1. C.5 Population ecology (AHL)
Essential idea: Dynamic biological processes impact population density
and population growth.
2. Understandings, Applications and Skills
Statement Guidance
C.5 U.1 Sampling techniques are used to estimate population size.
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited environment.
C.5 U.3 Population growth slows as a population reaches the carrying capacity of the
environment.
C.5 U.4 The phases shown in the sigmoid curve can be explained by relative rates of
natality, mortality, immigration and emigration.
C.5 U.5 Limiting factors can be top down or bottom up.
C.5 A.1 Evaluating the methods used to estimate the size of commercial stock of marine
resources.
C.5 A.2 Use of the capture-mark-release-recapture method to estimate the population
size of an animal species.
C.5 A.3 Discussion of the effect of natality, mortality, immigration and emigration on
population size.
C.5 A.4 Analysis of the effect of population size, age and reproductive status on
sustainable fishing practices.
C.5 A.5 Bottom-up control of algal blooms by shortage of nutrients and top-down control
by herbivory.
C.5 S.1 Modelling the growth curve using a simple organism such as yeast or species of
Lemna.
3. Populations
• The total number of individuals of a species in a given
area.
Populations are affected by four main factors
C.5 A.3 Discussion of the effect of natality, mortality, immigration and
emigration on population size.
4. Four Factors Influence the Size of a Population:
Natality: Birth Rate (offspring
produced and added to population)
C.5 A.3 Discussion of the effect of natality, mortality, immigration and
emigration on population size.
5. Mortality: Death Rate (individuals that die)
C.5 A.3 Discussion of the effect of natality, mortality, immigration and
emigration on population size.
6. Immigration:Immigration: Movement of members of the species into the areaMovement of members of the species into the area
C.5 A.3 Discussion of the effect of natality, mortality, immigration and
emigration on population size.
7. Emigration:Emigration: Movement of members of the species out of area to liveMovement of members of the species out of area to live
elsewhere.elsewhere.
C.5 A.3 Discussion of the effect of natality, mortality, immigration and emigration on
population size.
8. Population Changes
C.5 U.4 The phases shown in the sigmoid curve can be explained by relative rates of
natality, mortality, immigration and emigration.
9. Population size oscillates around the carrying capacity (K)
Time
N
K
overshoot
oscillations
C.5 U.2 The exponential growth pattern occurs in an ideal,
unlimited environment.
10. • Density Dependent Limits
Food
Water
Shelter
Disease
• Density Independent Limits
Natural Disasters
Humans (logging, mining, farming)
Water and shelter are
critical limiting factors in
the desert.
Fire is an example of a
Density independent
Limiting factor.
Limits on
Population Growth
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited environment.
11. C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
This graph shows the explosion of human population over the
last 10,000 years along with some relevant historical events.
12. How did we get here?
• When I graduated
high school there were
4 billion people.
*Today there are
almost 7 billion people
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
13. About 5 million years ago
Hunter-gathers
1 million people
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
14. Neolithic Period (6000 B.C.)
No longer a Natural Setting
100 million people
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
15. Common area 2000 years ago
300 million
people
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
16. 1800’s (Carbon cycle control)
Steam engineSteam engine
1 billion people
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
17. London between 1800 to 1880
• 1800 pop. 1 million
• 1880 pop. 4.5 million
• Improvements in medicine
and public health
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
18. Life Expectance
• Neolithic it was 20
• 1900 it was 30
• 1950 it was 47
• Current world average is 67
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
19. 1800-2000?
• From 1 billion to 6 billion? How???
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
20. 1908 Control of the Nitrogen Cycle
• Up until 1908 farms were
dependent on organic
sources for nitrogen
(manure)
• Haber figured out how to
convert N2 into NH3 and
then into NH4
+
of NO3
-
• Commercial fertilizers are
bornFritz Haber
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
21. 1944 Plant Breeding
• Improves yields
• Disease resistance
improvements
• Less day-length sensitive
• Improve sharing of ideas on
plant breeding
C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited
environment.
22. C.5 U.2 The exponential growth pattern occurs in an ideal, unlimited environment.
Examples of exponential population growth
http://www.nature.com/scitable/knowledge/library/an-introduction-to-population-growth-84225544
Throughout the 1800's, hunters
decimated the American
Plains bison populations, and
by 1889, only about one
thousand bison remained.
The US government, along with private
landowners, established protected herds
in the late 1800's and early 1900's. The
herds started small, but with plentiful
resources and few predators, they grew
quickly. The bison population in
northern Yellowstone National Park
increased from 21 bison in 1902 to 250
in only 13 years.
23. C.5 U.3 Population growth slows as a population reaches the carrying
capacity of the environment.
