Ecology C H A P T E R 7 Stimulus questions 1 Why don’t plants grow on the deep ocean floor? 2 What tree has its roots above the ground? 3 How do sharks clean their teeth? 4 What do spiders and mushrooms have in common? 5 Where can you find ‘living rocks’? Outcomes Biological science 4.1 Identify relationships between living things which help them survive in their habitat. 5.2 Describe interactions between living things and between living things and their non-living surroundings.
Transcript
EcologyC H A P T E R 7
Stimulus questions1 Why don’t plants grow on the deep ocean floor?2 What tree has its roots above the ground?3 How do sharks clean their teeth?4 What do spiders and mushrooms have in common?5 Where can you find ‘living rocks’?
OutcomesBiological science
4.1Identify relationships between living things whichhelp them survive in their habitat.
5.2Describe interactions between living things andbetween living things and their non-livingsurroundings.
When we talk about an ecosystem, we arereferring to the living organisms that inhabita specific area, how they interact with eachother, and the effects of the non-livingenvironment around them.The term living organisms includes all of the plantsand animals in the region being considered. Together,they comprise the community of that ecosystem.
The term non-living environment includes all ofthe physical factors such as rainfall, the amount of lightthat is available, the temperature, the rocks and soil (ina land or terrestrial environment), and water (in anaquatic environment).
As you can see, an ecosystem can be quite acomplicated thing!
BiospheresnThe study of ecology involves the study of an organism’shome. Just as you have an address, so too we can give anaddress to the organisms that live in a specific area.
The term biosphere is the broadest category in theaddress. It refers to that part of the earth (including its
161 Chapter 7 Ecology
atmosphere) in which livingorganisms can be found. Theearth biosphere is further dividedinto biogeographical regions.For example, Australia andNorth America arebiogeographical regions. Eachregion has its own unique plantand animal life. These interactwith each other, and depend onthe unique physical conditionsthat are present there.
BiomesnThe biome is the third level ofan organism’s address, andrefers to areas that have similar climaticconditions. This means that they have similar soil types,rainfall, temperature and so on. Examples of differentbiomes include grassland biomes; desert biomes; arcticbiomes; tropical and subtropical biomes. Scientists haveobserved that organisms living in the same biome, eventhough they may be in different biogeographicalregions, have similar features. For example, the SimpsonDesert is a desert biome in the Australianbiogeographical region. The plants and animals that arefound in this area show characteristics similar to thosefound in desert biomes in other parts of the world.
Unit 7.1 Ecosystems
Fig 7.1.1 This spotted pardalote is shown here at its nesthole inAustralian woodland.
Biosphere 2Biosphere 2 is a human-madestructure covering 3.15 acresnear Oracle, Arizona in theUnited States of America.Four men and four womenlived within the 7 millioncubic feet structure, alongwith more than 3800 otherplant and animal species, for 2 years in order to studyplant–animal–maninteractions. The outcome?Failure! It appears that thereis a lot more to an ecosystemthan was ever imagined.
Sciencesnippet
Migration
Some animals can move from one biome to another.
Salmon begin their lives in a freshwater biome and then
move to an ocean saltwater biome to mature. When they
are ready to reproduce, they migrate back to their original
freshwater home to lay their eggs. Once the eggs are laid,
the adult salmon die, their bodies providing food for the
fingerlings (baby salmon).
Science snippet
Fig 7.1.4 A clay pan habitat in the Simpson Desert. Believe it or not,this dry, lifeless-looking place is actually home to a number
of different living things.
HabitatsnWithin each biome, we find different habitats, thefourth level of an organism’s address. This term definesan even more specific area. In a desert biome thehabitats may include the individual sand dunes; the claypans between them; or a tussock of grass or scraggly treegrowing on them. A tropical biome will have vastlydifferent habitats when compared to a desert biome.These include the moist, protected areas at ground leveland the very top of the leaf canopy—and everything inbetween!
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MicrohabitatsnYou may think that we can’t get any more specific thansaying an organism lives on the ground in a tropicalrainforest or on a sandy dune in the desert. Think again!In every habitat there are areas where conditions varyfrom the rest of the habitat. In a tropical rainforest,some organisms may live between the roots of the trees, others under the bark. On a desert sand dune, a few centimetres below the surface beneath a clump of spinifex, you may find a kowari sleeping quite happilyin its own microhabitat! As you can see, the
7.1.3 Herds of camels can be found grazing on the tough grasses of the Simpson Desert, able to thrive in the Australian desert
biome which is similar in climate to the desert biome of their home countries.
Fig 7.1.2 World distribution map of the locations of different biomes
Cold temperate coniferous forests
High mountains
Equatorial and tropical rainforests
Tropical monsoon forests
Mediterranean shrub woodlands
Temperate forests (evergreen and deciduous)
Tropical savanna grasslands
Temperate grasslands
Deserts and semi-desert
Tundra
microhabitat is the most specific part of anorganism’s ‘address’.
Look at the kowari in Fig 7.1.5. This tinymarsupial lives in central Australia (itsbiogeographical region) in the stony deserts (itsbiome) that are foundthere. Its habitat is thedunes and clay pans,where at night the kowarihunts for food. Duringthe heat of the day, thekowari returns to itsburrow a few centimetresbelow the surface. This isits microhabitat. Thecommunity of organismsthat are a part of thekowari’s ecosysteminclude the plants thatprovide shelter, nestingmaterials and food for thesmall birds, marsupial mice and lizards that it eats, aswell as for itself. The non-living environmentincludes the soil type of the dunes, therainfall and the temperature of the desert.Everything in the ecosystem is connectedin some way—like the threads of a wovenpicture tapestry.
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U N I T 7 . 1
A differentworld
The use of cane toads to
control the sugar cane
beetle has proved
unsuccessful. Why? Because
cane toads live on the
ground, and the beetles live
at the top of the cane plant!
Living in a different
microhabitat can be like
living in a different world.
Fig 7.1.5 This small, alert and tenacious little marsupial is found incentral Australia and is known as the kowari.
Prac 1p. 164
1 How would you describe the term ‘ecosystem’?2 Define the term ‘a community of organisms’.3 What is your address? Use the following list as a guide. The
first level is done for you.
Biosphere The Earth
Biogeographical region (your country)
Biome (your city)
Habitat (your street)
Microhabitat (your house or apartment number)
4 Are the following living (L) or non-living (NL)?a A seedb Dried flowersc The bark on a treed A tumbleweede The hair in a hairbrush
5 List some of the differences between plants and animals.6 Copy the true statements in the following list into your
workbook. Rewrite all the incorrect statements so that they aretrue:a ‘Ecosystem’ refers to the plants that live in a specific area.b The plants and animals in each biogeographical region are
unique.c Animals that live in a grassland biome in different
biogeographical regions are unlikely to show anysimilarities.
d The island of Tasmania is considered a microhabitat.7 Place in order from smallest (most specific) to largest (least
8 Give an example for each of the above.9 List five biogeographical regions in our biosphere.
10 Name four different types of biomes.11 Replace the word or words in italics in the following statements
to make the statement correct.a The term ‘biosphere’ refers to that part of the earth (except
its atmosphere) in which living organisms can be found.b The term ‘biome’ refers to areas that have different climatic
conditions.c The term ‘habitat’ is used to describe a less specific area
than the term ‘biome’.d An example of a desert microhabitat would be the Simpson
Desert.
U n i t 7 . 1 Questions
Sciencesnippet
12 Year 8 students at two high schools, Class A in AliceSprings and Class M in Melbourne, were asked torecord the amount of rainfall that fell during the period 1 May to 1 October. Class A recorded less than 90 mmof rain, and Class M recorded 300 mm of rain. In lightof this information, do you think the vegetation of AliceSprings and Melbourne would be the same? Suggesthow they might be different.
13 Not all water environments are the same. Consider thesaltwater oceans, freshwater rivers or lakes, dams oreven the family fish tank. List three factors that might bedifferent, depending on the particular water environmentyou are considering.
