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

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

Mass Extinctions

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

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

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)

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

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

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

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

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

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