IB HL Biology: Ecology Review
Populations
1. Define the following terms associated with population ecology; population and carrying capacity.
2. What processes contribute to changes in population size?
3. What are some factors which can increase the carrying capacity of a population? Decrease?
4. What is quadrat sampling? When would it be used?
Fall 2017
Communities
5. Define the following terms; community, autotroph, heterotroph, producer, primary consumer, secondary consumer, detritivore and
saprotroph.
6. What is the initial energy source for all communities?
7. Be able to read food webs and determine the trophic level of different species.
8. Choose 2 regions below and determine the Simpson’s Diversity Index value for these regions. Which region is more diverse?
A. An area of the Black Forest in Germany contains 134 pitch pines, 24 douglas firs, and 53 red pines.
B. A meadow contains 1532 chestnut oaks, 342 black cherry trees, 12 white ash trees, and 1022 yellow birches.
C. You school science classroom contains 12 beetles, 34 termites, 84 ants, 93 fleas, and 1 butterfly.
D. An African park contains 15 lions, 94 giraffes, 1000 wildebeests, 50 elephants, and 5 hyenas.
Choose more areas if you need more practice.
9. What is a keystone species?
10. Distinguish between primary and secondary succession.
Ecosystems
11. What is an ecosystem?
12. Explain the 10% rule of energy transfer. How is the energy lost between trophic levels?
13. Review the Carbon Cycle. What are the main sources of carbon dioxide on earth?
14. Review the Nitrogen Cycle.
15. Distinguish between Gross Primary Productivity and Net Primary Productivity.
16. What is the Greenhouse effect?
17. How have human activities influenced climate change? When did human activities begin to influence climate change? Why?
18. What are the most common greenhouse gases?
Human Impact on the Environment
19. What are invasive species? Why are they able to take hold in a new habitat?
20. Describe biomagnification. Name one toxin / substance that experiences biomagnification in the environment.
21. Distinguish between In-situ and ex-situ conservation methods.
22. What impact do plastics have on ocean ecosystems?
PRACTICE PROBLEMS
1.. A researcher is trying to estimate the population abundance of Lodge Pole Pine Trees in Rocky Mountain National Park. He divides the park into
quadrats and counts the number of trees in a number of randomly selected quadrats. Below is a representation of his data.
Rocky Mountain National Park
5
9
2
8
11
2
5
8
8
9
3
7
2
2
4
6
1
5
7
What is the population estimate for Lodge Pole Pines in Rocky Mountain National Park?
What would you need to know and do to determine the density of trees in the park?
2. Another researcher is trying to estimate the number of Fox Squirrels living in Lakewood.
She uses the mark – recapture method to estimate the population size. The following data
was collected.
 Number of squirrels initially caught and released = 42
 Total number of squirrels caught in second sample = 23
 Number of marked squirrels in the second sample = 4
What is the population estimate?
3. During a several-year period of drought, the population abundance of mice, voles, rats and chipmunks in an oak forest remains at a relatively
constant, low level. Then a period of heavy rainfall ends the drought and results in a large increase in the population of acorns – a favorite food of
rodents. The rodent population during this year would be expected to
a. decline because of excess rainfall.
b. decline due to the competition from other species.
c. remain almost constant, with little or no variation.
d. increase in direct proportion to the increase in acorns.
e. increase much more rapidly than the increase in acorns.
4. A mouse population lives in a semi-desert environment that has been affected by global warming. In the past twenty years, temperatures in the
area have increased by an average of three degrees Fahrenheit, and rainfall has decreased by about five inches per year. Over this time period, it is
likely that the mice in this population have
a. grown larger and produced more offspring.
b. lived longer and produced more offspring.
c. gotten smaller and produced fewer offspring.
d. had shorter life spans and produced more offspring.
e. not changed; they are well adapted to any changes in the environment.
5. Sparrows eat both insects and seeds. To which trophic level do they belong?
a. primary consumer
b. secondary consumer
c. tertiary consumer
d. omnivore
6. Food webs describe the ______ within a community.
a. uptake of solar energy
b. distribution of organisms
c. flow of nutrients and energy
d. competition among organisms
7. Decomposers obtain energy from which trophic level or levels of a food web?
a. All levels
b. Omnivores only
c. All producers only
d. All consumers only
e. Secondary and tertiary consumers only
8. A rough measure of the flow of both energy and materials through ecosystems can be obtained by measuring
a. gross primary productivity
b. net primary productivity
c. output of biogeochemical cycles
d. geographic distributions of plants
e. flow through the hydrologic cycle
9. Complete the diagram of the nitrogen cycle by naming the organisms involved in processes A, B and C below.
N 2 in atmosphere
denitrification
Denitrifying
bacteria
(Pseudomonas
denitrificans)
C.
lightning
Proteins in
plants
feeding
Proteins in
animals
death
absorption
Fertilizers
excretion
A.
Nitrates in soil
decomposition
Ammonium
salts in soil
B.
Nitrites in soil
Nitrifying
bacteria
(Nitrosomonas)
(3)
10. The graph below shows the variation in the concentration of atmospheric carbon dioxide since 1970.
375
370
365
360
355
CO 2
concentration
/ ppm
350
345
340
335
330
325
2000
1995
1990
1985
1980
1975
1970
320
[Source: C D Keeling and T P Whorf, Atmosphere CO2 concentrations (ppm) derived from in situ air samples,
collected at Mauna Loa Observatory, Hawaii]
The annual fluctuation is mainly the result of changes in the levels of photosynthesis associated with the seasons
in Northern Hemisphere forests.
(a)
(b)
(c)
(i)
Describe the overall trend shown in the graph. (1)
(ii)
Suggest a cause for the overall trend throughout the period 1970–1999. (1)
(i)
(ii)
Using a clear label, identify any one point on the graph which shows the CO2 level in mid-summer.
