Biogeography and Macroevolution

Objectives

• Discuss the work of the Grants
• Compare/contrast allopatric and sympatric speciation
• Summarize how reptiles evolved

Biogeography is the study of how and why plants and animals live where they do. It provides evidence for evolution.

Biogeography of islands provides good evidence. Recall Darwin's observations at the Galapagos.

Adaptive radiation is the process by which a single species evolves into many new species to fill available niches.

In the 1970s Peter and Rosemary Grant went to the Galapagos Islands to observe the finches. There was a drought resulting in fewer seeds.

Birds with small beaks could only eat small seeds but birds with big beaks could eat any seed.

The Grants observed evolution by natural selection.

Origin of Species

Macroevolution is evolution above the level of species.

The process by which a new species evolves is speciation.

A species is a group of organisms that can breed and produce fertile offspring.

Allopatric Speciation

• Some members of a species become isolated
• They remain separated and evolve genetic differences
• They can no longer breed with original species
• Now a new species!

Sympatric Speciation

• No geographic isolation
• Reproductive isolation

When geological and climate conditions are stable, evolution may be gradual. (gradualism model) This is what Darwin thought.

When geological and climate conditions are changing, evolution may happen more quickly, following a punctuated equilibrium model.

The punctuated equilibrium model is better supported by the fossil record.

Reptiles

Earliest amniotes evolved ~350 million years ago. Resembled lizards and could live on land.

About 320 million years ago amniotes diverged into synapsids and sauropsids. The two groups had different skulls.

Synapsids eventually gave rise to mammals.

Sauropsids

• Reptiles
• Dinosaurs
• Birds

Dinosaurs

• Reptiles but not lizards
• Over 1,000 species
• Dominated Mesozoic Era

Some of the earliest reptiles to diverge were ancestors of turtles.