IB Environmental Systems and Societies

1. Topic 4
Conservation and Biodiversity
4.1 Biodiversity in Ecosystems

2. Biodiversity
• Coined by Edward Wilson in the 1980s
• It is the number and relative abundance of
species in a defined area
• It can be measured in terms of:
– 1. Species diversity
– 2. Habitat diversity
– 3. Genetic diversity

3. 1. Species Diversity
• The variety of species per unit area
• This is the number of species present and
their relative abundance
• Areas of high species diversity are usually
those undisturbed by humans

4. 2. Habitat Diversity
• The range of different habitats in an ecosystem
– Rainforest has a high habitat diversity
– Desert has a low habitat diversity

5. 3. Genetic Diversity
• The range of genetic material present in a
gene pool or population of a species

6. Plate Tectonics
• First suggested by geologist Alfred Wegener in
1912
• It refers to the movement of parts of the Earth’s
crust
• This led to populations of the same species
becoming isolated (over millions of years)
• Reproductive isolation under different conditions
provided a mechanism for speciation (in this case
allopatric)
• It explains why there are related species in
different parts of the world

7. 300 – 200 million years ago
Pangea

9. 200 – 180 million years ago
Lauraisia
Gondwanaland

10. How does plate movement influence
speciation?
• May produce barriers
– Mountain ranges
– Rift valleys
– Oceans
• Movement of land masses apart can isolate species
• Land bridges may form and allow new waves of colonisation
• Movement of plates through new climatic zones creates new
habitats
• Subduction of plates sometimes destroys existing habitats

11. Evolution
Charles Darwin (1809-1882)

12. Evolution
Evolution is the slow, continual change of
organisms over a very long time. All living things
on the Earth have developed from the first
simple life forms that arrived 3,000,000,000
years ago.
One of the effects of evolution is that species will become better
adapted to their environment. If these species don’t adapt they
may become extinct due to being unable to deal with any of these
factors…
1) Increased competition
2) Changes in the environment
3) New diseases
4) New predators

13. Evolution
My key observations:
1) All living things produce more offspring
than survive to adulthood
2) In spite of this, population sizes remain
roughly constant
3) Variation exists among species
4) Characteristics can be passed on from
one generation to the next.
These observations led me to the
conclusion that species evolve over a
along period of time by a mechanism
called “Natural Selection”. The main
evidence for this is from fossil records.

14. Evolution
Mutations are changes in the structure of the DNA molecule. They can be passed on
to daughter cells through cell division. They will result in the wrong proteins being
produced.
Mutations can be caused by:
- Ionising radiation (UV, X-rays etc.)
- Radioactive substances
- Certain chemicals
Effects:
- Mostly harmful
- Causes death or abnormality in reproductive cells
- Causes cancer in body cells
- Some CAN be neutral or even beneficial (e.g. the peppered moth)

15. Natural Selection
1) Each species shows variation:
2) There is competition within each
species for food, living space, water,
mates etc.
4) These survivors will pass on their better
genes to their offspring who will also show
this beneficial variation.
Yum
3) The “better adapted” members of
these species are more likely to survive
– “Survival of the Fittest”
Get off
my land
Gutted!

16. A smaller example…
Consider the four steps of natural selection in the example of some
bacteria that have become resistant to penicillin (an antibiotic):
1) Variation – some strains of bacteria are
resistant and some aren’t.
2) Competition – The non-resistant bacteria
are killed by the penicillin.
3) Survival of the fittest – the resistant
bacteria survive.
4) Passing on of genes – the resistant
bacteria reproduce and pass on their
adaptations to their offspring.
Bacteria
Penicillin

17. Evolution is usually divergent (sometimes refered to as adaptive radiation). However,
occasionally unrelated species develop similar characteristics due to similar selection
pressures. We call this convergent evolution.

18. Examples of Convergent Evolution

19. Divergent Evolution
• Also called “adaptive radiation”

20. Ecosystem Stability and Disturbance
• After a disturbance, new habitat is recolonised:
– By swimming or floating
– By flying (birds, insects, seeds)
– By walking or ‘hitch-hiking’ on other animals

21. Ecosystem Stability and Disturbance
• Jump Dispersal
– Long distances travelled by one or few individuals over a
very short timescale
• Diffusion
– Slow spread of a population from the edge of a
disturbance into new habitat
• Secular migration
– Very slow spread (over thousands or millions of years) that
may involve species undergoing speciation as they move

22. Disturbance
• 3 factors determine how quickly an ecosystem
can recover from a disturbance:
– Inertia – resistance to alteration
– Resiliance – ability to recover
– Diversity – number and proportions of species

23. Disturbance
• Tropical rainforest
– High diversity
– High inertia
– Low resiliance (takes a long time to recover)
• Grassland
– Low diversity
– Low inertia
– High resiliance
Complex ecosystem therefore has
many ways to respond to
disturbances. However, soils thin and
low in nutrients, and eaily washed
away after disturbance
Fairly simple ecosystem. Thick soils
with lots of nutrients stored in them.
Recover fairly quickly after
disturbance

24. Succession
1. Pioneer Species colonise bare rock
2. Growth of these species cause changes in the
environment, soil is created
3. New species colonise soil and replace pioneers
4. Growth of root systems stabalise soil
5. Animals begin to colonise
6. A climax community is created
7. New disturbances result in new waves of succession
Primary
Succession
Secondary
Succession
Note that it is communities that succeed each other, not simply individual species
Each new community is called a sere. The final stable sere is called the climax community

25. Questions
1. Define species diversity, genetic diversity and habitat
diversity
2. Describe natural selection and artificial selection
3. List 3 different causes of reproductive isolation
4. Describe allopatric speciation and sympatric speciation?
5. Outline the movement of tectonic plates and how it has
contributed to species distribution

26. Questions
1. Give one example of how an ecosystem’s
ability to recover from a disturbance depends
on resiliance, diversity and inertia
2. In what ways does the complexity of an
ecosystem provide stability?
3. Outline the difference between primary and
secondary succession