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.
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