14 Draw a line to connect the appropriate terms in eachlist.
Carnarvon Gorge, Queensland biosphere
The upstream side of a river rock habitat
Earth temperate biome
Carnarvon river microhabitat
15 Why do you think that organisms living in the same typeof biome might have similar characteristics?
16 How do you think animals such as the kowari survivethe hot desert dust storms that often whip across theland?
17 What are some of the characteristics (behavioural andphysical) you might find in organisms that live in adesert biome?
18 When adult salmon have laid their eggs, they die. Thisis essential if the ‘fingerlings’ are to survive. Suggest areason why.
19 People who keep fish must be careful to keep the waterin their fish tank fresh. To do this, they replace about70% of the water every few weeks. Why do they needto do this, and why don’t they replace all of the water atthe same time?
1 Research the Carnarvon Gorge, Queensland. On a mapof Australia, indicate where the gorge is located.What type of plants and animals live in the gorge?What feature of the gorge makes it possible for lichensand moss to exist there?
2 Research your own backyard or school ground.What plants and animals live there?What are their water requirements?What types of soil do they live in?How do the plants in your chosen area interact witheach other?How would you classify the area?
Unit 7.1 Prac 1Cut and paste
What to doCopy the following table into your notebook. Cut out each ofthe dotted outlines found in Fig 7.1.6 and paste them intothe appropriately labelled section. (Your teacher will provideyou with a photocopy of Fig 7.1.6 that you may cut up.)
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U n i t 7 . 1 Research/Extension
U n i t 7 . 1 Practicalactivity
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U N I T 7 . 1C R E A T I V E W R I T I N G
A day in the life of…Imagine you are kowari (or some other animalof your choice). Write a short story about youractivities over the last 24 hours. Include in yourstory a description of your home, what youhave eaten during this time and perhaps anadventure or two that you have had this day.
P R O J E C TThe mini-biome
Plan to make your own mini-biome in anaquarium. Model it after something thatinterests you, using the materials you wouldnormally find in that particular biome.
This is called a ‘closed system’. Suggest why.What problems do you think you might
encounter?Can a closed system accurately represent a
biome? Why?
Biosphere Biome
Biogeographical region Habitat
Microhabitat
Fig 7.1.6 WS 7.1
An organism’s environment can be definedas all of the living and non-living things thatsurround it, and can be categorised as eithera land environment or a water environment.An organism can live only in that environment forwhich it has the appropriate behavioural or physicalcharacteristics. These characteristics are calledadaptations.
Consider the echidna. This mammal has a stockybody that is covered, on the back and sides, with spines.Between the spines is a thick, coarse fur, the amountand colour of which depends on where the echidnalives. The colour of the spines also varies, and each onemay have several bands ofcolour, providing an effectivecamouflage from predators.Both the colour of the furand the presence and colourof spines are examples ofphysical adaptations—theyare things the echidna has nocontrol over.
On the other hand, whenan echidna is being attacked,it will roll into a tight balland, if the ground is softenough, it will dig itself intothe earth. This exposes itsspines, making the echidnaappear very unappetising tothe attacker! This is anexample of a behaviouraladaptation. Behaviouraladaptations can beinstinctive or can be learnt.
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Unit 7.2 Physical attributesof an ecosystem
Fig 7.2.1 The echidna—an Australian marsupial perfectly adapted to its environment
Fig 7.2.2 These bird beaks illustrate the physical adaptations of various bird species to thedifferent types of food they eat; in each case, these birds received the genetic materialthat coded for their beak shape and size from their parents.
seed-eatersfish-eater
scavengerhoneyeater
predator insect-eateromnivore
For example, on hot days people (and animals) like tosprawl out because it cools them down—in coolerweather they cuddle up. This is instinctive behaviour,something we do automatically. An example of learntbehaviour would be coming to the kitchen when wehear the table being set. Why? Because we have learntthat shortly after the table is set, dinner is served!
Effects of thennon-livingnenvironmentn
The non-living (or abiotic) factors that influence wherean organism can live include:1 the temperature
Biological processes (such as digestion, respiration,excretion and reproduction) take place under anoptimum temperature range. When living things gettoo hot or too cold, they do not function properly.
2 the humidity of the airThis refers to the amount of water vapour in the air.The amount of water lost from an organism into theair depends on the humidity of the air. If the air isvery humid (as in tropical biomes), the less waterplants and animals lose. On the other hand, desertbiomes have very littlehumidity, and plantsand animals that live inthese areas have specialfeatures to help themretain as much water aspossible.
3 the amount of lightavailableGreen plants rely onlight to provide themwith the energy theyneed to carry out photosynthesis. On land, light isreadily available. In a water environment, however,most of the light is reflected at the surface—withonly a small percentage (the green and blue coloursof the spectrum) penetrating to any depth. This is
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U N I T 7 . 2called the photic zone. For this reason, plants arenot found on the deep ocean floor.
4 oxygen availabilityOn land, the percentage of oxygen in the airdecreases with altitude. Water that flows quickly hasa higher oxygen content than water that is still.Under the soil, the amount of oxygen presentdepends on the size of soil particles and the spacesbetween them.
5 the acidity of the soil and waterPlants have a preferred soil acidity in which they liketo live, as do organisms that live in water. Wemeasure the acidity of something using a pH scale.
6 the salinity of the water surrounding, or available to,the organismSalinity is a measure of the ‘saltiness’ of the water.Freshwater and marine organisms show markeddifferences in the way their bodies function becauseof the salinity difference of their environments.
7 the mineral salts and trace elements availableWhere a plant lives is determined by what nutrientsare available in the soil.
8 wave and water currentsThe intertidal area is that area that lies betweenhigh and low tides. At low tide it is exposed to the
Sea lettuceSea lettuce is able to livemuch deeper than mostplants, because it is moreefficient at absorbing lightin the blue region of thespectrum than other plants.
Sciencesnippet
Prac 1p. 170
Prac 2p. 171
Fig 7.2.3 The albatross is a bird that lives close to the sea. Birds that live in this type of environment possess special salt glands.These
glands are situated on the head above their eyes.They are connected to thenostrils and remove any excess salt they consume.The salt runs out of thenostrils and down grooves in the side of the beak, finally dripping off the tip.
air, while at high tide itis completelysubmerged. Thoseorganisms that live inthis region must be ableto live in bothconditions.
The organisms thatlive in fast-flowingstreams require greatstrength as they battleagainst the force of thewater.
9 the wind and air currentsAreas that are heavilybuffeted by strong windscan be inhabited only byplants that have strong root systems.
Effects of the livingnenvironmentn
The living (or biotic) factors that influence where anorganism can live include all of the other plants andanimals that it comes into contact with directly, or isinfluenced by indirectly. Sometimes the relationship isbeneficial; at other times it is not.
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Consider the following factors:1 Competition
Often, animals living in the same area have the samefood or nesting requirements. This means that theamount of food or nesting materials available mustbe shared. Plants compete with each other fornutrients in the soil and for the light that is available.
2 DispersalThis refers to how an organism is scatteredthroughout anecosystem. Whileanimals canmove freely bythemselves,plants relyon suchthings as thewind, insectsor animals toaid them indispersion andtheir seeds areoften shaped tohelp them inthis process.
3 PredationThe term ‘predation’ refers to the act of one animalcatching and eating another. Every organism in theecosystem may either eat, or be eaten by, otherinhabitants in that particular area.
StromatolitesAt Shark Bay, in Western
Australia, ‘living rocks’
known as stromatolites
have been discovered.
Found just above the water
line, these rubber-like
algal mats look like rocks
as they dry and crack in
the sun, yet are actually
algae mixed with sand
sediments. They provide a
rich source of food for
other organisms that live
in that ecosystem.
