a b c a b c A B C First niche dimension Second niche dimension 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 families 84% marine genera 80-90% 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 km dia 65 mya

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