By destroying habitats and hunting without constraints we have caused the extinction of many species of animals and plants. The list of species at present threatened with extinction is a long one.
Conserving the environment is a global issue. In Australia, national, state and local governments, community groups and individuals are working to find the balance between human activities, the need to protect the quality of the environment and the need to conserve our unique plants and animals.
Since European settlement, more than 1900 plant species have been introduced into Australia from elsewhere. About half of these are now listed as weeds.
BIOFACT
FIGURE 1.40
The cane toad (Bufo marinus), a species from tropical South America, was intro-duced into Queensland in 1935 to control cane beetles in sugar cane crops. But the cane toad was no better than the native frogs at controlling the beetles, and became a pest itself. It breeds rapidly, has no major predators, and has few com-petitors or parasites. Its poison glands kill many would-be predators. It is rapidly extending its range into the Northern Territory and New South Wales. As it is a tropical animal, environmental factors such as cold and drought are currently the only controlling factors limiting its spread.
Environmental pests and weeds can be controlled by physical, chemical or biological means.
• Physical control includes shooting animals and cutting down or digging out plants.
• Chemical control includes use of poison baits and insecticides for animals and herbicides for plants.
• Biological control involves the
introduction of a predator or parasite.
FIGURE 1.41
In large cities such as Sydney, photochemical smog caused by gas emissions from vehicles and factories can be an extremely serious problem.
The Landcare movement has developed in Australia over the past 20 years as a partnership between landholders, land managers, industry and government. There are more than 1000 Landcare groups in New South Wales. These groups are concerned with managing all natural resources in their areas in a more sustainable way.
BIOFACT
The use of motor vehicles and the combustion of fuels such as wood and gas account for most of the air pollution in Australian cities.
BIOFACT
FIGURE 1.42
Most wastes from urban and industrial areas are dumped in tips without treatment.
In the past, polluting chemicals such as pesticides and paints were also dumped in this way, polluting the soil and water.
Pollution is the spoiling or poisoning of the environment through human activity.
Endangered Australian animals include:
● Baw Baw frog
● bent-wing bat
● bilby
● brush-tailed rock wallaby
● corroboree frog
● eastern bristlebird
● flatback turtle
● ghost bat
● giant freshwater crayfish
● giant Gippsland earthworm
● ground parrot
● helmeted honeyeater
● humpback whale
● Leadbeater’s possum
● mountain pygmy-possum
● northern hairy-nosed wombat
● numbat
● orange-bellied parrot
● speartooth shark.
BIOFACT
Q
Qu ue essttiio on nss
1 a What is a food chain?
b Write down an example of a food chain in an ecosystem.
2 a Define the terms ‘producer’ and ‘consumer’.
b Outline the role of each of the following types of consumers in ecosystems, giving one Australian example of each:
herbivore carnivore omnivore scavenger decomposer
3 a Define ‘biomass’.
b What information is expressed in a biomass pyramid that a food chain cannot express?
c Not all of the energy at one level of a food chain is passed on to the next level. What happens to it?
4 Describe each of the following kinds of relationships that exist between organisms in ecosystems, and give an Australian example of each:
i predator–prey ii parasite–host iii commensalism iv mutualism.
5 Outline some factors that can affect the numbers of predators and prey in ecosystems.
6 a Explain what is meant by the term ‘allelopathy’.
b Describe two examples of allelopathy, including at least one Australian example.
7 a Define the term ‘adaptation’.
b Describe an adaptation to an environmental factor displayed by
i an Australian animal ii an Australian plant.
38 Heinemann Biology
1 A particular epiphytic plant has a bulbous stem that is honeycombed with chambers. In these chambers lives a species of ant. The epiphyte obtains mineral nutrients from the ant nest in its stem, so it can survive in areas that cannot support other
epiphytes. Of what benefit is the relationship to the ants? What type of association exists between the plant and the ants? Explain your answer.
2 Complete the table (below) of adaptations shown by various plants and animals that make them well-suited to their particular environments. In each case, decide whether the adaptation is structural (S), behavioural (B) or physiological (P). Explain how the feature is beneficial to the organism.
3 Biomagnification is the increase in concentration of substances (such as DDT) at each level of a food pyramid.
a How much has the concentration of DDT
increased by the time it is taken up into the gulls’
tissues?
b Investigate how DDT affects birds, and
summarise your findings in less than 100 words.
c Suggest the possible consequences of DDT for other organisms as a result of its effects on top-order consumers.
4 a What is the original source of energy for any food chain or food web in an ecosystem?
b Why do all food chains begin with producer organisms?
5 Consider the food web in Figure 1.28.
a Identify the producers, primary consumers, decomposers, and top-order consumer.
b Draw a food chain for this food web that shows the seal in the position of
i secondary consumer ii tertiary consumer.
c Use an example from this food web to explain why food webs are more stable than food chains.
6 Write out a food chain in which you are a link.
What niche do you occupy?
7 Using library and Internet resources, investigate the Earth’s growing human population. Discuss the implications, problems and solutions, from an ecological viewpoint.
8 a Outline the impact of human activity on the extent of forest cover in Australia since European settlement in 1788.
b Why have Australian forests been cleared?
9 The cane toad is an example of an introduced species that was imported to Australia as a means of biological control. Unfortunately it became a pest itself.
a What is meant by ‘biological control?
b Outline the reasons that contributed to the cane toad becoming a pest.
c Describe the effects that this pest species has had in Australia.
10 Choose an example of an introduced plant that has become a pest in New South Wales.
a What effects has the pest species had in the state?
b Describe the successful measures, if any, that have been used to remedy the problem.
F
Red kangaroo licks forelimbs in hot weather Three-lined skink basks in sun during cool weather Common wombat retreats to burrow on a hot day Blackbutt releases a chemical into soil
(see p. 22)
herring gulls fish
shrimps in mud 0.014 ppm mud in Lake Michigan 0.44 ppm
4.4 ppm 98.8 ppm
DDT DDT concentration