Lecture 15 - biogeography & biodiversity

Biogeography

The study of where organisms live and why they live there.

What 3 processes change species ranges?

1. Variance

   • A physical barrier that splits one population into two.

2. Dispersal

   • Organisms move into new areas beyond their original range.

3. Extinction

• When a species or population disappears from part of its range.

Biodiversity

The variety of species and how they’re related. 

• Diversification rate: how fast species increase or decrease in a group over time.

  • R = speciation rate - extinction rate

Adaptive radiation

Rapid diversification of a single ancestral lineage into new species to fill empty ecological niches.

Direct competition

One group outcompetes another.

Incumbent replacement

When one group disappears, another group takes over its niche. Example: when dinosaurs went extinct, mammals diversified rapidly because of the open ecological space.

What are the 2 hypotheses explaining global diversity differences.

1. Positive feedback hypothesis

   • More species = more interaction → faster speciation

2. Time-for-speciation hypothesis

   • Older habitats have existed longer → more time for species to evolve.

Mosaic evolution

Different body parts evolve at different rates within the same species. This results in a mix of fast and slow evolving traits.

Gradual vs punctuated equilibrium

1. Gradualism

   • Evolution happens slowly and continuously over long periods. Small genetic changes accumulate leading to big differences over time.

2. Punctuated equilibrium

   • Species remain mostly unchanged (static) for long periods. Then, rapid burst of change occur during speciation events.

Micro vs Macro evolution

1. Microevolution: small scale evolutionary changes.

2. Macroevolution: large scale patterns (microevolution + time).