ANSWERS TO REVIEW QUESTIONS – CHAPTER 45
1.
Biologists and conservationists are concerned about the ‘biodiversity crisis’. What is
biodiversity and why is its conservation considered important? (pp. 1113–1117)
Biodiversity is the variety of all forms of life, the diversity of genes they contain and the ecosystems of
which they are components.
The text gives five reasons for conserving biodiversity:
1.
2.
3.
4.
5.
Ecological— Organisms play roles in ecosystems that may be essential for ecosystem survival.
Practical—Organisms can be used for human benefit for food, medicines, timber, recreation, and
so on.
Aesthetics—People appreciate and enjoy wild organisms and wild places.
Philosophy—Should a species be driven to extinction if human intervention can save it? Do other
species have as much right to exist as humans?
Custodial—Nations preserve their cultural heritage in museums, by protecting old buildings and
by passing on the best of their art and literature. It can be argued that they have an equal
responsibility to conserve and pass on their biological heritage for the enjoyment of future
generations.
2.
What are feral animals? Name three feral animals found in your region and research the
impact of one of these species. (pp. 1119–1123)
Feral animals are either domestic animals that have escaped and run wild or those introduced for
biological control and for recreation. Students asked to name or research a feral animal almost
inevitably name a vertebrate. However, other animals such as insects may become feral. For example,
the European honeybee Apis mellifera is now feral in Australia. It may cause considerable impact by
displacing native pollinators and nesting in tree hollows that would otherwise be shelters to native
animals.
3.
Why was the cane toad introduced into Australia? What factors led to its population
‘explosion’ and range expansion? (pp. 1120–1121 Box 45.3)
The cane toad was introduced into Queensland, Australia, in 1935 to control two native pests of sugar
cane. It failed as a biocontrol agent, but thrived because of the ready availability of native invertebrates
and small native vertebrates as prey. Cane toads increased rapidly in both numbers and range because
of their reproductive potential and their broad diet. They tolerate variations in water salt content better
than other Australian frogs, breeding and surviving in brackish water. The female produces many
thousands of eggs and needs very little free water in which to breed. The eggs hatch quickly and the
tadpoles mature more rapidly than many Australian frog species.
Cane toads have few worries about food availability because of their very broad diet. In suburban areas
they are known to congregate at streetlights to catch insects attracted to the light and to steal food from
pet bowls.
4.
What is a weed? What are some of the characteristic features of weedy plants? Explain why
a plant that is not a problem in its native country can become a serious weed when
introduced into another country. (pp. 1119–1123)
Weeds are plants growing where they are not wanted, which makes the definition of a weed very much
a matter of perception. Weeds are opportunistic, often producing many seeds that germinate under a
wide range of conditions. The seedlings grow quickly and reproduce early, often using asexual
vegetative reproduction for rapid increase in numbers. They are especially likely to infest land
disturbed by fire, clearing or livestock grazing. Plants which are not a problem in their native country
may become weeds when introduced elsewhere because the competitors and predators that hold them
in check are absent in the new environment.
5.
Why are agricultural soils more susceptible to erosion than tree-dominated soils? (pp. 1123–
1130)
Erosion is the loss of soil caused by wind and water. In woodlands and forests soil is stabilised by the
dense mat of plant roots and the plants themselves provide windbreaks. Fallen leaves and other organic
matter further stabilise the soil, so that rainfall tends to soak in rather than flow across the surface.
Agricultural soils are not protected in similar ways, especially after harvesting or when pasture dies
back during drought. Livestock may also compact agricultural soils, increasing water flow and erosion
after rain.
6. What is soil acidification and what causes it? (pp. 1123–1130)
On the pH scale of acidity, values of 7.0 are neutral and those less than 7.0 are acidic. The yields of
many agricultural plants decline when soil pH falls to 5.0 or less. Ammonia-based fertilisers are added
to many Australian agricultural soils to correct for low levels of soil nutrients, or pastures are sown
with legumes that grow well in nutrient-poor soils. However, these measures increase soil acidity.
7.
What is dryland salinity and what causes it? How can the planting of native vegetation help
to reduce salinity? (pp. 1123–1130)
Dryland salinity is the increase in salt levels in surface soils that results from agricultural clearing.
Trees transpire large amounts of water and water is also lost from the soil surface by evaporation. The
balance between these two water uses and the addition of water by rainfall determine the level to which
water rises in the soil. When tree cover is removed in agricultural clearing, water loss from the soil is
reduced greatly and the watertable rises, carrying salt from deep in the soil with it. Once the watertable
is within 2 m of the surface, salt is carried to the surface by capillary action. Salt remains as the water
evaporates.
8.
Port Phillip Bay in Victoria is not completely flushed out by tidal changes. In the 1980s, the
Bay experienced red tides, blooms of dinoflagellates (see Chapter 35). Suggest reasons for
these algal blooms. Why are algal levels monitored where there are mussel farms? (As well
as Chapter 35, students should review the phosphorus and nitrogen cycles in Chapter 44.)
The major reason for algal blooms in Port Phillip Bay was an increase in dissolved inorganic and
inorganic nutrient concentrations associated with human activity.
Algal levels are monitored near mussel farms because some algae, such as dinoflagellates and
cyanobacteria, synthesise toxic compounds. At high concentrations these toxic compounds may be
harmful to vertebrate health. Filter-feeding bivalves (mussels) which use algae as their primary food
source accumulate the algal toxins in their tissues. When higher-order organisms, such as humans, feed
on the mussels, the toxins can be passed on and cause poisoning. The physiological symptoms of
shellfish poisoning range from mild stomach upsets to severe neurological conditions
9.
Briefly explain the ‘greenhouse effect’, naming the major causes. List the positive and
negative results of the greenhouse effect. (pp. 1128–1129)
Heat-absorbing atmospheric gases such as CO2, N2O and CH4 in the atmosphere trap solar radiation
reradiated from the surface of the earth, thereby warming the lower atmosphere. This natural process is
the greenhouse effect. Without it, global temperatures would average 30 oC less than at present.
However, the enormous increase in the burning of fossil fuels that accompanied the Industrial
Revolution of the nineteenth century elevated greatly the levels of all these greenhouse gases. These
increases enhance the greenhouse effect and, by warming the earth further, may cause global climate
change.
10. What are the key factors to consider when restoring highly modified natural systems? List
five of these. (p. 1132)
1. Restore what is left.
2. Gather information on the habitat requirements and movement patterns of species of functional or
conservation value.
3. Breeding programs for rare and endangered species.
4. Incorporate disturbance regimens, such as burning, to ensure different successional patterns.
5. Cost-effective methods of replanting.
6. Incorporate fungi and soil microorganisms from unmodified systems.