CHAPTER 7
REVIEW QUESTIONS
7.1
a.
b.
c.
d.
i. Each of the three species is showing a clumped distribution, being found only in
particular parts of the area.
ii. fern = 30 ÷ 100 m2 = 3 ÷ 10m2
wattle = 24 ÷ 100m2 = 2.4 ÷ 10m2
eucalypt = 3 ÷ 100m2
Ferns require moist areas thus it is likely that the area in which they are found is either a
watercourse or a shaded gully. That the eucalypts are found only in the bottom left of the
plot suggests that the land slopes upwards from the area of the ferns. The soil at this point
is probably deeper to allow root penetration by the eucalypts, with good drainage. The
eucalypts and wattles, which require good sun, would provide shade for the ferns.
There are more ferns than other species.
Fernland or fern-wattle community.
7.2
In both the J-shaped and S-shaped population growth curves, the growth is initially slow. Then,
as numbers of breeding adults increase, the growth becomes very rapid. At this point the two
growths differ. In the J-shaped growth pattern, this rapid growth is suddenly reversed, with a
rapid drop in the population as resources are deleted and the organism either disperses or goes
into a dormant phase. In the S-shaped population growth situation, as the resources start to
become depleted by the species, environmental resistance slows the growth until population
numbers become stable so that the number of individuals and the resources are balanced.
7.3
Density dependent: food supply, water, shelter (nest sites), predators, parasites, disease.
Density independent: weather conditions (e.g. temperature, winds, storms, seasonal changes).
7.4
a.
b.
c.
7.5
a.
b.
c.
7.6
a.
b.
c.
7.7
Birth rate, death rate, immigration and emigration.
r = (b + 1) – (d + e)
= (870 + 601) – (1700 + 240)
= 1471 – 1940
= -469
Thus the population decreased from 2000 to 1531 individuals.
Rate of change = -469 per 2000 = -235.5 ÷ 1000
Homeostasis: maintenance of a constant internal environment. In relation to population
size this would refer to the maintenance of a constant population size which is controlled
by environmental resistance.
Negative feedback: the reversal of a trend resulting in return to the optimum condition.
Environmental resistance: any environmental factor which prevents further increase in
population size.
Niche: the ‘role’ of an organism in its habitat which is related to its resource
requirements.
Resource partitioning: the division of environmental resources by coexisting species so
that the niche of each species differs in at least one significant resource.
Character displacement: a difference between two species which occupy the same habitat
which ensures that their niches are not identical.
Two species cannot simultaneously occupy the same niche in the same place for very long.
7.8
Each of these species will have some significant difference in at least one resource. One
species might use a slightly different part of the habitat: e.g. insectivorous species of birds,
where some species hunt in the lower foliage of trees, some amongst the bark of the trunks and
others on the high foliage.
7.9
Increase: any factor which reduces environmental resistance, such as change in climatic
conditions. E.g. good rain can lead to an explosion of plant growth. This in turn can lead to an
explosion of species of animals dependent on that growth..
Decrease: any factor which increases environmental resistance, such as stress from
overcrowding, depletion of resources, climatic conditions.
7.10
It takes too long for the predator numbers to increase to the point that they would control an
explosion of prey numbers. It has been suggested that the predators probably only change the
age structure of the population, taking the young, diseased and aged members that are more
readily captured. It is more likely that stress of overcrowding or a time lag in response to
density-dependent factors would control such population explosions.
7.11
Improved technologies, e.g. the use of tools, the agricultural revolution and the scientificindustrial revolution.
7.12
Suitable climate, water, food, shelter, presence of mates. These factors are the same as those of
the red kangaroo. However, due to technological advances, many of the world’s human
population are no longer directly dependent upon climate, water, food and shelter: food can be
grown in suitable areas and transported from anywhere in the world, water is stored in large
reservoirs and piped to shelters which humans construct. Shelters can be heated in cold
climates and cooled in hot climates. Diseases and parasites can be controlled to a large extent
by medical technology.