prefers soil with a high percentage of water.
Daisies prefer soil of medium water content.
Adaptations of Organisms to their Environment
An adaptation is a feature that suits the organism to its environment. Adaptations are solutions to a
problem.
Examples of Adaptations (see also competitive, predator and prey adaptations.)
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Needle-like mouth parts of aphids tap food from the phloem of the plant.
Ladybird warning colouration: releases toxic fluids to deter predators.
Grass shoot tips are at or below ground: adaptation to survive grazing.
Field mice are nocturnal: predator avoidance.
Collection Methods in Ecological Studies (Mandatory Activity)
Textbook Diagrams of the following:
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Small Mammal Trap
Pitfall Trap
Cryptozoic Trap
Pooter
Net: sweep net, insect net, plankton net or fish net.
Tullgren Funnel
Direct search for a particular species is a common practice.
Errors During Fieldwork
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Bias: purposely choosing sample sites to get ‘good results’ or avoid work.
Too Few Sample Sites: may not give accurate representative results.
Surveyor Variation: students vary in ability, commitment and interest.
Equipment Quality: measurement and trapping success will be affected.
Changing Nature: results may depend on the time of day, season or year.
Chance: cannot survey every square centimetre so even with many sites some species may
be missed.
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Improper Trapping Techniques: all evasive species may not be captured and/or insufficient
numbers captured in follow up surveying.