Plan – Week 3
• Test on 5.1 – Today or Tuesday…
• Test on 5.2 (Greenhouse Effect, Carbon Cycle
and Climate Change) : Friday
• In between….5.3 and Topic G.3:
Population Ecology and Invasive Species
5.3 Population Ecology
What you need to know about
populations (Topic 5.3, SL and HL)
• Key Factors which determine population
size
• You must know how to draw, and
interpret, a classical population growth
curve
• Factors which set limits to population
increase
What ELSE you need to know about
populations (Topic G, SL and HL)
• You must understand the impacts of alien
species
• You must be able to give three examples
of alien species in ecosystems
• You must outline one example of
biological control of an invasive species
What ELSE you need to know about
populations (Topic G, HL, NEXT YEAR)
• You must understand and distinguish
between r-strategies and K-strategies
• You must understand environmental
conditions that favour r- or K-strategies
• You must understand a method to
estimate population size (catch and
release)
Let’s start simple…
WHAT IS A POPULATION?...
Human Population
• At what point in human history did the
population reach 1 billion people?
• It took all of human history up to the early
1800s for world population to reach 1 billion
people, and until 1960 to reach 3 billion.
Today, the world gains 1 billion people every
11 years.
Let’s Review: What is a population?
(5.1.1)
A group of organisms of one species that
interbreed and live in the same place at the
same time
Key Characteristics of Populations 1:
Geographic Distribution
Characteristics of Populations 2:
Population density
The number of individuals per unit area
Population Density
•
Can vary tremendously depending on the
species and its ecosystem
A field of sunflowers
A flock of birds
A few saguro cactus
Turtles grouped to sun
Population Density
What are some benefits of living close together
or in a clumped population?
1. Help finding food
2. Protection from predators
or wind
3. Easier to find species
Population Density
What are some drawbacks (negatives) of living
in a clumped population?
1. Crowded living areas
2. Battles over food/shelter
3. Easier for disease to spread
Characteristics of Populations:
Evaluating Growth Rate
The amount by which a population’s size
changes in a given time
Let’s imagine a brand new population
of….
• Let’s think about how it changes over time….
• How does it arrive in its new habitat?
• Which factors will affect population size over
time?
• You have two minutes…
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5.3.1 What are the four factors that
affect populations?
What affects population size?
Number of births (natality)
Number of deaths (mortality)
Number of individuals
that enter (immigration)
or leave (emigration)
Population Growth
• Migration- periodic movements of
populations away from and back to their
place of origin
(not what we are talking about here)
• Irregular movements of some
individuals out of an area, into a new
area, with no return - affects
population size
• Immigration – movement of individuals into
an area
 Population increases in size
• Emigration – movement of individuals
out of an area
 Population decreases in size
Population Growth
• Why would an animal immigrate to or emigrate
from a population?
• Competitive pressures on some individuals
– To find food, better living conditions, or a mate
Evaluating population growth…
doing the mathematics…
If a population has
unlimited food and space
and is protected from
predators and disease,
what will happen to the
size of the population?
What would population growth looks like on a graph when an
population colonizes a new habitat?
Draw a graph and explain the shape.
Work with a partner.
You have five minutes.
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It will increase exponentially!
Under ideal conditions
with unlimited
resources
and no predation, a
population will grow
exponentially
Some formulae (you don’t need to
know these!)
(Reference:
http://www.nature.com/scitable/knowledge/libr
ary/how-populations-grow-the-exponentialand-logistic-13240157
• Exponential growth:
• Logistic Growth (Transitional phase):
Exponential Growth
• Example: Bacteria  reproduce in ~20 minutes by
splitting in half
– 1 bacteria after 20 min = 2 bacteria
– 2 bacteria after 40 min = 4 bacteria
– 4 bacteria after 60 min = 8 bacteria
– In 180 min (3 hours) = 512 bacteria
– In one day = 4,720,000,000,000,000,000,000 bacteria
Exponential Growth
• Exponential growth occurs when the
individuals in a population reproduce at a
constant rate
This is what a graph
– Creates a “J” shaped
curve
– Under ideal conditions
with unlimited resources
and no predation, a
population will grow
exponentially
of bacterial growth
would look like if the
growth went
unchecked
Can exponential growth continue for
ever?