Sciencesnippet
Fig 7.2.5 A bee collects pollen and transfers itfrom one plant to another, assistingin the reproductive process of thespecies
Fig 7.2.4 The effect of the wind on this pine tree can be clearly seen—this is the Jeffrey pine, found on Sentinel Dome in YosemiteNational Park in California, USA.
Mutual benefitSea anemones have been observed to ‘hitch’ a ride on the back ofhermit crabs. The hermit crab is camouflaged and protected by theanemone, and the anemone gains mobility! This is an example of arelationship that is mutually beneficial.The giant rafflesia is a parasitic plant that lives on otherclimbing plants in the forests of South-East Asia. For most of thetime, the rafflesia is hidden within its host. When it flowers,however, it produces a flower that is up to 7 kg in weight and emitsthe fragrance of rotting meat! This attracts the flies necessary forits pollination.
Science snippet
4 Human interventionHuman beings continue to be one of the mostpowerful and influential biotic factors on theecosystem. The effects humans have on theenvironment will be considered more fully in Unit7.4.
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U N I T 7 . 2
1 Define the term ‘environment’.2 Name three things that make up your environment.3 What is the difference between a behavioural
adaptation and a physical adaptation? Give anexample of each.
4 Replace the word or words in italics in the followingstatements to make the statement correct:a The non-living factors that influence where an
organism can live are called biotic factors.b The more saturated with water the air is, the less
humid it is.c On land, the percentage of oxygen in the air
increases with altitude.d Water that flows quickly has less oxygen than water
that is still.5 Animals tend to curl up when they are cold, and lie
sprawled out when they are hot. Is this a behavioural ora physical adaptation?
6 Camels have nostrils that can be closed. This is anadaptation to the sandy, wind-blown areas that theyinhabit. Is this a behavioural or a physical adaptation?Why?
7 The little penguin is a fish-eating bird. Draw the type ofbeak you would expect it to have. Is this a physical or abehavioural adaptation? Explain.
Fig 7.2.6 The predatory crocodile of Northern Australia can grow tolengths of up to 6 metres.
8 African finches and Australian finches have similarlyshaped beaks. Knowing that Australian finches eat avariety of seeds, what type of food would you expectAfrican finches to eat? What assumption might youmake about the habitats they live in?
9 Label the following statements either true (T) or false (F).a The colour of the background (for example, a rock
face) on which an organism lives is an example ofan abiotic factor.
b The amount of nutrients in the soil is an abioticfactor.
c The parasitic nematode Wuchereria bancrofti isresponsible for a condition known as elephantiasis inhumans. We can say that the human being is a partof the nematode’s biotic environment.
d Koalas and magpies living in the same tree arecompetitors.
10 Consider the following organisms. What are some of theabiotic factors that would influence them?a An orcab A red-back spiderc A mushroom on a forest floord Your family pet
11 For each of the above organisms, list some of the bioticfactors that would affect them.
12 List three of the abiotic factors that affect you.13 List three of the biotic factors that affect you.
Defence
Many animals have developed characteristics that enable them to
evade predators. The cane toad contains poison glands on its
shoulders, a physiological adaptation passed on by the parents.
The toad has caused the death of innumerable numbers of native
snakes and goannas, and has had no effect on the beetle it was
brought in to control!
Science snippet
U n i t 7 . 2 Questions
c the sea lettuce Ulva taeniata is particularly efficientin absorbing blue light
3 Research the habits of a family member (you may like toinclude the family pet) for 1 week. Make a record of tenhabits they have, and then state whether these areinstinctive or learnt.
Unit 7.2 Prac 1The effect of an abiotic factoron plant growth
The aim is to determine the effect of light availability onplant growth.
You will need6 individually potted seedlings—these must be of the samespecies, at the same stage of development, 2 covers—oneshould be translucent (allowing a small percentage of lightthrough), the other should be completely opaque (allowingno light through)
What to do1 Set aside two of the seedlings as control plants. Place
these in a sunlit position.2 Place two of the seedlings under the translucent cover.
Place the last two seedlings under the opaque cover.3 Monitor the plants for at least one week. During this
time, each seedling should be watered at the same timewith a specific amount of water. (Be careful not to over-water the plants.)
4 Record your findings at the end of the specified timeperiod.
Questions1 What was the point of using more seedlings than
required?2 Why was it important that the seedlings should be of the
same species and at the same stage of development?3 We refer to the two seedlings that were set aside and
given sunlight as the ‘control’ seedlings. Do you thinkthis is an appropriate name?What is the purpose of the control plants?
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14 Elephants have very large, thin ears. Suggest an abioticfactor that this may be an adaptation to. Explain youranswer.
15 Rivers drain into the sea. Why is it that fish living in thesea cannot be found in the rivers?
16 Suggest why marine mammals and marine fish havemany similar characteristics. Name some of the abioticfactors that affect both of them.
17 Farmers often grow legume crops, such as peas orclover, alternatively with other crops. Suggest why.
18 Both desert cacti and alpine pine trees have long,needle-shaped leaves. This is an adaptation to limitedwater availability. Considering the high snowfall ofmany alpine regions, why should pine trees exhibit sucha characteristic?
19 The ‘tree line’ is an imaginary line at a certain altitudeon a mountain beyond which no trees are found.Suggest a reason why the trees won’t grow beyond thispoint.
20 Mangroves live in intertidal areas (that is, those areasthat are exposed to the air at low tide, but are coveredin water at high tide.) What type of abiotic factors mightthey have to contend with during the course of a day?
1 Research the life cycle of a frog. What are the bioticand abiotic factors that influence the water phase of thelife cycle? How do these factors change when the frogmoves onto a land environment? What characteristics doadult frogs display that enable them to move to theirnew environment? Is the adult frog able to leave itswatery environment completely? Why or why not?
2 Light is a mixture of the colours red, orange, yellow,green, blue and violet in certain proportions. When lightenters water, each of these colours is refracted (bent) atdifferent angles, with the result that the blue and violetcolours, which are not bent as much as the red light,reach down further into the water than the other colours.Research more fully how light behaves in water, andthen suggest why:a deep sea fish usually appear dull in colourb coral reef fish usually appear brightly coloured
U n i t 7 . 2 Research/Extension
U n i t 7 . 2 Practicalactivities
171 Chapter 7 Ecology
U N I T 7 . 24 Design an experiment that would test other abiotic
factors such as the soil type, humidity, water availabilityand temperature.
Unit 7.2 Prac 2Testing for soil acidity aroundthe schoolyard
The aim is to test the acidity of the soil at various locationsaround the schoolyard.
You will need3 or 4 test tubes, distilled water, 3 or 4 beakers, glassstirring rod, universal indicator, filter paper (for example,coffee filter paper)
What to do1 Collect a sample of soil (only a large test tube full is
required) from several different areas around theschoolyard. Label these sample 1, sample 2 and so on.You could collect your samples from:a under a pine or eucalypt treeb from the middle of the playing fieldc near a rubbish bind by the bicycle racks
2 Place your sample into a beaker (label your beakerssample 1, sample 2 and so on), and add approximately100 mL of distilled water.
3 Stir the sample for some time, until everything is wellmixed. Allow the sample to settle.
4 Separate the water from the soil using a filter paper.5 Test the acidity of the water using universal indicator
paper.You will learn more about pH in SCI 3.
6 Record the results you obtained in a table. For example:
Questions1 Why was distilled water used rather than tap water?2 In the above table, what was the pH of sample 1? Is this
acidic or basic?3 How do you account for the results you obtained from
your samples?
Sample number pH value
Sample 1 6
acid
1 2 3 4 5 6 7 8 9 10 11 12 13 14
neutralstronger weaker
alkaline
weaker stronger
pH
Fig 7.2.7 The pH scale
C R E A T I V E W R I T I N G
Comment on the statement ‘Australia shouldhave more National Parks’. Do you agree withthis statement, or do you think we have enoughNational Parks? What role do parks play inthe conservation of the ecosystem? Is thisimportant?
