Topic 4: Conservation and biodiversity
4.1 Biodiversity in ecosystems (3 lessons)
By the end of this topic you will be able to:
4.1.1 Define the terms biodiversity, genetic diversity, species diversity and habitat diversity.
4.1.2 Outline the mechanism of natural selection as a possible driving force for speciation.
4.1.3 State that isolation can lead to different species being produced that are unable to interbreed to
yield fertile offspring.
4.1.4 Explain how plate activity has influenced evolution an d biodiversity.
4.1.5 Explain the relationships among ecosystem stability, diversity, succession and habitat.
Biodiversity
Genetic diversity,
Species diversity
Habitat diversity.
Model:
Biodiversity comes from the phrase biological diversity.
It is now used to mean the variety of life on Earth.
‘Bio’ makes it clear that we mean the biological parts of
the ecosystem and ‘diversity’ is a measure of both the
number of species in an area and their relative
abundance (how many of each species there are).
Biodiversity can be used to evaluate both the
complexity of an area and how healthy that area is.
Biodiversity is measured in three ways: species
diversity, habitat diversity and genetic diversity.
Species diversity is the variety or number of
different species in a unit of area e.g. a km2.
It includes the number of species present and
their abundance (how many of each one there
are).
The higher the species diversity of a community,
the greater the complexity.
Areas of high species diversity are also more
likely to be undisturbed by people e.g. primary
rainforest).
*Species richness means only the number of
species.
Genetic diversity means the range of genetic material present in a gene pool or in a population of a species.
Genes are sections of DNA found in the nucleus of every cell and they are the instructions from which a
species is produced.
Gene pool refers to all the different genes found in all the individuals of the species in that area.
A large gene pool leads to a high genetic diversity and a small gene pool leads to a low genetic diversity.
Gene pool can refer to the diversity of genes in all species within an area.
Habitat diversity means the range of different habitats in an ecosystem.
Habitat diversity is often connected to the variety of ecological niches.
So, for example, a woodland has many different niches, such as a rivers, trees and soil, and so it has a
high habitat diversity. A desert has few habitats, maybe sand and occasional vegetation, and so has a low
habitat diversity.
Use biodiversity to model jigsaw activity: someone explains what biodiversity means. I can only draw the
meanings I get.
JIGSAW
ACTIVITY
Each table of students is given one of the three definitions. They make sure as a table that they understand
their definition. Move around room to get information. They have to draw the meanings for the two they
have not got, and explain their one to the other two tables.Come back to their table to pool information and
use it to write definitions for the two terms.
Check understanding
1. Are species with a high or a low genetic diversity more prone to extinction and why? Think about what
would happen if the environment changes. Think about cheetahs with a low genetic diversity.
2. How could we increase the genetic diversity of an area?
3. How could we increase habitat diversity?
4. How could we increase species diversity?
5. Put into context: As an environmentalist, which of the three methods of increasing biodiversity will be the
most successful and why?
6. Practical: How could we measure biodiversity in any given area?
7. How do we measure it?
SIMPSON’S DIVERSITY INDEX(D)
D = diversity index
N = total number of organisms of all species found
D=
n = number of individuals of a particular species
N (N – 1)
∑ n (n-1)
∑ = sum of
Species
woodrush
Holly
Bramble
Yorkshire fog
sedge
Total (N)
D=
(n)
2
8
1
1
3
15
n(n-1)
2
56
N (N – 1)
∑ n (n-1)
So N =
A high D value would mean…
a stable and ancient site
A low D value would mean…
pollution, recent colonisation or agricultural management
Why?
How would a cumulative species count work?
When would you know how to stop counting quadrats?
Graph
Measures of diversity are relative, not absolute. Why?
True or false: You can compare between communities containing the same type of organism and in the same ecosystem
True or false: You can compare between different types of community and different ecosystems.
Communities with individuals evenly distributed between different species are said to have high evenness and have high
diversity. This is because many species can co-exist in the many available niches within a complex ecosystem.
Communities with one dominant species have a low diversity which shows a poorer ecosystem not able to support as many
types of organism.
Measures of diversity in communities with few species can be unreliable as relative abundance between species can
misrepresent true patterns.
BIG UNDERSTANDING
Why is biodiversity important?
IB exam question
1a) Identify, giving reasons, two actions which will promote species diversity.
(2)
1b) Explain why species diversity is considered to be an advantage to an ecosystem.
(3)
Natural selection(as a possible driving force for speciation)
Speciation - isolation (geographical or reproductive) of populations.
fitness
State that isolation can lead to different species being produced that are unable to interbreed to yield fertile
offspring.Isolation of populations, behavioural differences that preclude reproduction and the inability to produce fertile
offspring (leading to speciation)should all be examined, with examples.
Plate activity
The consequences of plate tectonics on speciation should be understood (that is, the separation of gene pools, formation of
physical barriers and land bridges) together with the implications these consequences have for evolution. The role of plate
activity in generating new and diverse habitats, thus promoting biodiversity, should also be considered. Detailed
understanding of the mechanism of plate tectonics is not required.
Ecosystem stability, diversity, succession and habitat
Consider how:
• diversity changes through succession
• greater habitat diversity leads to greater species and genetic diversity
• a complex ecosystem, with its variety of nutrient and energy pathways, provides stability
• human activities modify succession, for example, logging, grazing, burning
• human activities often simplify ecosystems ,rendering them unstable, for example, North America wheat farming versus tall
grass prairie
• an ecosystem’s capacity to survive change may depend on diversity, resilience and