a

b

c

a

b

c

A B C

First niche dimension

Seco

nd n

iche d

imensi

on

Ecological niche concept: fundamental and realized niches

Avoiding competition; e.g., niche subdivision: honeyeater species

Anolis: subdividing space

Trends in biodiversity

Extinctions: opportunities for diversification

• 1. Background extinction– Normal; the experience for most species that have

existed.

• 2. Mass Extinctions = catastrophic– > 60% of extant species disappear within 1 million

years

Mass extinctions

End of Permian Extinction

54% marine families84% marine genera80-90% marine species

End of Permian Mass Extinction

• Cause of mass extinctions• Environmental change so enormous and sudden that an evolutionary

response is impossible.

• Smaller extinction events• Habitat destruction (prehistoric and historic) major cause• Lesser causes: introduced predators or disease; elevated interspecific

competition.• Little evidence that species shift geographic ranges as immediate

responses to deteriorating habitats, introduced predators or competitors.

• Reduction of population size also reduces the chance of adapting to the change .

– Genetic variation is reduced.

• Factors perhaps enhancing species extinction

• 1. Specialization

• 2. Geographic range

• 3. Population size

• K-T extinction • Evidence of a significant impact discovered, early 1980s• Iridium: rare on earth, common in asteroids & meteorites

Cretaceous / Tertiary boundary

95 localities

H: asteroid 10-15 km dia65 mya

• Critique of collision hypothesis (dinosaur extinction)– Effects short-lived (100s of years) – Dinosaur extinction (10,000 – 250,000 years)– Catastrophe was too selective.