C L A S S D E B A T E
Bushwalkers think that keeping the environmentfree from human interference is essential. Landdevelopers say that it is important to utilise theland we have to provide homes andrecreational facilities for people to enjoy. Thosein the mining and timber industries insist thatthe land should be used to provide the rawmaterials to meet the needs of technologicalprogress. What is your opinion?
photosynthesis, and can be written as a simple chemicalequation:
carbon dioxide + water glucose + oxygen(in the presence of sunlight
and chlorophyll)Those organisms that produce their own food are
often referred to as producers or autotrophs. They areessential because they provide oxygen and food for all ofthe other organisms in the ecosystem.
The flow of nutrientsnthrough an ecosystemn
Not all organisms produce their own food. We refer tothese organisms as consumers or heterotrophs. Animalsthat eat plants are referred to as primary consumers orherbivores. An example of a herbivore is the kangaroo.Often, these animals provide food for other animals. Theanimals that eat the herbivores are called secondaryconsumers or carnivores. A dingo would be considered acarnivore. Those consumers that are able to eat bothplants and animals are referred to as omnivores. Humanbeings are examples of omnivores.
The interaction between producers, primaryconsumers and secondary consumers (and sometimestertiary consumers) is illustrated in Fig 7.3.2.
This nutritional sequence is referred to as a foodchain. It is called a ‘chain’ because each living organismin the chain is like a ‘link’, and each one depends on theorganism that comes before it. In general, food chainsrarely have more than six links (called trophic levels). In every ecological community we find that several foodchains are interrelated because the organisms that makeup those food chains have various food sources. Thisinteraction of food chains is known as a food web.
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All living things require energy. This energyis used by the organism for growth, repairand reproduction, and allows the organismto do the things necessary for survival. Whatis the source of this energy?The answer lies some 150 000 000 km from Earth—theSun. A swirling mass of gas, the hydrogen in its core isconstantly being converted into helium in a nuclearreaction. This results in the release of a great deal ofenergy, which takes the form of light, heat, gammaradiation, X-rays, microwaves and radio waves.
Plants, green algae and a number of micro-organismsare able to use light from the Sun to provide the energythey need for life. They do this by converting carbondioxide and water into food (a simple sugar calledglucose) and oxygen. This process is called
Unit 7.3 Food chainsand food webs:
interactions of life
Fig 7.3.1 Sunlight is absorbed by the chlorophyll (this is what makes theleaf look green) in the leaf, providing the energy required toconvert the carbon dioxide (taken in through the leaves) andthe water (taken in through the roots) into glucose and oxygen.
sunlight
oxygen gas(exits throughstomata pores)
leaf containsthe pigmentchlorophyll
water andnutrients(via roots)
sugar(to rest
of plant)
carbondioxide
(throughstomata
Fig 7.3.3 An example of a simple food chain—we draw the arrow so that it pointsin the direction in which the food is going. Unfortunately, the cat hasbecome an all too common predator of our wildlife.
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U N I T 7 . 3
Fig 7.3.2 The interaction between producers, primary consumers,secondary consumers and tertiary consumers.
Fig 7.3.4 An example of a food web; animals are able to survive adverse conditions if they have more than one source of food.
Sun green water plants
small fish,crustaceans
carnivorous fish
penguin
The flow of energynthrough an ecosystemn
In an ecosystem, energy moves in one direction only.During photosynthesis, the chemical compound calledglucose is produced inside the leaves of plants fromcarbon dioxide and water. The energy for this to occuris provided by the Sun’s light. Thus we can say that lightenergy from the Sun has been converted into chemicalenergy inside the plant. Plants use only a small amount(approximately 0.2%) of the Sun’s energy available tothem, and at each level of the food chain only about5%–20 % of the energy available is transferred to thenext level. For this reason, the number of plants in anyecosystem is greater than the number of herbivores andcarnivores that eat them.
Decomposers: the lastnlink in the food chainn
The term organic matter refers to all matter in thebiosphere that comes from living organisms andcontains the element carbon. Organic material is
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BiodiversityBiodiversity refers to the number of different speciespresent in a community. It has been observed thatcommunities with high biodiversity (many differentspecies of plants and animals living together) surviveenvironmental changes better than communities withlow biodiversity (few different species of plants andanimals living together). This is because if anythinghappens to destroy one organism in a food chain, theorganisms in the community can resort to another foodsource. This increases the stability of the entirecommunity, enabling it to survive changes in theenvironment more easily.
Consider the following example. If the herbivores ina community rely on one plant species for all of theirfood needs, what would happen if that particular plantspecies is affected by disease and dies out completely? Itwould mean that the herbivores would also die and, inturn, the carnivores that ate them. If, on the other hand,the herbivores have a variety of plants to choose from,they can probably survive the loss of one particularspecies. By removing the natural vegetation of an areaand replacing it with one specific type of plant (forexample, a wheat crop), humans have reduced thebiodiversity of many ecosystems, with the result thatsome species are now extinct.
Fig 7.3.6 At each level of the food chain, energy is lost. For this reason,in any ecosystem, the number of producers present is greater
than the number of consumers present.This is represented by a ‘foodpyramid’.
Fig 7.3.5 A field of wheat. When many species of plants are replaced by asingle species, as farmers do when they grow crops, thebiodiversity of the ecosystem is reduced, causing it to be lessstable.
seal
fish
plankton
smallcrustaceans
175 Chapter 7 Ecology
U N I T 7 . 3
recycled within the ecosystem due to the activity ofdecomposers. This group of organisms breaks down thedead bodies of plants andanimals (organic matter)and makes the nutrients theycontain available once morefor plants to use in theirgrowth. Decomposersinclude bacteria and fungi.They are, in effect, nature’srecyclers.
Relationships betweennorganismsn
No plant or animal living in a community lives inisolation. This interaction may be either by direct (as inthe case of predation) or indirect (as in the case ofcompetition for food) contact.
The different types of interaction include:1 mutualism (symbiosis)
In this situation, both organisms benefit by theirrelationship with each other. An example ofmutualism is the relationship between an alga and afungus to form a lichen. In this case, the fungustakes up nutrients produced by the alga, while thealga is protected from drying out by the fungus.
2 commensalismOne species benefits from the interaction while theother species is unaffected. Remora are tropical fish
that, with the aid of a sucker-like pad on the topof their heads, can attach themselves to faster-swimming fish such as sharks, allowing them tocover a larger area in their search for food. Thesharks don’t benefit from the remora’s presence,but neither are they harmed.3 amensalism
One species is harmed from the interactionwhile the other species is unaffected. Anexample of this is the formation of trails leftby cows and sheep as they walk to and from
Fig 7.3.7 Mushrooms—one type of decomposer
Fig 7.3.8 Dung beetles have now been introduced into public parks bymany urban councils in an effort to reduce the amount of dogfaeces there.
Fig 7.3.9 A mutualistic relationship—such relationships work well, evenwhen they’re underwater! Sea anemones hitch rides on thebacks of hermit crabs to get around better.
DetritusFragments of dead organic material
present in soil are referred to as
detritus. Those organisms that eat
(ingest) this material are called
detritivores. Both earthworms and dung
beetles are examples of detritivores.
Sciencesnippet
Fig 7.3.10 Elephantiasis is caused by the parasitic filaria worm Wuchereria bancrofti, a nematode of tropical countries.
Kangaroos eating spinifex grass is an exampleof this form of interaction.
c parasitismA parasite is an organism that lives in or onanother organism, called the host. In most cases,the parasitic organism does not kill its host,although it can cause small to severe problems.
Unless preventative measures are taken,family dogs and cats are susceptible to havingparasitic tapeworms in their gut.
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feeding areas. They areunaffected by the trail,but the plants they walkon are destroyed.
4 competitionSometimes, severalspecies want the sameresources found in aparticular habitat. Thiscan includecompetition for bothfood and nestingmaterials. Plantscompete with eachother for the nutrientsin the soil, water andlight.