24. 3 Phases:
1. Exponential growth Phase
2. Transitional Phase
3. Plateau Phase
Limited Growth Sigmoid (S-Shaped)Sigmoid (S-Shaped)
C.5 U.3 Population growth slows as a population reaches the carrying
capacity of the environment.
25. 1. Exponential Growth Phase
• Population increases
exponentially.
• Resources are abundant.
• Predators and disease are
rare.
C.5 U.3 Population growth slows as a population reaches the carrying
capacity of the environment.
26. 2. Transitional Phase
• As a result of intra-specific
competition
for food, shelter, nesting
space, etc.,
and the build up of
waste.
• The growth rate slows down.
Birth rates decline and
death rate increases
C.5 U.3 Population growth slows as a population reaches the carrying capacity of the
environment.
27. 3. Plateau Phase
• Natality and mortality are equal so population size is constant.
• When the number of individuals in the population have reached the
maximum which can be supported by the environment.
The number is called the
CARRYING CAPACITY
C.5 U.3 Population growth slows as a population reaches the carrying
capacity of the environment.
28. C.5 U.4 The phases shown in the sigmoid curve can be explained by
relative rates of natality, mortality, immigration and emigration.
Limiting factors are environmental factors that controls
the maximum rate at which a process, e.g. population
growth, can occur.
• build-up of toxic by products
of metabolism
• Injury
• Senescence (death from age
related illness)
29. All examples of competition
for resources
• Injury
• Senescence (death from age
related illness)
• build-up of toxic by products
of metabolism
C.5 U.4 The phases shown in the sigmoid curve can be explained by relative
rates of natality, mortality, immigration and emigration.
30. • build-up of toxic by products
of metabolism
The effect of these limiting
factors increases as the
population increases. These
factors are described as
being density dependent
limiting factors.
• Injury
• Senescence (death from age
related illness)
C.5 U.4 The phases shown in the sigmoid curve can be explained by relative
rates of natality, mortality, immigration and emigration.
31. • build-up of toxic by products
of metabolism
The this limiting factor does
not increases as the
population increases. This
factor is described as being a
density independent limiting
factor.
• Injury
• Senescence (death from age
related illness)
Examples include:
•Climate / weather
•Availability of light (for plants)
•Natural disasters such as volcanic eruptions and fire
C.5 U.4 The phases shown in the sigmoid curve can be explained by relative
rates of natality, mortality, immigration and emigration.
32. C.5 U.5 Limiting factors can be top down or bottom up.
A limiting factor is an environmental selection pressure that limits
population growth. There are two categories of limiting factor:
Top-down factors are pressures
applied by other organisms at higher
trophic levels.
Bottom-up factors are those that
involve resources or lower tropic
levels.
A keystone species exerts top-down influence
on its community by preventing species at
lower trophic levels from monopolizing critical
resources, such as competition for space or
food sources. http://commons.wikimedia.org/wiki/File:Tierpark_Sababurg_Wolf.jpg
http://commons.wikimedia.org/wiki/File:Green_Sea_Turtle_grazing_seagrass.jpg
33. C.5 A.5 Bottom-up control of algal blooms by shortage of nutrients and
top-down control by herbivory.
An algal bloom is a rapid increase or
accumulation in the population of
algae (typically microscopic) in a water
system. http://commons.wikimedia.org/wiki/File:Mar%C3%A9_vermelha.JPG
34. C.5 A.5 Bottom-up control of algal blooms by shortage of nutrients and
top-down control by herbivory.
http://commons.wikimedia.org/wiki/File:Algal_bloom_20040615.jpg
• The water around coral-reef ecosystems is generally nutrient-poor.
• Nutrients in these areas are needed in small amounts are essential for the synthesis
of key proteins and other compounds, e.g. magnesium is needed to make
chlorophyll.
• Algae depend on photosynthesis for nutrition.
• Free-living algae blooms can disrupt coral reef communities by blocking sunlight
and preventing photosynthesis in the symbiotic zooxanthellae. This can cause coral
bleaching (the corals eject the no longer useful zooxanthellae) which leads to the
death of the corals.
http://resources3.news.com.au/images/2011/04/28/1226046/589887-raw-sewerage.jpg
35. With key proteins such as chlorophyll in
short supply the rate of photosynthesis
and hence algal growth is limited.
Nutrients are therefore a bottom-up
limiting factor.
Nutrient enrichment through human activity
(fish farming, fertilizer or sewage outflows
directly or from nearby rivers) can cause
known as eutrophication – algal populations
increase rapidly (blooms) due to the removal of
nutrients as a limiting factor.
36. C.5 S.1 Modelling the growth curve using a simple organism such as
yeast or species of Lemna.