Explain why the concentration of CO2 varies with the seasons. (2)
Identify one gas, other than CO2 , which is contributing to the enhanced greenhouse effect. (1)
11. Understanding the ecological mechanism that causes extinction is fundamental to conservation as not all organisms
are threatened by the same factors. A total of 1012 threatened bird species in 95 families were studied to see
how they were threatened by different factors:
habitat loss
persecution by humans and introduced predators
other factors (introduced competitors, hybridization and disease) and unknown risk factors.
Scientists investigated the relationship between body size and the risk of extinction, both due to habitat loss and to
persecution/predation. Birds were classified as small (mean body mass 1 to 1000 g) and large (mass greater than 1000
g). The results are shown in the pie chart and bar charts below.
Percentage of all 1012 species
threatened by each type of factor
20%
45%
10%
Extinction risk from habitat loss
6
5
Percentage of 4
species in
3
family at risk
2
1
0
Small
Large
Body size
25%
Habitat loss only
Habitat loss and predation / persecution
Predation / persecution only
Other / unknown
Extinction risk from persecution/predation
6
5
Percentage of 4
species in
3
family at risk
2
1
0
Small
Large
Body size
[Source: Modified from B Owens et al., Proceedings of the National Academy of Sciences, (2000), 97,
pages 12144–12148. Copyright 2000 National Academy of Science, USA]
(a)
(i)
State the percentage of species affected in some way by habitat loss. (1)
(ii)
Calculate the approximate number of bird species threatened by predation / persecution only. (1)
(b)
State two factors that could have caused habitat loss. (2)
(c)
Outline, using the bar charts, the effect of body size on the risk of extinction. (2)
(2)
(d)
Discuss the methods of conservation that would avoid the extinction of large species. (3)
5
–2 –1
2
12. The total solar energy received by a grassland is 5 × l0 kJ m y . The net production of the grassland is 5 × 10
–2 –1
2
–2 –1
–
kJ m y and its gross production is 6 × l0 kJ m y . The total energy passed on to primary consumers is 60 kJ m
2 –1
y . Only 10% of this energy is passed on to the secondary consumers.
(a)
Calculate the energy lost by plant respiration. (2)
(b)
Construct a pyramid of energy for this grassland. (3)
13.
The energy flow diagram below for a temperate ecosystem has been divided into two parts. One part shows
–2 –1
autotrophic use of energy and the other shows the heterotrophic use of energy. All values are kJm yr .
Autotrophs
autotrophic
respiration
photosynthesis
gross
production
43 510
Heterotrophs
heat 14 140
heat
23 930
net production
X
heterotrophic
respiration
feeding
14 690
storage
540
storage
4 900
(a)
Calculate the net production of the autotrophs. (1)
(b)
(i)
Compare the percentage of heat lost through respiration by the autotrophs with the heterotrophs.
(ii)
Most of the heterotrophs are animals. Suggest one reason for the difference in heat losses between
the autotrophs and animal heterotrophs. (1)
The heterotrophic community can be divided into food webs based upon decomposers and food webs based
upon herbivores. It has been shown that of the energy consumed by the heterotrophs, 99% is consumed by the
decomposer food webs.
(c)
State the importance of decomposers in an ecosystem. (1)
(d)
Deduce the long-term effects of sustained pollution which kills decomposers on autotrophic productivity.
14.
The diagram below is a simplified version of a food web from Chesapeake Bay. The arrows indicate the direction
of energy flow and the numbers indicate species within the food web.
At which trophic level or levels does species II function?
A.
2nd and 3rd consumer
B.
3rd consumer
C.
3rd and 4th consumer
D.
Producer
15.
Which is the best prediction about biomass?
A.
The biomass of X is more than the biomass of W.
B.
The biomass of X is less than the biomass of Y.
C.
The biomass of V + X + Z is equal to the biomass of W.
D.
The biomass of Y is less than the biomass of Z.
16 The diagram below represents an energy pyramid and four trophic levels.
IV
III
II
100 000 kJ m–2 yr–1
I
[Source: adapted from www.bio.miami.edu/dana/160/pyramid.gif]
16.
(i)
Identify the trophic level of the organisms indicated below. (2)
I.
...............................................................................................................
IV.
...............................................................................................................
(ii)
Calculate the approximate amount of energy in kilojoules transferred in m
level I to trophic level II. (1)
..................................................................................................................... kJ
–2
–1
yr from trophic
The diagram below is part of a carbon cycle diagram for an ecosystem in a pond.
(a)
(b)
(c)
State the names of the processes that
(i)
convert carbon dioxide into organic compounds in pond weeds and algae (1)
(ii)
convert organic compounds in pond weeds, algae and primary consumers into carbon dioxide. (1)
(i)
Draw arrows on the diagram above to show how the saprotrophs obtain carbon. (1)
(ii)
Explain the role of saprotrophs in recycling carbon. (2)
Draw a box on the diagram in an appropriate position, labelled organic compounds in secondary
consumers. Draw arrows to show the links between secondary consumers and other parts of the carbon
cycle. (2)
(2)
There has been a significant increase in the concentration of carbon dioxide in the Earth’s atmosphere during the
last fifty years.
(d)
(i)
Suggest two reasons for this increase in atmospheric carbon dioxide concentration.
1.
................................................................................................................
..........................................................................................................................
2.
................................................................................................................
..........................................................................................................................
(2)
(ii)
Suggest one effect of an increase in carbon dioxide concentration on organisms in a pond. Include in
your answer the reason for the effect and the type of organisms that are affected.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(2)
(Total 11 marks)