7 billion and growing
How can humans cause population
decline in other species?
How can humans cause population decline in other species?
“As dead as a dodo”
humans
Mauritius,
dogs
pigs
cats
rats
nests,
forests
Four ways humans can cause
population decline are:
•
•
•
•
Habitat ……………………………… (e.g. endangered panda)
Introducing new ……………………… (e.g. extinction of dodo)
Over………….. (decline in rhinos)
……………………… change (decline in polar bears)
How can humans cause population
growth in other species?
How can humans cause population growth in other species?
Four ways humans cause population
growth in other species:
Improve conditions (
)
Reduce pressure from predators (
Reduce competition (
Introduce animals to new areas (
)
)
)
Humans are k strategists.
Fish are r strategists.
Fish? Human?
Long life vs short life
Slower growth vs rapid growth
Mature late vs mature early
Many small offspring vs few large offspring
Little parental care vs lots of parental care
High investment in individual offspring vs little investment in individual
offspring
Predators vs prey
Lower trophic level vs higher trophic level
Pioneers and colonisers vs later stages of succession
Population may crash vs live close to carrying capacity
Adapted to unstable environment vs adapted to stable environment
r strategists
k strategists
flour beetles
annual plants
trees
bacteria
albatrosses
Which are r strategists?
Which are k strategists?
For one example of each explain why.
humans
Survivorship curves: I II III
A: Almost all individuals survive for their potential lifespan and then die almost
simultaneously
B: Most individuals die at a very young age but those that do survive are likely to
survive for a very long time
Answer:
1. Which of the following is a characteristic of Kselected organisms?
A. They are typical of pioneer communities.
B.Usually a very high percentage of young die
during the early part of their life cycle.
C.Sexual maturity is reached early in the
lifespan.
D. They usually have a high degree of parental
care of young.
Answer:
2. Which statement most correctly describes Kstrategist organisms?
A. They reach adulthood quickly and have
many young.
B.They reach adulthood slowly and have many
young.
C.They reach adulthood quickly and have few
young.
D. They reach adulthood slowly and have few
young.
Answer:
3. Which of the following is characteristic of rselected organisms?
A. They are typical of pioneer communities.
B.Usually a high proportion of the young
survive to adulthood.
C.Sexual maturity is reached late in the
lifespan.
D. They usually have a high degree of parental
care of their young.
4. The graph below shows the number of
individual organisms surviving from an initial
cohort of 1000, plotted against time. (A cohort is
a group of organisms in a population that are born
or hatch at about the same time.) Which line on
the graph is most likely to represent a Kstrategist?
A.I
B. II
C. III
D.IV
Answer:
5. I species reproduce and disperse rapidly and
unfavourable environmental conditions can cause
such populations to II
Which of the following provides the correct words
to be inserted in the sentence above?
Answer:
I
II
A.
r-strategist
increase
B.
K-strategist
crash
C.
K-strategist
increase
D.
r-strategist
crash
Answer:
6. An r-strategist generally
A. gives considerable parental care to its
offspring.
B. is small and short-lived.
C. lives in a stable environment.
D. produces small numbers of offspring.
Answer:
7. Which of the following is a typical
characteristic of a K-strategist?
A. Little or no parental care and protection
of offspring
B. Low ability to compete
C. Reproduce late in life
D. Reproduce and disperse rapidly when
conditions are favourable
Answer:
8. Which statement about K-strategists is
correct?
A. They are less adaptable than r-strategists.
B. They have high genetic diversity.
C. They exhibit fast rates of evolution.
D. They live in a rapidly changing
environment.
Answer:
9. Oysters release millions of eggs each time
they breed, but most of their offspring die
before reaching adulthood.
This is an example of
A. an r-strategist organism.
B. an organism threatened by extinction.
C. a K-strategist organism.
D. an organism typical of a climax community.
10. Lines I, II and III are survivorship curves for three different
populations in an ecosystem. Which row best describes the nature of
the three populations?
Answer:
A.
B.
C.
D.
r-strategists
K-strategists
Intermediate strategists
III
I
III
I
II
III
I
II
I
II
II
III
Answers
1
2
3
4
5
6
7
8
9
10
What factors are going to stop the human
population from growing?
The world is fast-reaching its carrying capacity.
(the maximum number of organisms that an area or ecosystem can sustainable
support over a long period of time)
Evaluate the use of models in population prediction
+ or –
Many factors affect birth rate
Many factors affect death rate
Hard to predict how these
factors will change
Predictions are accurate within
some range
Need something to use for
planning purposes
What single factor affected the decline in China’s
population growth rate?
What factors will stop animal and plant
populations from growing?
These are called limiting factors
Tolerance range
Range of intolerance
Optimum range
Stress
Absent
Carrying capacity
(1) is the maximum number of organisms that an area or ecosystem
can sustainable support over a long period of time.
Every species has a (2) for any environmental factor.
There is an (3) within which any species can thrive.
Beyond this a species will suffer (4)
Above and below the tolerance threshold is the (5) where the
species will be (6)
Explain the concepts of limiting factors and carrying
capacity in the context of population growth.
Malthus
Boserup
Who was he?
Who was she?
When did he live?
When did she live?
What was his profession?
What was her profession?
What did he predict?
What did she predict?
What was his limiting factor?
How did she think we would overcome this
limiting factor?
List 10 ways we have been able to
increase food supply since Malthus’s
time.
What did her studies show about change in
farming techniques?
Describe and explain S- and J- population curves
Label the s curve and the j curve.
What are the stages in the typical s curve?
DENSITY-DEPENDENT AND
DENSITY-INDEPENDENT FACTORS
These are factors that control the
population size.
density dependent?
density-independent?
disease
density dependent?
density-independent?
tsunamis
parasitism
volcanic eruptions
negative
positive
density dependent
birth
death
density-independent
biotic
abiotic
Some limiting factors are related to how dense the
population is. Some aren’t.
…………………………………………………….. factors will control a
population size if there is a high population density.
They lower the …………………….. rate or raise the
……………………….. rate as the population grows in size.
Density dependent factors cause …………………………………….
feedback to occur e.g.
……………………………………………….. will control a population
size whether there is a high population density or not.
Density independent factors are usually
……………………………
e.g.
Density-dependent limiting factors
Internal factors:
Act within a
species
Limited breeding areas?
Predation
Disease
Limited food supply
External factors:
Act between
species
Think: how do predator-prey relationships control
the population size of both the predator and the
prey?
How do limited breeding areas control the
population size and leads to a better gene pool?
Density-dependent limiting factors
Internal factors:
Act within a
species
External factors:
Act between
species
Limited breeding areas
Limited food supply
Predation
Disease
Explain how predator-prey relationships control
the population size of both the predator and the
prey.
Explain how limited breeding areas controls the
population size and leads to a better gene pool.
1. What are density dependent factors?
2. What are density independent factors?
3. What are internal and external factors?
How do density-dependent and densityindependent factors, and internal and external
factors, regulate populations?