Weeds in the garden often crowd out otherplants. They grow so quickly that other plants sufferand die.
5 exploitationIn this situation, one species benefits from theinteraction while the other isharmed. This type ofinteraction includes:a predation
One species kills theother for food. Thisis most commonlyobserved between acarnivore and itsprey. An example ofthis is dingoeshunting and killingwallabies.
b herbivoryHerbivores eat plantsand, although they donot usually kill theplants, they canseverely diminish theirsize.
Bubblenetting
Did you know that killer
whales employ the
unusual food-gathering
technique of ‘bubble
netting’? In this
situation, several whales
swim below a school of
fish and then ascend
spirally upwards around
the fish, exhaling air as
they go up. The air forms
columns of bubbles that
surround the fish and
keep them in a close-knit
group, making it easier
for the whales to feed.
This is an example of
cooperative hunting.
Sciencesnippet
ParasitoidsSome parasites do kill their host. These are calledparasitoids. An example of a parasitoid is thebraconid fly, which lays its eggs inside the cabbagewhite caterpillar. When the eggs hatch, the flygrubs eat the caterpillar from the inside out!
Sciencesnippet
Clean teethIt was previously thoughtthat sharks had to keepswimming in order tobreathe. Recently, however,scientists have observedsharks resting on theocean floor, with theirmouths open. The reason?They are having their teethcleaned by lots of little‘cleaner fish’. Now that’s atrusting relationship!
Sciencesnippet
WS 7.2
177 Chapter 7 Ecology
U N I T 7 . 3
1 Draw a line to match the words in the first column withthe organism in the second column:
a autotroph a human being
b heterotroph a rose bush
c omnivore a koala
2 ‘The Sun is the source of all life on Earth.’ Do you agreewith this statement? Why or why not?
3 Do you think the term ‘producer’ is an accuratedescription of a green plant?Explain your reasoning.
4 Complete the following statement:During photosynthesis, __________ energy from the Sunis converted into __________ energy within plants.
5 The energy from producers is converted into what formsof energy in consumers?
6 Copy the true statements in the following list into yourworkbook. Rewrite all the incorrect statements so thatthey are true:a All living things require energy.b The carbon dioxide used by autotrophs is obtained
through the soil.c Chlorophyll is the green pigment found in the leaves
of plants.d Humans are examples of omnivores.e The number of different plants in an ecosystem is
referred to as biodiversity.7 Below is a diagram of a simple food chain. Draw in the
arrows to indicate which organism is eaten by the other:Grass mouse snake owl
8 Label the producer and the primary, secondary andtertiary consumers in the food chain in question 7.
9 Draw an example of a simple food chain that you mightfind in your own backyard.
10 The recycling of organic material is the main function ofwhich organisms?
11 How do decomposers differ from detritivores?12 A scientist was determining the number of food chains
present in several different areas. In area A, he foundten different food chains. In area B, he found fiftydifferent food chains. In which area would you expect tofind the greatest biodiversity? Explain your reasoning.
13 Why do you think food chains rarely have more than sixlinks?
U n i t 7 . 3 Questions14 Consider the following relationships, and label them either P
for parasitism, M for mutualism or C for commensalism.a The tapeworm Echinococcum granulosus and its dog hostb The fungus that causes tinea on a human footc Honey possums feed on the pollen of a number of native
banksias, dispersing the pollen as they move from tree totree
15 How would you classify the relationship between a dog andthe fleas it carries around on its body?
16 How would cooperative hunting benefit a carnivore species?17 In the zoo environment, not all of the animals are fed the
same amount of food. Is this fair? Explain your reasoning.18 How is it possible that two organisms of the same species
might require different quantities of food?19 Many carnivores exhibit a range of behaviours that assist
them in catching their prey. Suggest why.
1 Many carnivorous animals employ unique prey catchingstrategies. The angler fish uses a ‘lure’ to entice its prey intostriking distance. Other organisms, such as the prayingmantis, are the same colour as their surroundings (they arecamouflaged). Some, such as the killer whale and the hyena,work in a cooperative group.Research one particular organism that uses a unique prey-catching strategy.
2 Dingoes thrive in many different biomes, including the wetand dry tropics of Queensland; the arid and semi-arid regionof Central Australia; the cool coastal mountainous region ofsouth-east Australia and the humid coastal mountains ofeastern Australia. In each different habitat, the dingoes’ foodchain is different. Research the different habitats the dingoesoccupy and the food chains they are a part of.
3 How is camouflage used as a survival tool?Research three organisms that use camouflage effectively.
4 Can bacteria that cause disease be classed as parasites?Research one disease caused by a bacterium that interestsyou. Include in your study:a the symptoms of the diseaseb the types of people that are susceptible to this diseasec treatments that are used to help people recover from this
disease
U n i t 7 . 3 Research/Extension
Fig 7.4.1 As human populations increase, areas for plant and animal habitationdecrease, and the demands on the environment to produce food andliving requirements increase.
For thousands of years, most people livedand worked in small villages. Populationswere small and the natural resourcesaround them were all they needed tosurvive. People used simple handmade toolsand lived in simple dwellings lit by firelight.Clothes were handmade, and food waseither hunted or gathered from the localsurroundings.In the mid 1700s, however, the Industrial Revolutionbegan, and by the mid 1850s many small villages hadbecome industrial towns. Machine-made goods were indemand, and ways to transport them quickly from placeto place were soon required. Human culture, and inturn the environment, had been changed forever.
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PollutionnA pollutant is anything that makes the environmentunfit or unhealthy for the organisms that live there.
Pollutants effect theatmosphere, the land andthe water and, while theymay arise from such naturalcauses as volcanoes, they aremore commonly the resultof human activity.
Air pollutionIndustry releases a constantstream of pollutants into theatmosphere (including sulfurdioxide, nitrogen dioxide,carbon monoxide, carbondioxide, hydrogen sulfide, dust and smoke) as do motorvehicles (hydrocarbons, lead, nitric oxide and carbonmonoxide). In the presence of sunlight, thesecompounds react to form a variety ofpollutants such as ozone and nitric acid, andorganic compounds such as formaldehyde.
Global warmingOne of the major issues of this century is globalwarming. While some of the Sun’s light that enters theEarth’s atmosphere is absorbed by the living and non-living things on the Earth, some of it is re-emitted backinto the atmosphere as heat. Before the IndustrialRevolution, much of this heat was lost into space, andwhat remained warmed the Earth to a comfortabletemperature suitable for life. Since then, however, due
Unit 7.4 Effects ofhuman civilisation on
the ecosystem
Prac 1p. 184
Shortenedlife span
The average life span of
a tree in a rural setting
is about 150 years. In an
average city setting, it
is only 32 years, while
in the middle of a large
city, it can be as little
as 13 years.
Sciencesnippet
1750
1800
1850
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2050
10002000
12 000 11 000 10 000
9000 8000 70006000500040003000
predictedrange
Popu
latio
n (m
illio
ns)
Year
Fig 7.4.2 Heat is trapped between the blanket of greenhouse gases (carbon dioxide, water vapour, methane, nitrous oxide and ozone) and the Earth’ssurface, causing a global increase in temperature.
to the burning of fossil fuels (for example, coal), therehas been a large increase in the amount of certain gasesin the atmosphere. These gases are collectively knownas greenhouse gases and include carbon dioxide,methane, nitrous oxide, ozone and water vapour. Thishas caused the formation of a thick ‘blanket’ of gassurrounding the Earth, trapping the heat inside. This iscalled the greenhouse effect. In the last 100 years, theatmospheric temperature has risen 0.6°C, causing thesea level to rise by several inches. If this trend continueswe may expect to see further increases inboth temperature and sea levels, with theresult that many coastal regions will beflooded, and some ecological niches andtheir inhabitants will disappear.
Water pollutionThe waterways and oceans of the world have becomepolluted from a variety of sources. These include:• sewage
Sewage contains contaminants such as soap,detergents and other cleaning agents from washingmachines, dishwashers and bathing facilities, as wellas human wastes from toilets.
