Topic 2 The Ecosystem
Notes Ch. 2 Part 3
2.6- Changes, 2.7 – Measuring Changes
2.6- Changes pp. 55-72
1. Limiting Factors and Carrying Capacity
a) List the limiting factors for population growth:
b) Define carrying capacity :
c) Explain the example of certain savannah seeds and temperature:
d) List some examples of how temperature is a vital limiting factor with
animals:
e) Explain fig. 2.39
1
2. S – and J – Curves
a) Explain this curve
Fig. 2.41 a
b) Explain this curve
Fig. 2.41 b
2
c) Read ch. 1 p.7-8 below and make sure you understand positive and
negative feedback :
Positive feedback – goes up and up and up
2000
1995
1990
1985
1980
1975
325
320
1970
CO 2
concentration
/ ppm
375
370
365
360
355
350
345
340
335
330
Year
3
Negative Feedback – key word : Fluctuates
4
d)
List the factors that affect the following stages of an S- curve:
1. Exponential growth phase –
2. Transitional phase –
3. Plateau phase –
Notes about Carrying Capacity – See IB 1



It Is greater for populations with high reproductive rates
Death rates increase and birth rates decrease
Animal populations can exceed carrying capacity with unsustainable use
of resources ( overshoot) but will eventually die back to normal carrying
capacity. Over shoot can also be caused by positive feedback dieback
can be caused by negative feedback.
IB 1 The carrying capacity of an environment for a given species
A.
can never be exceeded.
B.
is greater for a population with a slow reproductive rate.
C.
is achieved when birth rates equal death rates
D.
can only be exceeded with unsustainable use of resources.
IB 2 The main difference between ‘S’ and ‘J’ population growth curves is that
A.
‘S’ curves demonstrate exponential growth.
B.
‘J’ curves demonstrate exponential growth.
C.
‘S’ curves reach no stable maximum.
D.
‘J’ curves reach no stable maximum.
IB 3 As disease spreads through a population, numbers fall. As the result of a reduction in
contact between individuals, the rate of spread of the disease is reduced. This is
followed by a recovery in numbers.
5
This is an example of
A.
positive feedback
B.
negative feedback
C.
demographic transition
D.
entropy
3. Density – dependent and Density – independent
factors pp. 60 - 61
a) Density dependent – limiting factors – summarize:
Examples : predator – prey relationships a type of negative feedback : Prey
increases and so does predator but this may cause negative feedback in which
prey decreases and predator decreases, thus creating a cycle .
6
b) Density independent – limiting factors – summarize:
Viruses : density dependent, independent or both?
Read the following and determine if the virus was either density dependent or
independent . Explain why.
Case 1 : The introduction of European rabbits into Australia resulted in a
population explosion to around 600 million animals. In 1950, the government
sanctioned the release of myxomatosis virus and cut the population to 100
million. The virus was not contagious, it just acted as a general poison to kill the
rabbits.
7
Case 2 : By 1991 the rabbits of Australia became resistant to the virus and the
population returned to 300 million. The government released a second virus, the
calicivirus. Where there was a greater density of rabbits, the virus was more
lethal than where the population was lighter.
Internal and External Factors – define and give examples
a) Internal - density dependent fertility or size of breeding territory.
b) External – predation or diseases that affect population; water, temp.
nutrient availability
Interspecific vs. Intraspecific competition : explain the difference
Interspecific – between different species Intraspecific – within the same species
IB 4 A parasite, infecting the organs of its host, spreads from host to host more rapidly
when the host population, in a given area, is higher. Assuming infection with the
parasite reduces fertility, this would be an example of control of the host population
through.
A.
an external, density independent factor.
B.
an internal, density dependent factor.
C.
an external, density dependent factor.
D.
an internal, density independent factor.
4. Survivorship curves : K , r and C strategies
a) List basic characteristics and examples of K , r and C:
b) know table 2.1
8
c) Survivorship curves fig. 2.46 p. 63 : explain
IB 5 Which statement most correctly describes K-strategist organisms?
A.
They reach adulthood quickly and have many young.
B.
They reach adulthood slowly and have many young.
9
C.
They reach adulthood quickly and have few young.
D.
They reach adulthood slowly and have few young.
5. Succession – carefully read pp. 64-65
a) Definitions :
1. pioneer community –
2. sere –
3. primary succession4. secondary succession 5. climax community –
A Model of Succession on Bare Rock
10
IB 6 (a)
Explain what is meant by the terms ecological succession, pioneer community
and climax community.
(6)
11
(b)
For a named ecosystem, describe how the abundance of the different species
of organisms present changes during the various stages of succession.
(5)
(c)
Describe and explain how gross primary productivity changes during the
stages of succession.
(a) ecological succession
 the (orderly) process of change over time in a community/ecosystem
 changes in organisms may be associated with changes in
abiotic environment (e.g. soil, microclimate)
 successive communities displace each other through competition
e.g. volcanic island developing into tropical rainforest
pioneer community





