CHAPTER 9
EXTENDING YOUR IDEAS
1.
Once the rainforest canopy is removed, the humidity of the area decreases and evaporation
increases, thus many of the decomposer organisms adapted to the rainforest litter will not
survive. The rate of decomposition decreases. Initially the soil nutrient level is high but as the
crop plants deplete the nutrients they are not replaced (unless by artificial fertilisation) due to
the low rate of decomposition. The cost of application of fertiliser is probably so great that the
agricultural enterprise will not be viable.
2.
With increasing altitude there is decrease in temperature. Temperature changes influence wind
patterns, humidity (decreases with temperature) and rainfall (precipitation as ice and snow
with increasing altitude). Chemical reactions decrease with decreasing temperature. Thus
different plant communities, adapted to the specific temperature range of that altitude, will be
found with increasing height – changing from evergreen forest to deciduous forest to alpine
meadows and finally no plant growth.
Water is essential for life. Different plants have different adaptations for surviving within a
particular soil water range, e.g. mangroves and other wet area plants have adaptations for
reducing loss or gain of salts due to differences in soil and cell sap concentrations. Many
rainforest trees have drip tips with glands for secreting excess water, and a variety of
adaptations exist for plants living in low water areas, e.g. reduced leaves, hairy leaves, low
growth patterns etc. Thus the amount of rainfall is significant in the distribution and
abundance of specific plant species. Even if rainfall is high, however, the water may not be
readily available to the plants if the soil type is unable to retain it. Thus coastal plants, in high
rainfall areas but in sandy soil, will show typical heath, dry land adaptations. Similarly, if the
soil contains a large proportion of clay, water retention will be very high and the soil may
become waterlogged. In this case only those plants with adaptations (e.g. means of obtaining
oxygen for root activities) will be able to survive these conditions. The amount of rainfall also
determines the level at which decomposition can occur and thus recycling of nutrients back to
the soil for plant use.
The types and amounts of mineral nutrients varies from soil to soil. Certain mineral nutrients,
such as nitrates, phosphates, etc. are essential for plant growth. Different plant species vary in
their ability to extract particular nutrients from the soil. Those living in nitrate and phosphate
deficient soils invariably have nitrogen fixing bacteria or mycorrhizae living in a mutualistic
relationship with them. Thus nutrient availability determines the distribution and abundance of
plant species.
Altitude therefore affects temperature, rainfall and other abiotic conditions. The soil type
determines water retention and nutrient levels. Different plants are adapted to a specific
temperature range, soil water and nutrient level. Thus different plants will be found in
different places due to changes in these conditions.
3.
The Simpson Desert would be extremely hot in the day time and cold at night. There would be
little water available and sparse plant food. Thus most of the animals would be small
(providing a small surface area to volume ratio to minimise water loss) and have some means
of getting rid of excess heat if they are active during the day (e.g. large ears if a mammal).
Mammals, which are able to maintain a constant body temperature, would probably be
nocturnal, feeding in the cool of the night when the rate of evaporation is low, on either seeds,
the sparse grasses or insects. Their hair would help maintain body temperature at night. They
would probably burrow or find crevices in rocks, etc. during the day and remain inactive, thus
decreasing water loss. Insects and lizards are probably active during the early morning and
late afternoon, when environmental temperatures are high enough to raise their body
temperatures for activity but not high enough to cause high water loss. Their body covering
would be such as to minimise water loss (hard water-retentive cuticles in insects which reflect
solar energy; scales in lizards and snakes). For most of the year the birds would be
insectivorous or carnivorous (owls at night feeding on small mammals and snakes; eagles and
hawks active during the day feeding on lizards, snakes and insects). After good rain, and with
the short period of massive ephemeral plant growth, other birds such as small parrots would
probably migrate into the area. All animals would have to have means by which to extract all
available water from the food they eat (e.g. seeds and other small animals), to retain all water
from metabolic activities and to produce a very concentrated urine.
Thus by structure, physiology and behaviour, the adaptations of these organisms enable them
to survive in this very harsh environment.
4.
