Biodiversity and Extinction

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

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

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

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

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

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

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

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

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

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

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

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