179 Chapter 7 Ecology
U N I T 7 . 4• agricultural run-off
Fertilisers add large quantities ofnitrogen and phosphorus to theecosystem. These find their wayinto both run-off water andgroundwater, eventually ending upin the oceans.
• sediment pollutionClearing the land for housingdevelopments and farming causeslarge-scale erosion. Soil particlesare washed into the waterways andcause silting.
• inorganic chemicalsIndustry releases inorganiccompounds directly intowaterways, or into the soil where they are thenpicked up and carried by groundwater into thewaterways. Chemicals released into the atmosphereare absorbed by rain droplets and fall to Earth asacid rain.
• salinisationThe removal of trees in order to plant crops and theuse of irrigation to water those same crops hasresulted in a rise in groundwater level.
Prac 2p. 185
Turning upthe heat
The United Nations’scientific advisory panel,the IntergovernmentalPanel on ClimateChange, has forecast arise in globaltemperature of 0.8°C to3.5°C by the year 2100 ifno action is taken to cutdown on the productionof greenhouse gases.
Sciencesnippet
felling of trees which would ‘lock up’ carbon dioxide
radiated energy from belowenergy from Sun
some of the energy is reflected off atmosphere
heat trapped by carbon dioxide in atmosphere
power stations: source of extra carbon dioxide exhausts from motor
vehicles add to the carbon dioxide in atmosphere
heat radiated off sea
burning of fossil fuels (coal, oil, etc.) also adds excess carbon dioxide to atmosphere
heat radiated from land
heat
Fig 7.4.3 When poisonous gases and vehicle exhaust fumes combine in the atmosphere with oxygen and moisture, a deadly mixture is produced.Thesepoisons are carried back to the soil in the rain and snow (now referred to as ‘acid rain’), killing lakes and forests and the organisms that live there.
As the water table rises, it brings with it dissolvedsalts from the rock surfaces. This increases thesalinity of the groundwater, making it unusable bymany plant species.
Soil pollutionThe two major causes of soil pollution (more commonlyreferred to as soil degradation) are overgrazing anddeforestation. The term ‘overgrazing’ is used to describethe destruction of land caused by allowing moreanimals to graze in an area than the area can sustain.Deforestation refers to the large-scale removal of trees.In both cases, removal of plant life makes the soilvulnerable to the effects of wind and rain. Uncontrollederosion results, and the land is devastated. More than
65% of the Earth’s soil degradation isdue to these two factors alone.
Currently, about 10% of theEarth’s surface has been reduced toa desert (called desertification), anda further 25% has been placed atrisk, including a very largeproportion of the Australiancontinent.
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Introduced speciesnWhat do the pig, the rabbit, the European carp, theprickly pear and the tamarisk tree all have in common?They were all brought to Australia (either deliberately or
Fig 7.4.4 Trees act like giant straws, sucking the water out of the groundand releasing it back into the atmosphere through their leaves
(in a process called transpiration).This keeps the water under the ground(the groundwater) at a lower level. When the trees are removed, this levelrises, bringing with it dissolved salts from the surrounding rocks and soil.Sometimes this ‘salty’ water rises to the surface of the ground, making thegrowth of other plants impossible.
Bigger desertDid you know that in the
last 20 years the Sahara
Desert in Mali has
increased in size by more
than 650 square kilometres?
Sciencesnippet
noxious fumes and poisonous gas from vehicles, power generation and heavy industry released to atmospherepollutants fall as acidic
rain, killing forests
sulfur dioxide becomes sulfuric acid droplets in clouds
top of ground water (the ‘watertable’)
water vapour exits leaf via stomata (pores)
water vapour leaf
soil
ground water
non-porous rock
roots take in water
WS 7.3
by accident) by the early settlers and are now causinghuge problems for our native plants and animals.Introduced species are often referred to as exoticspecies.
Pigs, brought by thesailors on the First Fleet,were allowed to roam freelyfor food. Many of them ranoff, and great numbers ofwild pigs soon began toestablish themselvesthroughout much ofQueensland and NSW.These feral pigs dig up largeareas of land, damagingnative plants and destroyingthe habitats of many ground-nesting birds and nativemammals.
The European carp, first introduced into Victorianfish farms in the 1870s, escaped into our waterways andbegan to reproduce. By 1976 they had managed toinhabit creeks and rivers as far north as Queensland.
It is the carp’s feeding behaviour that has caused themost problems. Taking in a mouthful of the muddy riverbottom, they then spit it out, putting the dirt and thesmall organisms it contains into suspension in the water.The carp then catch and eat these tiny organisms.
This method of feeding causes great damage to water
181 Chapter 7 Ecology
U N I T 7 . 4plants, whose shallow root systems are made unstablebecause of the removal of the mud.
Endangered speciesSadly, much of Australia’s wonderfully unique wildlife isbecoming endangered. This term refers to those plantsand animals that are in danger of extinction unless stepsare actively taken to remove the factors threateningthem. Species that are now no longerliving on our planet are said to beextinct.
Factors that threaten ournative wildlife include:• predation by introduced
species (for example, foxes andcats)
• competition with introducedspecies (such as sheep andcattle)
• the destruction of their habitatsby human beingsAn example of an endangered
species is the northern hairy-nosedwombat. Today, this quietmarsupial is found only inapproximately 1500 hectares ofsandy countryside in the EppingForest National Park, centralQueensland. It has been estimatedthat there are probably fewer than100 left. Cattle-grazing and theclearing of land, together with theintroduction of species such as thedingo (introduced very early on inAustralia’s history by the Aboriginalpeople) and the rabbit, havedevastated their numbers. To makethe situation worse, the northernhairy-nosed wombat has only oneoffspring every year. The baby takes1 year to wean and 3 years to reachsexual maturity. As you can see, thereproduction rate of the northernhairy-nosed wombat is very low.
Fig 7.4.5 The native bilbies that once inhabited this area are no longerable to do so due to poor farm management.The overgrazing bycattle has rendered the land unusable.
ExtinctionsDue to the destruction oftheir habitat and theintroduction of predatorssuch as foxes and cats,two-thirds of the nativeanimals in centralAustralia are now extinct.
Sciencesnippet
Earlyintroductions
Did you know that the
early English settlers
introduced rabbits and
foxes so that they could
continue their tradition of
fox hunting?
Prickly pearThe prickly pear cactus is
now spreading at a rate of
about 0.5 million hectares
per year. How many house
blocks is this?
Cane toadmenace
Cane toads were
introduced by man to
Gordonville, Queensland,
in 1935. They are a major
threat to native wildlife
and are expected to reach
Kakadu National Park in
the very near future.
Paperdemand
In the 1980s, the quantity
of paper consumed by the
United States of America
almost doubled. The
reason? The introduction
of printers and
photocopiers in the
workplaces of America.
Sciencesnippets
WS 7.4
Fig 7.4.6 The greater bilby—a tenacious little omnivore that is no matchfor introduced species such as foxes and feral cats
To help this wombat species survive, a number ofdifferent strategies have been suggested. These include:• splitting the colony into several groups. This will
prevent the whole population from being destroyedif a fatal disease should threaten them.
• monitoring the population carefully. Scientists eitherwatch the animals directly, or use a variety ofdevices. These include satellite tracking andhelicopter spotting.
• assisting during births. It is hoped that this willprevent any unnecessary deaths during the birthingprocess.
• releasing the offspring into suitable and protectedhabitats, where introduced species have been
removed. Captive breedingprograms in zoos provide anothersource of wombats that willeventually, it is hoped, be placedback into the wild.
Other endangered marsupialsinclude the Leadbeater’s possum,the little pygmy-possum, themountain pygmy-possum andseveral species of wallaby andpotoroo. Unfortunately, both thebroad-faced potoroo (last sighted in1875) and the desert rat-kangaroo(last sighted in 1935) are alreadythought to be extinct.