In the absent of equipment using one or more of the following resources to model
population growth:
•Yeast Population Growth lab and simulation by i-Biology
(http://www.slideshare.net/gurustip/population-growth-9457952)
•Bunny population growth by PhET (http://phet.colorado.edu/files/activities/3896/04.02 - CW -
bunny simulation - 2014-07-30 - vdefinis.docx)
Duckweed (Lemna sp.) is a good model organism for measuring sigmoidal
population growth
• Place a small number of plants in a container, e.g. a plastic cup
• Count the number of fronds (leaves) every day until the surface of the container is
covered, i.e. the population has ceased to increase.
• Plot your results – you should obtain a sigmoidal curve
• Your investigation can be extended by considering different independent variables
e.g. nutrient availability and the surface area of the container.
37. Why monitor populationsWhy monitor populations??
• Determine current status of a population
• Determine habitat requirements of a species
• Evaluate effects of management
*Complete “census” of natural populations is often
very difficult!
Population Sampling
C.5 U.1 Sampling techniques are used to estimate population
size.
39. RANDOM SAMPLING
• A sampling procedure that assures that each
element in the population has an equal chance of
being selected
• Sampled population should be representative of
target population
C.5 U.1 Sampling techniques are used to estimate population
size.
Sample Methods
•Quadrat
•Mark-Recapture
•There are MANY more…
40. Quadrat Sampling
• A square frame is placed in
a habitat
• All the individuals in the
quadrat are counted
• The process is repeated
until the sample size is
large enough
C.5 U.1 Sampling techniques are used to estimate population
size.
41. • Useful for small organisms or for organisms that do not
move
C.5 U.1 Sampling techniques are used to estimate population
size.
43. MARK-RECAPTURE (Lincoln Index)
• Capture and mark known number of individuals
• 2nd
round of captures soon after
Time for mixing, but not mortality
• Fraction of marked individuals in recapture sample is
estimate of the proportion of population marked in
first capture
C.5 A.2 Use of the capture-mark-release-recapture method to estimate
the population size of an animal species.
44. Marking methods
• Paint or dye
• Color band
birds
• Unique markings
Large mammals; keep photo record
• Toe clipping
Reptiles, amphibians, rodents
• Radio Collars
• Micro chips
(NPS 2000)
C.5 A.2 Use of the capture-mark-release-recapture method to estimate
the population size of an animal species.
45. Lincoln Index
Using mark-recapture sampling to estimate animal
populations
Population Size P =(# initially marked) x (total 2nd
catch)
(# of marked recaptures)
Or
N1 x N2
N3
C.5 A.2 Use of the capture-mark-release-recapture method to estimate
the population size of an animal species.
48. • You capture and mark 150 fish in a lake. (This must be a
random, representative sample.)
• You release them back into the lake, allowing enough
time for them to remix with the population.
• You trap another 220 fish, of which 25 are recaptures
(i.e., marked from the initial trapping.
• What is your estimate of the total population of fish in
the lake?
Example:
50. Example:
• Use the Lincoln Index to monitor this mountain gorilla
population over time
C.5 A.2 Use of the capture-mark-release-recapture method to estimate
the population size of an animal species.
51. C.5 A.2 Use of the capture-mark-release-recapture method to estimate
the population size of an animal species.
52. Human Effect on the World Fish PopulationHuman Effect on the World Fish Population
• Overexploitation of species affects the loss of
genetic diversity and the loss in the relative
species abundance of both individual and/or groups of
interacting species. Overexploitation may include over
fishing and over harvesting
• Historically, humans have fished the oceans, which
never seemed to pose a problem due to their
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
53. A case study: The Peruvian Anchovy
(Engraulis ringens)
Universidad de La Serena
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
54. The Peruvian Anchovy
• This is a small (12-20cm), short-lived species
maturing in 1 year
• Anchovy live in the surface waters in large shoals
off the coast of Peru and northern Chile
• Here there are cold currents up-welling from the
sea bed bringing nutrients for phytoplankton
• Plankton is at the base of the food chain.
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
55. The Peruvian Anchovy
• The harvest of this fish doubled every year from 1955 to
1961
• Experts estimated the maximum harvestable yield (MSY) at
10 to 11 million tonnes per year
• Through the 1960s the harvest was about this level
• The biggest fishing harvest in the world
• Some of the anchovy were used for human food
• But a lot was ground into fishmeal for animal feed
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
56. The collapse of the anchovy fishery
• In 1972 there was an El Niño event that brought warm tropical water
into the area
• The up-welling stopped,
• the phytoplankton growth decreased
• the anchovy numbers fell and concentrated further south
• The concentrated shoals of anchovy were easy targets for fishing boat
eager to recuperate their harvest
• The political will was not there to impose reduced quotas
• Larger catches were made
• No young fish were entering the population (no recruitment)
• No reproduction was taking place
• The fish stocks collapsed and did not recover
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
57. Population dynamics of fisheries
• A fishery is an area with an associated fish population which is
harvested for its commercial or recreational value. Fisheries
can be wild or farmed.