In a stable forest there is little growth. Photosynthetic activity, therefore, occurs at a rate
which maintains stable growth and stores adequate food for adverse conditions, repair (from
the activities of herbivorous animals and natural attrition) and reproduction. The plants respire
constantly and so release carbon dioxide. Decomposer organisms and the animals dependent
upon these stable forests also release large amounts of carbon dioxide. Thus the overall uptake
of these forests is probably equal to the release of carbon dioxide from the forest community.
It is a balanced ecosystem. In a young, growing forest, the rate of growth is very high and it
will not support as large an animal population as a mature forest. As a consequence carbon
dioxide uptake will be greater than carbon dioxide release.
The removal of stable forests, although causing massive ecosystem changes, does not in itself
increase carbon dioxide in the atmosphere and thus global warming. What happens to the
fallen timber does, however, increase carbon dioxide levels in the atmosphere. The production
of usable timber products from the logs involves the use of machinery which operates on some
form of energy, such as burning of petrol or diesel fuel, burning of coal to produce electricity,
or muscle power which requires high food intake, all of which release carbon dioxide into the
atmosphere and use oxygen. Much of the tree is burned, further increasing carbon dioxide and
decreasing atmospheric oxygen. Immediately after forest felling the rate of decomposition also
probably increases for a short time. The increase in global warming resulting from increased
carbon dioxide levels in the atmosphere is most likely caused by human industrial activities
and increased transport, all of which are dependent on the burning of fossil fuels.
5.
a.
b.
6.
a.
b.
7.
a.
b.
8.
a.
b.
i. Avicennia 2 mg NaCl/10cm3 secretion; 2 gm NaCl/litre sap concentration.
ii. Lumnitzera 0.05 mg NaCl/10cm3 exclusion; 0.05gm NaCl/litre sap concentration.
Lumnitzera, Rhizophora, Sonneratia and Bruguera all have a sap concentration of less
than 0.4 gm NaCl/litre and are salt excluders. Aergiceras, Avicennia and Aegialitis have
sap concentrations of greater than or equal to 2 gm NaCl/litre and are salt secretors. Thus
ability to withstand a higher sap concentration of NaCl determines whether or not the
plant is an excluder or a secretor.
Closer to loam than clay; closer to silty clay loam than to sandy clay loam; closer to silt
loam than to silty clay loam.
Sandy loam.
Since most of the seeds found in the cassowary dung germinated, it is probable that the
seeds are adapted to digestion by the cassowary and might in fact require the action of
the digestive juices to activate germination. The cassowaries travel large distances in the
territories (5 km2 per pair). Thus the cassowaries are significant in the distribution of
these rainforest plants. The seeds are carried away from the parent plant where
competition for resources will be reduced, and deposited in their own patch of fertiliser
which will aid germination. If the dung has been dropped in an area where there is
adequate light (e.g. a break in the canopy), the germinated plant will be able to grow to
mature size.
Since each pair of cassowaries occupies a territory of 5 km2, increased land development
with consequent disruption of areas of rainforest will result in fewer cassowaries. Since
these birds are significant in the dispersal of rainforest seeds and thus the maintenance of
the rainforest, over time it is likely that new plants will not replace trees lost to age,
disease and natural events. Over time the species composition and thus the entire
rainforest community will be seriously compromised.
2 dandelions in 0.25 m2 = 8/m2
100 m x 50 m = 5 000 m2
There are 3 daisies in 0.25 m2
Thus in the entire lawn there are 3 x 4 x 5000 = 35 000 daisies.
9.
a.
→
→
→
b.
Need to show:
out-competes other organisms
 rapid growth
 reproduces from cuttings
 wide tolerance to water temperature
 grows in a wide range of habitats, from surface to lower limits of rocky shores
(fragmentation results in further spread) to estuaries
 efficient extraction of nutrients even in very low nutrient areas
 produces a potent toxin in high concentrations which inhibits being eaten by all
marine herbivores
decreases all organisms since there is little other food for the first order consumers
marine meadows are breeding grounds for oceanic species, thus there is an overall
decrease in fish in surrounding deepwater areas
Small areas can be treated with chlorine gas – better to kill all organisms in one small
area than the consequences of mass death over a large area if the alga is allowed to
spread.
There is the possibility of biological control but more research is needed.
Ban the use of Caulerpa in all marine aquaria to prevent further accidental outbreaks.
Ban the movement of fishing vessels into and out of infested marine meadows to
prevent fragmentation and further spread of Caulerpa.