Lecture 39 Extinction

Lecture 39—Extinction

This is the last lecture in the course and it is fitting that we consider the question of extinction. There are two kinds of extinction:

taxonomic extinction when one species through evolution becomes another: Homo erectus evolved to become H. sapiens in Africa and H. erectus is no more.

True extinction occurs when a line of decent dies out leaving no descendants behind. (e.g. Dodo bird).

Extinction can occur to any taxon, but it is common for species to become extinct but rare for higher taxonomic groups.

Species become extinct for any of these reasons:

Climate Changes

Food supply drops

Loss of habitat

Predation

Parasitism

Competition

Global catastrophe

What happens when the environment changes depends on

How fast the change is and the genetic potential of the species. When the change occurs these are the possibilities:

Migration--The species can migrate either by picking up and moving to a new environment or shifting ranges.

Evolution—If the change is slow enough and the genetic potential is great enough the species can evolve to survive in the new conditions.

Extinction—If migration and evolution are not possible, extinction is the result.

Extinction of one groups leaves an opening for the evolution of another group. (Extinction of the Dinosaurs opened up many niches for mammals).

Extinction happens to all taxa. The fact that extinction occurs argues against the Intelligent Design hypothesis because it is obvious that the extinct organism was not designed properly.

Mass Extinctions: Global die-off of many species. There have been at least 6 mass extinctions recorded in the geological record.There must have been another when the Oxygen Revolution occurred killing most anaerobic organisms but this happened over millions of years. There is another occurring right now as humans are causing directly or indirectly the death of many species, primarily by habitat destruction. Whenever humans enter a new habitat, they are mass killings of the large animals; this is best documented by the North American Giant Mammal extinction about 10,000 ya. Similar events occurred in Australia and New Zealand when humans arrived.

All of the geological mass extinction events appear to be caused at least in part by massive volcanic eruptions. The best known extinction is the K-T event which was triggered by an asteroid and led to final demise of the dinosaurs, ~65 mya.

4 lines of evidence for this hypothesis:

Iridium deposits

Impact crater off Yucatan, Mexico at right date

Impact deposits of tektites & quartz suggest high velocity impact at Yucatan

Pattern of extinction—sudden synchronous over the world

Terms/Concepts to Define:

Extinction

Taxonomic Extinction

Mass Extinction

K-T extinction

Nuclear winter

Overkill hypothesis

Anthropocene mass extinction

Amphioxus

Can you answer these questions?

1. The dinosaurs are long gone and yet many scientists say that they are not truly extinct. What do they mean and why would they say that?
2. Humans are causing the current mass extinction, what exactly are they doing that is causing the greatest harm? Please explain. Why is it that most animals will not be able to adapt?
3. What do you believe is the likelihood that humans will be able to survive another 100 years? What is the greatest threat to their existence?
4. The recent scientific data suggests that volcanoes are a major cause of most of the mass extinctions. Just how could volcanoes affect the entire globe and cause the death of massive numbers of organisms?
5. What is the Overkill Hypothesis and what is the evidence for it?
6. What was the result of the dinosaur extinction? Would those events have occurred if the dinosaurs had not become extinct?