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Marsupials are not the only species under threat.Many birds, such as the night parrot and the helmetedhoneyeater, and many sea mammals, such as the bluewhale and the southern right whale together withseveral species of dolphin, are also endangered.
Frogs are considered to be the community’s‘environmental indicators’. This is because they breathethrough their skin and are in close association with thewater that is available in the habitat. Any pollutantspresent in the habitat usually affect them first. Amongthose that are feared endangered (or even possiblyextinct) is the gastric-brooding frog, which was last seenin 1985. This small, dull-coloured amphibian was foundonly in the Blackall and Conondale ranges in south-eastQueensland. This frog was unusual in that afterfertilisation, which occurs in the water, the female atethe eggs, regurgitating them when they had fullydeveloped into young frogs.
The Easterbilby
In recent years, efforts havebeen made to increasepublic awareness of theplight of the greater bilbyand the lesser bilby (ofwhich only a few hundredare left) by releasingchocolates in the shape ofbilbies at Easter time.
Sciencesnippet
Ulcer cure?How was it that the young tadpoles of the gastric-brooding frog were
not digested by their mother’s gastric juices? Scientists were hoping
that, when they found the answer to this question, they could help
people suffering from ulcers. Unfortunately, this frog is now feared to
be extinct, and the answers to these questions may never be known.
Fig 7.4.7 The gastric-brooding frog—logging and gold prospecting
have almost destroyed this amphibian’s habitat.
Science snippet
ConservationnConservation involves keeping alive all of the plantsand animals that live together in a specific habitat. Thisusually involves keeping the habitat undisturbed andfree of human interaction.
In order to maintain the biodiversity of a particularhabitat, both short-term and long-term conservationactions are often required. For example, consider theimpact of an oil spill. Conservationists work hard in theshort term to remove the oil from any ocean-goingmammals, turtles and birds that may be affected. Stepsare taken to restrict the oil from spreading further, andskimmer booms are used to remove the oil from thesurface of the water. In the long term, conservationistsoften pursue legal action in an effort to change the laws
183 Chapter 7 Ecology
U N I T 7 . 4regarding the transportation of oil, in the hope thatfuture spills will be avoided.
When we work to conserve one species in anecosystem, we are helping to conserve all of the speciesin that ecosystem because all of them interact with eachother in one way or another.
Why conserve?Humans rely on the living organisms around them.Plants provide us with the oxygen we need, as well asbeing food for us to eat. They are also food for theanimals we eat. In addition to this, plants and fungiprovide the ingredients for many of the pharmaceuticaldrugs we use when we are sick. It is estimated that ofthe 500 000 to 750 000 different species of plants on theEarth, only 10% have been investigated for theirchemical components. Who knows what future curesare to be found in the plants (and animals) we are todaydestroying?
Fig 7.4.8 Oil spills cause a great deal of destruction to the naturalenvironment.
Virus killer
A chemical that destroys viruses in infected cells has been
extracted from the Australian black bean tree. Scientists hope that
at some time in the future this chemical will be readily available to
treat viral infections which are presently untreatable.
Toad medicine
As destructive as the cane toad is to our Australian environment, it
does have some redeeming features. Did you know that Chinese
medicine manufacturers have been using it for centuries to treat
cardiovascular diseases and cancer?
Science snippets
1 What do we mean by ‘the Industrial Revolution’?2 How would you define the term ‘pollution’?3 List three common air pollutants found in today’s
industrialised cities.4 In the presence of sunlight, some of these pollutants
become even more deadly. List three products of thecombination of air pollutants with sunlight.
5 The life span of trees in the country is greater than thelife span of the same species of tree in the city. Why doyou think this is so?
6 Which two elements are most predominant inagricultural fertilisers?
7 What are the two major causes of salinisation ofwaterways?
8 Explain why overgrazing and deforestation cause soildegradation.
U n i t 7 . 4 Questions
WS 7.5
9 Which of the introduced species do you think hasproven to be the most damaging and the hardest tocontrol? Explain your reasoning.
10 What is meant by ‘biodiversity’?11 Why do you think that the more diverse a community is,
the more resilient against change it is?12 What do you think ‘desertified’ means?13 How have the advances in human technology effected
the environment?14 List four ways that a small population of an endangered
species can be helped to survive.15 Describe the short-term and long-term measures that may
be taken to stop an oil spill from spreading.16 How would you define the difference between an
endangered species and an extinct species?17 Why are frogs considered to be ‘environmental
indicators’?18 Explain the term ‘conservation’. How does helping one
species in a community help the others?19 List three reasons why it is important for human beings
to conserve the plants and animals in their environment.20 How do you think the effects of global warming can be
reduced?
1 Research one animal and/or plant that is nowendangered. Include in your research:a what the term ‘endangered’ meansb what has caused this animal and/or plant to
become endangeredc how many are left in their natural environment
nowd what steps are being taken to increase the
numbers of this animal and/or plante what the expected outcome of this situation is
2 Research a habitat that is in danger. Choose from:a disappearing rainforestsb endangered coral reefsc increasing salinity on farmlandsd disappearing wetlands
3 What is a captive breeding program? Discuss theimportance of zoos and captive breeding programsin light of the current dilemma facing many species.
Unit 7.4 Prac 1Simulating smog
The aim is to make a situation that mimics pollution in ourcities.
You will needA large glass beaker, some aluminium foil, ice cubes, somepaper tapers, matches, thermometer
What to do1 Place half a cup of water in the beaker, swirl it around
to wet the sides and then tip it out.2 Drop a lighted taper into the base of the beaker. Cover
the open top with the aluminium foil and make anindentation. Place the ice cubes in the depression youhave made. Place the thermometer between the foil andthe glass beaker.
3 Record the temperature inside the beaker and state whathappens as the air temperature inside the beaker fallsdue to the layer of cold air immediately under the foil.When the smoke particles and the moisture in the air gettrapped together near the surface, they form smog. Thesmog cannot escape from the bowl, and as it cools itfalls back toward the base.
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smouldering paper taper at base
blocks of ice
cold air forms beneath foil
aluminium foil
smog forms inthis region
beaker
thermometer
Fig 7.4.9 Using a beaker to illustrate how smog forms in cities
U n i t 7 . 4 Research/Extension
U n i t 7 . 4 Practicalactivities
185 Chapter 7 Ecology
U N I T 7 . 4Questions1 Suggest why smog occurs more in those cities which have
rivers running through them.2 Why does more smog form in winter than in summer?3 What was the point of wetting the inside of the beaker first?4 Do you think this is an accurate re-creation of city smog and
a climate?
Unit 7.4 Prac 2Simulating global warming
The aim is to observe the effect of an invisible ‘blanket’ on heatescape from a system.
You will need2 small fruit juice cartons ( ‘poppers’), 2 thermometers, 1 pair ofscissors, 2 microscope slides, sticky tape
What to do1 Cut a square hole in the large flat side of each of the
poppers. The hole should be just smaller than the width oftwo microscope slides.
2 Place two microscope slides over the hole of one of thepoppers, and stick it into place using the sticky tape,effectively sealing it. Leave the hole in the second popperopen to the air. Place the thermometers through the strawholes on each of the poppers. Seal around them with stickytape to prevent heat escaping.
3 Allow about 5 minutes for the temperature inside thepoppers to stabilise. Record the temperature inside bothpoppers.
Place the poppers and the thermometers on a sunnywindow sill.
4 Record the temperature inside each of the poppers every5 minutes.
What conclusion can you make about the results youobtained?
Questions1 Did the temperature rise inside the popper that had the
microscope slides covering the hole? Why? Was thiswhat you expected to happen?
2 Is this a good illustration of what is happening to theEarth? Why or why not?
C L A S SD E B A T E
Separate the class into two groups:• Group A — those that think advances in
technology should be allowed to continue in anuncontrolled fashion, with human needs andwants being more important than the health ofthe environment.
