3.7 Mass extinction and Biodiversity Flashcards
What is biodiversity?
biodiversity is the term used to describe the millions of different species of animals, plants and microorganisms on earth
What is biodiversity important for?
providing different sources of food
supplying sources of medicines
stability of ecosystems
providing economic value
DONT FORGET
biodiversity is the variety of living things on earth
What is extinction?
living species naturally become extinct and are replaced by others
What is mass extinction?
a mass extinction is a rapid decrease in the number of species on Earth
25-70% of all species may cease to exist over a period of tens of thousands of years e.g. the extinction of the dinosaurs
when organisms die their remains may be preserved as fossils providing a record of their existence
fossil evidence has shown that several mass extinction events have occurred in the past and that the holocene extinction which began 11500 years ago is still ongoing
What is speciation?
a mass extinction leaves may unfilled niches and the surviving organisms may take advantage of these
new species evolve from a common ancestor to fill these empty niches as happened when mammals diversified into the empty niches occupied by dinosaurs
What follows a mass extinction?
a period of recovery as biodiversity is lowly regained
What is the background extinction rate a measure of?
measure of how often extinctions happen naturally without the interventions of humans
a broad estimate of the extinction rate can be calculated by measuring the number of species that become extinct over a certain period of time
this is easier for large, visible species such as mammals, but very difficult for less visible species such as bacteria, fungi and insects
What are megafauna?
species of very animals
e.g. wooly mammoth
What contributes to these mass extinctions?
climate changes, as well as hunting by humans, are likely to contribute to these extinctions
what made it impossible to recover?
their slow reproduction
Why is the current rate of species extinction is much greater than the background rate?
due to the rapidly increasing rate of ecosystem degradation by humans, which endangers the survival of many species
What are the main causes of ecosystem degradation by humans?
deforestation - cutting down forests to make way for agriculture
pollution of air, water and land
over exploitation of resources for example overfishing and overhunting
destruction of habitats - the removal of hedgerows
what are the role of humans in the extinction of polar bears?
activities such as deforestation and fossil fuel burning which lead to global warming
what are the role of humans in the extinction of siberian tiger?
low genetic diversity and poaching by humans
what are the role of humans in the extinction of black rhinoceros?
habitat destruction and poaching by humans
What are the three elements which together can provide a measure of biodiversity?
genetic diversity
species diversity
ecosystem diversity
What is genetic diversity?
the number and frequency of alleles in a population of a species of animal or plant are estimated
the higher the number and frequency of alleles, the greater the biodiversity
What happens when a particularly population dies out?
then alleles are lost and genetic diversity decreases
why is lack of genetic diversity an issue?
because if environmental conditions change, the species may not be able to adapt
e.g. a lack of genetic diversity lead to the irish potato famine since only two varieties of potatoes were planted and neither was resistant to the fungus responsible for the blight
What is species diversity?
the number of different species of living organism in an ecosystem are estimated using sampling techniques
the relative abundance of a species of how many individuals there are compared to other species in an ecosystem can also be estimated in this way
TOPTIP
sampling techniques include quadrats line transect pitfall traps tree beating sweep netting
What is ecosystem diversity?
a record is made of the number of different types of ecosystem that exist within an area, the higher the ecosystem diversity for that region.
TOPTIP
different types of ecosystem include: woodland soil fresh water marine beach moorland mountain tree hedge grassland
What is the biodiversity in habitats related to?
related to the area of the habitat
Biodiversity drops more quickly than..?
than the reduction of habitat size
What does this mean when habitats are fragmented?
the impact is disproportionately high
How are small fragments known as habitat islands created?
the breaking of tracts of rainforest by logging roads or by the creation of patches of agricultural land decreases the overall biodiversity by creating small fragments
What does the species diversity of a habitat island depends on what?
on its area and the degree of isolation from other habitats
DONT FORGET
high species diversity results in a stable ecosystem with complex food webs while low species diversity gives an unstable ecosystem with simple food webs: one small change could cause many species to die
