Extinction and speciation Describe the environmental changes that can cause extinction and evaluate the theories for extinction of the dinosaur Explain how some species become isolated Explain that speciation results when selection in isolated populations results in populations becoming so different they can no longer interbreed.

Human civilization, dates entirely within the Holocene. http://www.bbc.co.uk/nature/history_of_the_earth Human civilization, dates entirely within the Holocene. It’s this time period from when humans have had a significant impact on the Earth's climate and ecosystems to the present. The climate and environment on Earth is always changing These are the main causes of extinction, animals are not able to adapt quickly enough to the change in their environment Scroll down the page to see images of the geologic timeline Click on a few of the geological time periods (incl. The holocene) - Scrolling down the individual pages will tell you what species of animal lived during the time period and any other info Scroll further and mention the 5 big extinction events Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous Click on the link to David attenborough’s ‘tree of life series’ – 5min video.

Evolution of the earth: ice ages http://www.bbc.co.uk/nature/history_of_the_earth/Cryogenian#p00cgy7m http://www.bbc.co.uk/nature/history_of_the_earth/Cryogenian#p00cgym0 Both videos discuss the snowball earth theory – the last ice age and its retreat

Again, the major eras, showing approx Again, the major eras, showing approx. where the 5 big extinctions occurred (including the one for the dinosaurs further discussed on the following slides) Cambrian is famed for its explosion of abundant and diverse life forms.

Hypothesis: Extinction of the dinosaurs 65 million years ago, a large meteor hit the earth The impact caused a large amount of debris to go into the atmosphere. This blocked the light and heat of the sun, causing the earth to cool: an ICE AGE There have been many different ideas put forward to explain why the dinosuars died out. The two most likely are that their habitat slowly changed, and that a meteor impact triggered their extinction. Gradualist theory The gradualist hypothesis points to declines in the numbers and diversity of different groups of land and marine animals. - extinction due to climate change. The climate at the end of the Cretaceous was cooling - and a fall in sea level reduced dinosaur and shallow water marine animal habitats. Impact theory - good geophysical evidence for the occurrence of an asteroid impact at the end of the Cretaceous. A band of clay rich in the mineral iridium was deposited at the end of the Cretaceous and has been found at many places in the world. This mineral is rare on Earth but more common in meteorites. It has been suggested that the impact would have triggered a nuclear winter scenario that would have caused the death of the dinosaurs as well as the pterosaurs, several families of birds and mammals and also marine animals such as the plesiosaurs and ammonites.

The Chicxulub crater in Mexico

Other causes of speciation and extinction Predators: new predator comes to an area and wipes out a lesser species Diseases: microorganisms can infect a species, killing it e.g. Tazmanian Devil & cancer Competition: a mutation gives one species and advantage, causing the other to be unable to keep up Isolation: A population may be separated by geographical barriers e.g. on an island or on either side of a newly-formed mountain

DEFINITION OF A SPECIES A species is a group of organisms with similar features which can interbreed to produce fertile offspring Speciation (the origin of species) is the formation of new species from existing ones Through interbreeding, gene flow occurs between the populations of a species but not between populations of different species For populations to become different species, there must be some kind of barrier which prevents gene flow between them so that they become reproductively isolated. A barrier that prevents gene flow between populations is called an Isolating Mechanism and several mechanisms have been described as the means by which new species are created

The Galapagos islands, visited by Charles Darwin in 1835, are a group of volcanic islands situated 600 miles west of Ecuador Various species of animals came across the sea to inhabit these islands where they encountered little competition For example: All of the Galapagos finches are believed to be descended from a type of mainland finch that invaded the islands They are all so different now that are are unable to breed with the other island finches.

Fourteen species of finch now inhabit the various islands differing considerably from one another with respect to their beak shapes and feeding habits

SPECIATION Reproductive isolation of an organism due to separation from other, similar organisms A population of any organism shows genetic variation. When isolated from the original population, the new group must face different environmental pressures. Some organisms have alleles for certain genes which gives them an advantage over the other These organisms survive better in the new conditions and pass on these genes to their offspring. Over several generations, they are no longer able to breed with the original species as they are so different. They are an endemic organism: An organism that has evolved in only one place, in geographical isolation.

Extinction and speciation - review Describe the environmental changes that can cause extinction and evaluate the theories for extinction of the dinosaur Explain how some species become isolated Explain that speciation results when selection in isolated populations results in populations becoming so different they can no longer interbreed. Homework: Make a list of the key terms from chapter 6 and their definitions