Adaptive Radiations and Extinctions

Lecture 1

What is an Extinction

A permanent end of a species

What is the natural rate of extinctions

0.1-1 per million species per year

What percentage of species are now exticnt

99.9%

Why are fossil records important when considering extinction

they allow us to estimate species present before extinction and how they have evolved over time/changed

What causes extinctions/ why do they happen?

Slow decline and inbreeding

What changes in the environment influence extinction?

Biological, Climatic or Physical Changes

Caused by a multigenerational loss in _

fitness. this leads to habitat reduction and dissolution caused by competition

How do extictions lead to diversification in species?

They empty ecological niches allowing new species to fill them and undergo adaptive radiation

What is adaptive radiation?

Rapid evolution of many new species from a single ancestral species such as Jurrasic extinction led to radiation of modern corals

What is the difference between background and mass extinctions?

Background is slow and normal (easy to explain) whereas mass is fast and unpredictable

What factors do not determine extinctions

Genotype

Fertility

Age

What factors DO determine extinctions?

Geographic Dispersal

Rule 1 of the theory of adaptive radiations

Rapid diversification of organisms to exploit distinct available ecological niches

Rule 2 of the theory of adaptive radiations

Competition between different forms explotiting ecological niches leads to specialisation

Rule 3 of the theory of adaptive radiations

Specialisation leads to trade offs and itermediate phenotypes may be selected against

What are the 3 main causes of Adaptive radiations

1. Ecological Release

2. Ecological Opportunity

3. Key innovation/Major transition

What is a major transition?

Phenotypic innovation leading to accelerated evolutionary rates and radiation e.g. the evolution of the egg

Model system for adaptive radiation

Pseudomonia flourescens

Shaken Culture

• No ecological niches

• Environment is mixed

• No distinct microhabitats

• Only one phenotype - smooth

Static culture

• multiple ecological niches

• stratified

• 3 layers: oxygen rich top, moderate oxygen middle, low oxygen bottom

• these create different niches that the bacteria can exploit