• Group B — those that think more stringentcontrols should be put into place to protect theenvironment, to the extent where technologytakes a backseat role in deference to theenvironment.Students should have the opportunity to collect
articles (newspapers, periodicals, Internet sources)to support their views.
Separate both group A and group B into smaller‘subgroups’. Have the students within each of thesesubgroups discuss the obligations andresponsibilities (if any) that human beings have forthe environment, balanced by those they have tomeet the needs of humans beings. Have themembers of each subgroup decide on twoobservations they feel best support their views.Students should record these on paper, and sharethem with the rest of their main group (A or B). Students in both of the main groups shouldselect the most persuasive points from thosesubmitted. Write these on the board, and have anopen discussion on the validity of each point. It isprobable that no single conclusion can be made.
70
80
90
100°C
70
80
90
100°C
juice OrangeOrange
juice
Cut a hole the width of 2 microscope slides. Leave open to the air.
Cover with 2 microscope slides and stick into place.
straw hole
place thermometer in straw hole
popper A
popper B
Cut a hole the width of 2 microscope slides.
Fig 7.4.10 An illustration of global warming using two ‘poppers’
1 Look at the following address. Underline the word in thebracket that correctly describes that part of the address.
15 Ecology Street (biosphere, biome, habitat,microhabitat)
Melbourne (biogeographical region, biome,habitat)
Victoria (biosphere, biogeographical region,biome)
Australia (biosphere, biogeographical region,biome)
Earth (biosphere, biogeographical region,biome)
2 How would you define the term ‘abiotic factor’ and howdoes it differ from a ‘biotic factor’?
3 List three abiotic and three biotic factors that effect you.4 Is temperature a biotic factor or an abiotic factor?5 Look at Fig 7.1.2. What do you notice about those
biomes that lie along the equator? Would you expect tofind similar plant life in these areas? Explain yourreasoning.
6 What name is given to those animals that catch and eatother animals? What physical features might you expectto find in such animals?
7 The ghost orchid lives in the beech and oak woods ofEurope. It contains no chlorophyll and is a pale pink incolour. A fungus has been found growing on its roots. Ifthe fungus is removed, the orchid soon dies. What roledo you think the fungus might play? What type ofrelationship is this?
8 How does the Sun’s energy end up on your dinnerplate?
9 How does planting trees have an effect on theenvironment?
SCI2 186
10 Comment on the statement, ‘The more specialised thehabitat, the more vulnerable the species is to anychange’.
11 Plants on the forest floor have more chlorophyll in theirleaves than plants in a more open aspect. Suggest why.
12 Some people buy worms to add to their soil. What roledo worms play in the ecosystem?
13 The leaves of the water lily float on the surface of thewater. What advantage does the lily gain by keeping itsleaves above the water, rather than having themsubmerged?
14 Deepwater algae contain red pigments that absorb onlythe blue wavelengths of light. Why is this anadvantage?
15 The greater bilby lives in the desert area of CentralAustralia. It has an omnivorous diet (this means it eatsboth plant and animal matter). Do you think thisprovides the bilby with an ecological advantagecompared to other animals that have a more limiteddiet? Explain.
16 What does the term ‘pollutant’ mean? What commonpollutants can be found around the schoolyard?
17 Feral pigs dig up native plants over large areas of land.Affected areas soon show erosional damage, renderingthem unusable. Explain how this happens.
18 Explain the concept of biodiversity.19 Communities of high biodiversity are able to withstand
changes to the environment better than those of lowbiodiversity. Explain.
20 Why is it important that human beings try to maintainand conserve the environments they live in?
Chapter review questions
C R E A T I V E W R I T I N GImagine you are a lawyer who has been asked to prosecute acompany that has been caught in the act of releasingthousands of litres of poisonous waste into a local creek. Yourtask is to speak out on behalf of the environment and the futureof the creek. Discuss the effects of the dumping of this waste,and explain why the company should clean up the mess.
WS 7.6
Unit 7.1 Ecosystems
Word Clue
1 eco ___ ___ ___ ___ ___ ___ All the living organisms (plant and animal) that inhabit a specific area and how they interactwith each other and the environment.
2 ___ omm___ ___ ___ ___ y The plants and animals inhabiting a specific area.
3 ter___ ___ ___ ___rial The land environment.
4 a___ ___ ___tic The water environment.
5 b___osph___ ___ ___ That part of the Earth where living organisms are found.
6 b___om___ ___ Areas that have similar climatic conditions.
7 h ___ b ___ tat A specific area within a biome that has particular characteristics.
8 mic ___ ___ ha ___ i ___ ___ ___ A specific area within a habitat. The most specific part of an organism’s ‘address’.
Unit 7.2 Physical attributes of an ecosystem
Word Clue
1 en ___ ___ ron ___ ___ ___ ___ All of the living and non-living things that surround an organism.
2 adap ___ ___ tions The behavioural and physical characteristics of an organism that enable an organism to livein its environment.
3 ab ___ ___ ___ ___ c The non-living factors that influence where an organism can live.
4 p___ o ___ ic z ___ ne That area under the surface of the ocean where light can reach.
5 ___H A measure of how acidic something is.
6 b ___ ___ ___ ic The living factors that influence where an organism can live.
7 compet___ ___ ___ ___ n What occurs when plants and animals have to share the resources of the environmentbetween them.
8 disp ___ ___ sal The process of scattering something.
9 pred ___ ___ ion When one animal catches and eats another.
Unit 7.3 Food chains and food webs: interactions of life
Word Clue
1 gl___ ___ ___ ___ ___ A simple sugar.
2 phot___ ___ ___ ___ th ___ ___ ___ ___ The process where sunlight is used to convert carbon dioxide and water into glucose and oxygen.
3 p___ ___ ___ ___ cer An organism that makes its own food.
4 auto ___ ___ ___ ph Another name for a producer.
5 consu___ ___ ___ An organism that does not produce its own food.
6 heter___ ___ ___ oph Another name for a consumer.
7 ca___ ___ ___ vore An organism that eats another animal.
187 Chapter 7 Ecology
Sci-words
8 omni ___ ___ ___ ___ An organism that eats both plants and animals.
9 her___ ___ vor ___ An organism that eats plants only.
10 f___ ___ d ch ___ ___ n The nutritional sequence in a habitat.
11 f___ ___ d w ___ b The interaction of a number of food chains.
12 bio ___ ___ ___ ___ ___ sity The number of different organisms living in a community.
13 org ___ ___ ___ ___ matt___ ___ All the material in the biosphere that comes from living organisms. It contains theelement carbon.
14 d___ ___ ___ ___ posers Those organisms that break down dead material.
15 mutu___ ___ ism A relationship between two species, where each benefits.
16 commen___ ___ ___ ___ sm A relationship between two species where one benefits from the interaction, whilethe other is unaffected.
17 para___ ___ ___ ___ ___ ___ An exploitative relationship where one organism lives on or in another, causing thehost organism some harm.
Unit 7.4 The effects of human civilisation on ecosystems
Word Clue
1 poll___ ___ ant Something that makes the environment unhealthy.
2 glo___ ___l w___ ___ ___ ing The term used to describe the Earth’s rising temperature.
3 gr___ ___ ___ h___ ___ se ef___ ___ ___ ___ This is due to the formation of a thick blanket of gases surrounding ouratmosphere, which is trapping heat inside it.
4 ac___ ___ ra ___ ___ Rain that is polluted with chemicals, making it acidic.
5 tran___ ___ ___ ___ ation The process whereby trees remove water from the soil, releasing it back into the atmosphere through the leaves as water vapour.
6 over___ ___ ___ zing When too many animals are allowed to graze in one area, causing the area to bedestroyed.
7 de___ ___ ___ est ___ ___ ___ ___ ___ The large scale removal of trees from an area.
8 ex___ ___ ___c spe___ ___ ___ s Organisms that are introduced into an area.
9 con___ ___ ___ vation The process of doing what is necessary to keep plant and animal species alive.
