Human impacts on ecosystems

Which of these statements best describes the role of organisms in ecological succession?

• Organisms can change both their biotic environment and their abiotic environment.

• Organisms can change their biotic environment but not their abiotic environment.

• Organisms can change their abiotic environment but not their biotic environment.

• Organisms can change to meet the demands of their environment.

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When a dirt road falls into disuse, annual weeds soon begin to grow on it in increasing numbers. Eventually these weeds are no longer evident, as perennial grasses overgrow the area. The biological principle that best explains this situation is:

• energy pyramids

• ecological succession

• cycling of matter

• ecological equilibrium

When succession occurs, the species present change because:

• the early species exhaust the food supply and die out.

• different species take different lengths of time to develop.

• each community alters the environment, enabling other organisms to become established.

• the change in climate from season to season creates different physical environments, suiting different species.

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Which of the following is NOT an example of primary succession?

• Grassland growing on the site of a previous rainforest that has been cleared

• Lichens growing on rocks

• moss growing on mountain cliffs

• pioneer plants colonising the new land formed from a lava flow

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The eastern grey kangaroo is a marsupial found in southern and eastern Australia, with a population of several million. It is predominately a grazer, eating a wide variety of grasses. Kangaroo populations have increased dramatically since European settlement and the eastern grey kangaroo still covers the entire range it occupied when Europeans arrived in Australia. Which of the following could account for the increase in eastern grey kangaroo populations since European settlement?

• The cutting down of forests to create grasslands for sheep and cattle grazing

• The introduction of foxes and the increase in numbers of feral dogs and cats that predate on kangaroos

• The overgrazing by sheep of many areas of grassland during times of drought

• The ability of pregnant eastern grey kangaroos to freeze development of an embryo until the previous pouch young is able to leave the pouch

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Many populations of native birds species have undergone serious decline since European settlement. Which factor would be least likely to have contribution to this decline?

• Reduced food supplies due to habitat destruction

• Increased competition from introduced species of birds

• Increased predation by native species of mammals and reptiles

• Reduced availability of suitable nesting sites.

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Succession is an important process in ecosystems. Select the best explanation from the following.

• Succession is influence by biotic factors, such as lichens breaking down bare rock, but not abiotic factors, such as the weathering of rock by the wind.

• During succession, plants gradually change over a long period of time, for example, shrubs growing taller and developing a single stem and becoming a tree.

• The progress of succession is easily observed as it is obvious when one community is replaced by the next community at each stage of succession

• Secondary succession is usually much quicker than primary succession, as there is already an existing seed bank of suitable plants in the soil.

The koala is found in isolated populations, mainly in eastern Australia. It was once much more widely distributed throughout much of eastern and southern Australia, but it is now a threatened species in many regions. In trying to ensure the survival of this species, it would be best to:

• prevent further habitat destruction and protect adequate areas of suitable habitat.

• encourage tourists to visit the habitat of the species to make it economically valuable.

• carry out a captive breeding program for the species and reintroduce it to suitable areas.

• keep the species in captivity in metropolitan zoos and regional wildlife parks.

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Soil is a basic agricultural resource that is often affected by the actions of humans. Choose the best description from the following:

• Sheep and some other introduced domestic animals have soft feet, so they do not compact the soil when they graze.

• Sheep are selective when they graze, taking some plants in preference to others.

• With significantly reduced tree cover and an increase in shallow-rooted grasses, the topsoil can be lost because it becomes more exposed to wind and rain.

• Soil is considered a renewable resource because it is continually replenished by the weathering and erosion of rocks.

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