Biodiversity and Extinction
Biodiversity and Extinction (Human Biology)
- Created by: Katrina
- Created on: 14-05-12 16:31
Biodiversity
the number of species on the planet
keystone species-a species upon another species depend e.g. bees for plants
human activity has negative effects on the environment leading to a biodiversity crisis
ecosystems e.g. rainforests and coral reefs have the most diverse habitats and most concentrated number of species on Earth
ecosystems e.g. deserts have less biodiversity
rainforests are being destroyed to make room for and support the human population
Extinction
loss of species
local extinction-when a species are extinct within a small area. Too many can lead to total extinction
living dead extinction-when the population is so low they may as well be extinct-can lead to genetic weakness
rate of extinction-how fast species loss is occurring
normal background rate=one extinction per million years
massive destruction of habitats due to deforestation, urbanisation, agriculture, pollution (global/ocean warming), mining
coral reefs are the habitat of 1/3 the planet's marin =e fish and 1/2 could be lost to the next 20 years
important to prevent extinction so we have ecological balance
Endangered Species
human activity is the main cause
endangered species-one whose numbers are reaching a critical point leading to possible extinction of the species e.g. golden lion, tamarin, snow leopard, giant panda
main causes: loss of habitat; overhunting by humans; competition from introduced species; deforestation; pollution; drainage of water
benefits of other species to humans: medicine, food, fibres, transport
extinction of plant species before investigation their medicinal properties may prove to be an incalculable loss
there is great need for species conservation
Evolution
the process by which new species are formed from pre-existing ones over long periods of time
first put forward by Charles Darwin
he gathered geological and fossil evidence to support the idea that life changes with time
suggested natural selection is the force that causes changes in populations
Adaptive Radiation
1882-Darwin travelled to Galapagos islands to observe, classify and describe the indigenous (native to that area) plants and animals including finches
fossils he collected showed different changes various life forms had gone through
suggested 1 ancestral species of bird must have been carried by the wind from the mainland
no other bird species occupied the islands so food variety was available
individial finches differed from one island to the next-main difference beak size and shape which related to the type of food eaten e.g. nuts, berries, nectar, insects
charateristics suited to the environments were inherited by the offspring
Darwin suggested the finches developed from one common ancestor and the beak type developed over time-had become specialised to feed on a particular food source
an example of adaptive radiation
Natural Selection
in any population there is variation
individuals have the potential to produce a large number of offspring
there is a struggle for survival and only the strongest, fittests individuals who are best suited to their environment survive
the fittests individuals survive and reproduce offspring who have the same favourable characteristics
over time a group of individuals that once belonged to a species may give rise to 2 groups that are sufficiently different to now form a separate species
Species
a group of organisms which share a large number of common characteristics and cab breed to form viable, fertile offspring
if the individuals over time have become so different that they can no longer breed, they are considered to be different species
Gradual Change/Sudden Leaps
evidence suggests the Earth's climate has changed in the past which has affected life on the planet
plants and animals from the past can be strudied from their fossil records (palaeontology)
if extinct animals and plants are arranged in geological sequence, we can see how one group may have evolved into another
intermediate forms should be found in successive rock layers, between one fossil species and the next, but these are surprisingly rare
What do Creationists Believe?
American scientists Eldrige and Gould suggest species arise rapidly (within a few thousand years) and remain unchanged for several million years before evolving again
evolution takes place the the edges of the area a species inhabits and only a few individuals evolve, so it's hard to find graduation between successive species in the fossil record
organisms migrate as well as evolve as conditions become unfavourable and they need to search for better conditions, those who can't migrate die out
polar beards are in danger of becoming extinct due to the melting polar caps
Mass Extinction
vast number of species become extinct over a short period of time e.g. 250 million years ago 80% of marine invertebrates became extinct and 65 million years ago dinosaurs were wiped out
dinosaurs becuase the dominant species on Earth due to a great wave of adaptive radiation spanning 100 million years
Human Evolution
multiregional model: Homo erectus migrated out of Africa to Europe, Asia and Australia; these hominids evolved in parallel; in each area they evolved into Homo sapiens
out of Africa (monogenesis) model: each of the Homo species evolved in Africa then migrated out of Africa, replacing the other Homo species living in these new locations (Asia, Europe etc.). This is the theory held by most scientists
Human Evolution From Ape to Human
Name When found (mya) Features Cranial volume (cm3)
Australopethicus 2.5-3.5 walked on 2 legs 380-450
Homo habilis 1.5-2.5 made stone tools 750-800
Homo erectus 0.5-1.6 used fire, lived in groups 850
Homo sapiens since 0.3 hunter gatherers, buried their dead 1350
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