Extinction (Siva-Jothy)

Question 1

Types of Extinction

Answer 1

• Local Extinction
• Species Extinction
• Mass Extinction

Question 2

Local Extinction

Answer 2

Loss of a population from a particular area, e.g. wolves and bears lost from Britain

Question 3

Species Extinction

Answer 3

Loss of a species, e.g. Dodo and Great auk

Question 4

Mass Extinction

Answer 4

Period of geological time when extinction rate peaks. It is characterised by taxonomic breadth and geological brevity (e.g. 100,000 years).

99% of all species that have ever existed have gone extinct.

Question 5

Why do species go extinct?

Answer 5

• Racial Senescence?
• Competition from better adapted species?
• Environmental Change?

Question 6

Racial Senescence?

Answer 6

Reason species go extinct? NOT LIKELY

Species undergo a life cycle like an individual organism. Species created, vigorous youth, normal middle-age, gradually to senescence.
Orthogenesis: Evolution, once started, continues under its own momentum.

Question 7

Why is racial senescent unlikely to be the cause of extinction?

Answer 7

• No mechanisms known to produce orthogenesis
• Works against natural selection (which works to remove maladaptive traits, not what orthogenesis suggests, in which extinction is due to bad traits.
• Species don’t have an allotted lifespan
• No real evidence.

Question 8

Racial Senescence - Irish Elk?

Answer 8

Orthogenesis reasoning: Antlers grew too large and couldn’t be supported

Reasoning against ortheogenesis: Badly adapted to post ice-age forests

• They became extinct after the last ice age (very abruptly).
• They were very large animals, small SA:V, which is good for cold icy weather, not for post ice-age.

Question 9

Racial Senescence - Gryphea?

Answer 9

Orthogenesis reasoning: Originated from Ostrea
Hinge started to move so much, the animal because trapped inside and died.

Reasoning against ortheogenesis:

• No evidence it evolved from Ostrea.
• No evidence that coiling increased over time.
• Found that mud caused locking of shells - not hinges.
• The sudden changes in sea level and habitat structure caused extinction.

Question 10

Competition from better adapted species?

Answer 10

Reason species go extinct? YES

Species went extinct because of competition (or predation or disease) from better adapted species.
Reptiles aren’t very efficient, a lot of energy is required to keep muscles tort, even if they’re not moving.
Mammals’ weight is supported through their bone structure.
-True that better adapted species outcompete, meaning evolution is progressive.
-Could predict a prefect organism will eventually evolve and evolution will stop. However, this is impossible die to co-evolution.

Question 11

Co-evolution

Answer 11

The influence of closely associated species on each other in their evolution. (largest co-evolution = parasite and host).

Question 12

Red Queen Hypothesis

Answer 12

‘Red Queen Hypothesis’: “Have to run faster and faster in order to stay still”. Even in the absence of environmental change, species are continually evolving. All species have to evolve to keep up, otherwise things move forward too quickly and they’ll be left behind. Looks like nothing is happening because everything is continually evolving.

Question 13

Environmental Change?

Answer 13

Proposed Idea: Panama land bridge formed, N. American mammals (placental) moved down and outcompeted S. American mammals (marsupial), because they were more advanced.
Now believe: The competition was exacerbated by Andean rain shadow, making S. American mammals less well adapted than temperate N. American mammals, allowing placental to outcompete marsupials as they were more accustomed to the environment.

Question 14

Mass Extinction Events

Answer 14

1. Ordovican (marine invertebrates)
2. Denovian (marine invertebrates, fish)
3. Permian (marine invertebrates, trilobites, reptiles)
4. Triassic (marine invertebrates, reptiles, freshwater fish, insects).
5. Cretaceous (marine invertebrates, insects, marsupials, belemnites, plesiosaurs, masosaurs, pterosaurs, dinosaurs).

Question 15

Permian Extinction

Answer 15

Trilobites became extinct during this mass extinction.

• Climatic events drove trilobites to extinction.
• Land masses collided to form a ‘supercontinent’. Causing sea levels to drop. As trilobites lived in shallow waters, they were unable to survive in the deeper waters

Coastal areas have less extreme climate because temperature fluctuations are mediated by the sea. The more land mass, more heat is absorbed, temperature fluctuations are much larger. The organisms that became extinct were not well adapted to the dramatic climate changes.

Question 16

Cretaceous Extinction

Answer 16

Dinosaurs
Many explanations for why the dinosaurs went extinct did not explain why many marine invertebrates went extinct at the same time. (Evolution of angiosperms, mammals ate dinosaur eggs, sex determination, hot balls, too large to couplate).

Asteroid Impact
Asteroid hit Earth, kicked dust into the atmosphere, dust obscured the sun. All plants died, although seeds survived. There was no food for dinosaurs, so they eventually became extinct.
-Iridium was found as evidence for the asteroid hitting Earth. Layers of a black band were formed at the KT boundary. Tested to be iridium which is common in asteroid and meteoroids.