the first organisms to colonize a new environment
usually dominated by producers/plants
usually dominated by r-strategists
pioneer communities often very simple in structure/low diversity
tolerate harsh conditions e.g. strong light/low nutrient levels
e.g. community of lichens covering bare rock (lithosere)
climax community




(b)
the end-point of ecological succession in equilibrium/relatively stable
may have a high level of complexity
usually dominated by K-strategists
characteristics of climax community determined by climate and soil
e.g. mature woodland/rainforest ecosystem;
name of ecosystem;
e.g. sand dune succession on coast of Western Australia
Name must be reasonably detailed, e.g. “freshwater” is not insufficient.




pioneer species very low in number initially but numbers
increase rapidly with lack of competition then decrease later as
other species displace them
changing abundance follows a J-curve
eventually climax species become established and the numbers
increase slowly to maximum/carrying capacity
changing abundance follows an S-curve
12
(c)

gross primary productivity (GPP) – the total amount of organic
matter produced/solar energy fixed by photosynthesizing plants

gross productivity initially absent/very low due to initial absence of
photosynthesizing organisms

increases through pioneer stage as colonization by
photosynthesizing plants increases

as green plant biomass increases, gross primary productivity
increases

GPP usually at its maximum at climax;
IB 7 In the process of succession, earlier communities disappear because
A.
they are displaced through competition.
B.
their gross productivity decreases with age.
C.
they eventually produce disadvantageous changes to their physical
environment.
D.
their biodiversity is low.
IB 8 Ecological succession generally involves
I.
a decrease in the ratio of organic to inorganic storages
13
II.
loss of communities through competition.
III.
an increase in the ratio of organic to inorganic storages.
A.
III only
B.
I and II only
C.
II and III only
D.
I, II and III
6. Changes in Succession , Gross Productivity –
Net Productivity, Climax Communities
a) Know table 2.2
14
b) Gross Productivity – Net productivity
Read top of p. 68 carefully and Review Gross productivity and Net
Productivity .
Gross productivity ( GP ) – total gain by all organisms - PRODUCERS ,
CONSUMERS
Net productivity ( NP) - total gain by all organisms - PRODUCERS ,
CONSUMERS AFTER respiratory loss ( R) .
NP = GP – R
Summarize top of p. 68 :
Climax Communities read p. 69 know all
15
IB 11 Compared to pioneer communities, climax communities usually have
A.
a lower gross productivity.
B.
a higher gross productivity.
C.
inverted pyramids of biomass.
D.
shorter food chains
2.7- Measuring Changes along an ecological gradient
pp. 73-74
a) Definitions:
1.
2.
3.
4.
5.
6.
Ecological gradient Quadrat method Line transect –
belt transect –
continuous transect interrupted transect –
b) Explain fig. 2.56
16