Write down the factors that set
limits to population size
You have two minutes…
What are factors that set limits to
population size?
•
•
•
•
Competition for resources
Build up of toxic by-products of metabolism
Increased predation
Incidence of disease.
Birth and Death Rates
• Affected by
– Biotic factors
• Disease, predators, food, competitors
– Abiotic factors
• Rainfall, temperature, light, pollution
– Can be density dependent or density
independent
– Can be extrinsic or intrinsic
Limits to Growth
• Medium Galapagos finch
• Droughts (fewer seeds)
– Death rate increases
– Birth rate decreases
• High rainfall (more seeds
and caterpillars)
– Death rate decreases
– Birth rate increases
Logistic (Transitional) Growth Phase
• Do bacteria cover the planet?
• Exponential growth does not continue in
populations very long.
• As resources become less available, the
growth of a population slows or stops
• What might cause population growth to stop
or slow down?
– Predators, loss of habitat, disease, competition
for resources: less food, less space etc.
Logistic Growth (Transitional Phase)
• Logistic growth (transition phase)
occurs when
population growth slows or stops
following a period of exponential
growth
– Creates an “S” shaped curve
• Population growth may slow or stop
for a number of reasons:
– Birthrate ↓
death rate ↑
immigration ↓ emigration ↑
• At some point, the growth of a
population will level off (stabilise,
plateau phase)
Comparing Exponential and Logistic
Growth
Carrying Capacity
Carrying Capacity (K)
• The maximum number of individuals that a
particular habitat can support
The classical ‘Sigmoid’ Population
growth curve
Most plant and animal
populations follow this
type of
growth
What is happening in this population
graph?
Finches & Rainfall
Some formulae (you don’t need to
know these!)
(Reference:
http://www.nature.com/scitable/knowledge/libr
ary/how-populations-grow-the-exponentialand-logistic-13240157
• Exponential growth:
• Logistic Growth (Transitional phase):
Alien Species
What is an alien species?
• An alien species is one
which arrives in a nonnative habitat, usually as a
result of intentional or
accidental human activity
• Often, they are not well
adapted to their new
habitat and don’t survive
(too far outside their ‘niche’
• MANY have been hugely
successful in their new
habitat, causing huge
ecological and economic
damage
The Classic Examples:
• Zebra Mussels in American
Great Lakes
• Cane Toads in Australia
• Rabbits in Australia
• Japanese Knotweed in
Europe
• Bamboo in Europe
There are literally hundreds of
thousands more…
Example of an Alien Species: The Cane
Toad
• http://www.youtube.com/watch?v=gYUHnf7U
y1k&feature=player_embedded
• http://www.youtube.com/watch?v=8q77CIQo
dVw
Homework (2)
http://www.issg.org/database/
welcome/
• The Global Invasive Species
DataBase
• Use the database to build a
factsheet about one
invasive species, EITHER
from your home country,
OR Switzerland
You must provide:
• Common name and
Binomial nomenclature
• Native and introduced
habitat range
• Introductory
pathway/vectors
• Local dispersal methods
• Impacts on local ecosystem
and environment
• Management strategies
• Images
What would population growth looks like on a graph when an
population colonizes a new habitat?
Draw a graph and explain the shape.
Work with a partner.
You have five minutes.
5.3.2, 5.3.3
A
B
A
5.3.2, 5.3.3
K = carrying
capacity
A
r = rate of
reproduction
N0 = starting
population
B
A
5.3.1 What are the four factors that
affect populations?
Population Growth
Population Stability
Population Decline
What would population growth looks like on a graph when an
population colonizes a new habitat?
Make the shape of a Sigmoid graph
with your hand
in the air.
Homework (1): Zebra Mussel
Webquest (Population Study)
http://ats.doit.wisc.edu/biology/ec/pd/t1_a1_b.
htm
5.3.1 What are the four factors that
affect populations?
Population Growth
Population Stability
Population Decline
What would population growth looks like on a graph when an
population colonizes a new habitat?
Make the shape of a Sigmoid graph
with your hand
in the air.