Section 1.2 Local Ecosystems Further Questions and Answers

Section 1.2 Local ecosystems – Further questions and answers

Q1.

Bk Ch1 S1.2 FQ1

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.

A1.

Bk Ch1 S1.2 FA1

The ants benefit from the relationship by obtaining shelter and nesting space from the epiphytic plant. The relationship between the ants and the epiphyte is called mutualism because both kinds of organisms benefit from the relationship. This is an example of mutualism and not commensalism because the plant would not otherwise survive in the area without the nutrients it obtains from the ant nest in its stem.

Q2.

Bk Ch1 S1.2 FQ2

Complete the table 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.

Organism / Feature / S, B or P? / Benefits for organism
Grey mangrove / Pneumatophore
Coast saltbush / Halophytic
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 Heinemann Biology, p.22)

A2.

Bk Ch1 S1.2 FA2

Organism / Feature / S, B or F? / Benefits for organism
Grey mangrove / Pneumatophore / S / Allows gaseous exchange between roots and air
Coast saltbush / Halophytic / F / Tolerant of salty environment
Red kangaroo / Licks forelimbs in hot weather / B / Evaporation of saliva from skin surface is a cooling mechanism
Three-lined skink / Basks in sun during cool weather / B / Increases body temperature
Common wombat / Retreats to burrow on a hot day / B / Reduces heat gain and water loss through evaporation from skin surfaces
Blackbutt / Releases a chemical into soil / F / Inhibits germination of seedlings close to parent plant

Q3.

Bk Ch1 S1.2 FQ3

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.

A3.

Bk Ch1 S1.2 FA3

a 98.8 ¸ 0.014 = 7057 times

b DDT has a detrimental effect on reproduction in birds. It results in thin, brittle egg shells that break before chicks are ready to hatch. This reduces the number of viable offspring in birds. The peregrine falcon is an example of a top-order consumer that was affected by DDT last century. Its numbers declined dramatically due to the effects of DDT on its eggs. Since the use of DDT was abandoned for agricultural purposes the population of the peregrine falcon has increased.

c If top-order consumers die out as a result of DDT poisoning there would be an initial increase in the population size of other organisms, because their predators have been removed. However, an increase in the population size of organisms leads to more competition for available resources such as food and shelter. This would eventually lead to a decrease in population sizes of these organisms.

Q4.

Bk Ch1 S1.2 FQ4

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?

A4.

Bk Ch1 S1.2 FA4

a The Sun

b Producer organisms harness the Sun’s energy in the process of photosynthesis. In the presence of sunlight they combine carbon dioxide and water to produce energy-rich glucose molecules that all organisms need. Consumer organisms do not photosynthesise.

Q5.

Bk Ch1 S1.2 FQ5

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.

A5.

Bk Ch1 S1.2 FA5

a Producers: algae (phytoplankton).

Primary consumers: zooplankton.

Decomposers: none shown.

Top-order consumer: Human.

b i algae ® zooplankton ® seal

ii algae ® zooplankton ® fish ® seal

c Food chains are simple linear feeding relationships. When one organism is removed from the food chain the food chain disintegrates. However, in a food web, when one kind of organism is removed there are usually alternative food sources for the organisms in the next trophic level. The food web will be affected but it is not likely to disintegrate. For example, in the food web shown, if the population of small fish is removed, the seals and humans that consume the small fish have other food sources in the food web.

Q6.

Bk Ch1 S1.2 FQ6

Write out a food chain in which you are a link. What niche do you occupy?

A6.

Bk Ch1 S1.2 FA6

Answers will vary. Food chains must begin with a producer.

Q7.

Bk Ch1 S1.2 FQ7

Using library and Internet resources, investigate the Earth’s growing human population. Discuss the implications, problems and solutions, from an ecological viewpoint.

A7.

Bk Ch1 S1.2 FA7

The Earth’s human population has already exceeded its natural carrying capacity and our population is growing. This has enormous implications for our global ecosystem. Humans need land for living and for agriculture to provide food. Land needs to be cleared to sustain ourselves. However, a growing human population together with its urbanisation and industry means an increased amount of carbon dioxide in the atmosphere. Clearing land of trees, shrubs and grasses—valuable resources in terms of replacing oxygen in the atmosphere through photosynthesis—will only serve to compound the problem. Clearing land of its natural ecosystems also reduces biodiversity.

One possible solution to the problem of feeding our growing human population is to increase the consumption of primary produce. Since primary producers are the first organisms in food chains, and the site of carbohydrate production, they represent the organisms with the highest levels of energy and the most efficient form of food. This would mean less land needs to be cleared for grazing cattle and sheep, for example.

Note: Many responses would be appropriate here. Key terms for library or Internet searches include ‘human population’, ‘global ecology’ and ‘ecological footprint’.

Q8.

Bk Ch1 S1.3 Q8

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?

A8.

Bk Ch1 S1.3 A8

a Since European settlement of Australia in 1788 more than 50% of eucalypt forest and over 75% of rainforests have been cleared or affected by activities such as logging.

b Forests are cleared for many reasons, including to provide space for farmland, urbanisation and roads.

Q9.

Bk Ch1 S1.3 Q9

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.

A9.

Bk Ch1 S1.3 A9

a ‘Biological control’ means the introduction of a predator or parasite to control a pest species.

b The cane toad has become a pest species in Australia because it is a prolific breeder, has no significant predators and has few competitors or parasites.

c As well as preying on cane beetles, the cane toad feeds on native insects, successfully competing against other native species for food. This means that the cane toad population has not been confined to the cane fields of Queensland, but has expanded to the Northern Territory and New South Wales. This has led to an increase in the population of the introduced cane toad and a decrease in the numbers of competing native species over a wide area of Australia. The cane toad has no natural predators in Australia to keep its numbers in check. Its poison glands result in the death of would-be predators.

Q10.

Bk Ch1 S1.3 Q10

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.

A10.

Bk Ch1 S1.3 A10

a The prickly pear cactus was introduced into Australia early last century. Being well suited to Australian conditions and with no natural controls, it spread rapidly and by 1925 covered eight million hectares of farmland in Queensland and northern New South Wales.

b In 1925 the Argentinian moth Cactoblastis cactorum was introduced as a biological control. The larvae of this moth specifically eat the prickly pear cactus. This measure proved to be successful. Today only small pockets of the prickly pear cactus remain.

1.2 Local ecosystems FQA page 1 of 4