1. Unit 3 3.7- Mass Extinctions and Biodiversity
Higher Biology
Unit 3
3.7- Mass Extinctions and Biodiversity

2. Extinction
When an organism is classed as extinct there are no living members of that species left
Extinction is a natural process where organisms that are less suited to an environment die out
Throughout the history of earth there have been several mass extinction events

3. Mass Extinctions

4. Mass Extinction
Mass extinctions are closely related to changes in global climate
These changes in climate result in different selection pressures being places on organisms
Only the organisms best suited to the new conditions will survive and reproduce
Evidence of mass extinctions comes in the form of fossil records

5. Impact on Biodiversity
Immediately following a mass extinction biodiversity may be reduced
Over time speciation will occur and biodiversity will increase as new species emerge
For examples, the diverse number of mammalian species that now exist evolved from a small number of common ancestors

6. Extinction Rate
Extinction rates can be difficult to measure accurately so are very approximate
Human impacts on the environment are increasing the rate of extinction across many species
Fossil records show that the arrival of Homo sapiens in a new area was quickly followed by extinction of the largest animals (megafauna)

7. Ecosystem Degradation
Humans are changing the environment to make space and resources available for the increasing human population
Over hunting and habitat destruction have resulted in the loss of hundreds of species of birds and mammals

9. Measuring Biodiversity
When looking at biodiversity there is no single measure used to compare the differences between living things
Biodiversity measures are useful in helping us to monitor the changes in populations and ecosysystems
There are 3 measurable components of biodiversity

10. Genetic Diversity
Genetic diversity results from the variation shown by the number and frequency of alleles possessed within a population
By measuring the number and frequency and alleles we can observe loss in genetic variation within a population
This may be a problem for a species as the loss of certain alleles may limit their ability to adapt to changing conditions in the future

11. Species Diversity
When measuring the species diversity of an ecosystem 2 measures are taken into account
Species Richness- the number of different species present
Relative abundance- the proportion of each species in the ecosystem
Ecosystems can share the same species richness but differ in their relative abundance of each species

12. Ecosystem Diversity
Ecosystem diversity refers to the number of distinct ecosystems present in a defined area
Within a geographical area there can exist a number of different ecosystems

13. Island Biogeography
Island biogeography is the study of the factors that affect the distribution and diversity of species on islands
Islands can refer to:
A true island- a land mass surrounded by water permanently
A habitat island- an area surrounded by a different ecosystem that cannot be colonised by the island species
The more isolated an island the lower the diversity found among its species
The smaller the surface area of the island the lower the biodiversity