• Population dynamics describes the ways in which a given
population grows and shrinks over time, as controlled by birth,
death, and emigration or immigration. It is the basis for
understanding changing fishery patterns and issues such as
habitat destruction, predation and optimal harvesting rates.
• The population dynamics of fisheries is used by fisheries
scientists to determine sustainable yields
C.5 A.4 Analysis of the effect of population size, age and reproductive status on sustainable
fishing practices.
58. Sampling
method
Situation in which
the method is used
Usage and limitations
Random sampling Not used. Ineffective as fish are too mobile.
Capture-mark-
release-recapture
Fish are temporarily
stunned with electric
shocks and then
counted
Used in lakes and rivers, but
recapture numbers are too small
to be useful in open waters such
as oceans.
Echo sounders Can be used to
estimate the size of
fish shoals
Only useful for schooling fish
species
Fish catches Age structure of
landed fish can be
used to estimate
population size.
Violators of fishing regulations
designed to control the age of fish
landed often do not report what
they land or they dump the
restricted fish causing a bias in
the estimates.
Estimating Fish populations
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
59. Sampling
method
Situation in which
the method is used
Usage and limitations
Random sampling Not used. Ineffective as fish are too mobile.
Capture-mark-
release-recapture
Fish are temporarily
stunned with electric
shocks and then
counted
Used in lakes and rivers, but
recapture numbers are too small
to be useful in open waters such
as oceans.
Echo sounders Can be used to
estimate the size of
fish shoals
Only useful for schooling fish
species
Fish catches Age structure of
landed fish can be
used to estimate
population size.
Violators of fishing regulations
designed to control the age of fish
landed often do not report what
they land or they dump the
restricted fish causing a bias in
the estimates.
Estimating Fish populations
• Fish are very mobile – they pursue what is
frequently a mobile food supply.
• They often school so are unevenly distributed.
… so how can we count/estimate their numbers?
If we know how big fish population are we can
fish sustainably, but ….
60. Maximum Sustainable Yield (MSY)
Based upon:
1. the harvest rate
2. the recruitment rate of new (young) fish into the
population
• a population can be harvested at the point in their
population growth rate where it is highest (the
exponential phase)
• Harvesting (output) balances recruitment (input)
• Fixed fishing quotas will produce a constant
harvesting rate (i.e. a constant number of individuals
fished in a given period of time)
C.5 A.4 Analysis of the effect of population size, age and reproductive status on
sustainable fishing practices.
61. Maximum Sustainable Yield (MSY)
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
62. Maximum Sustainable Yield
• The Largest possible catch without adversely affecting
the ability of the population to recover.
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
63. Problems with MSY
Age structure: If all the age groups are harvested recruitment
of young fish into the reproductive group will be reduced.
The answer is to use a net with a big enough mesh size that
lets the young fish escape
Age and sustainable fishing
• If a population is growing, then the relative number of
younger fish will be higher (there are many potential
breeding fish for the future).
• If a population is in decline, then the proportion of older fish
will be higher (older fish have a higher mortality and are
unlikely to be as productive in breeding).
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
64. Problems with MSY
Limiting factors: If the limiting factors in the environment
change so does the population growth rate
• Limiting factors set the carrying capacity (K) of an
environment
• Increasing limiting factors will cause K to drop
• Fixed quotas cannot cope with this
• Data: For MSY to work accurate data in fish
populations is needed (population size, age structure,
recruitment rates)
• Usually these are not well known
C.5 A.4 Analysis of the effect of population size, age and reproductive
status on sustainable fishing practices.
65. What is required?
• Nets with bigger mesh size
• Regulated fishing methods
• More data on fish populations (e.g. by fish tagging
investigations – mark and recapture)
• Constant monitoring to observe changes in environmental
factors (e.g.El Niño events
• Policing of fishing industry – respect of quotas
• International agreements
• Greater exploitation of fish farming
• But this is not without its own problems (space, diseases
and pollution are all associated with intensive fish culture)
66. C.1.A1 Distribution of one animal and one plant species to illustrate limits of tolerance and zones of
stress.
Shelford's law of tolerance is a useful tool to understand the relative abundance of a species
and hence predict community structure. It plots the range of a biotic or abiotic factor that is
tolerated by a species,. Because their is variability but within a population the limits of
tolerance and where the zones of stress start is not always easy to measure.
http://www.anselm.edu/homepage/bpenney/teaching/BI320/elements/Krohne_Shelfords.jpg
