Speciation Notes

Biological Species Concept

Two organisms belong to the same species IF:1) They can mate2) And produce living and fertile offspring

When it comes to species, appearance isn’t everything!

The Western meadowlark (left) and the Eastern meadowlark (right)appear to be identical, and their ranges overlap, but their distinct songs prevent interbreeding. They are considered to be different species.

Arrowhead Plants

Grows on Land

Grows in Water

Arrowhead plants look different, but can interbreed so they are of the same species.

Key Idea: BSC depends on reproductive isolation.

Problem: How do we classify organisms we cannot observe carrying out sexual reproduction?

Additional Ways to Define SpeciesIt can be difficult to group all organisms based

on their ability to reproduce, so scientists also consider morphology (physical characteristics) , ecological role, and genetic history.

Remember the concept of a “species” is made up by humans to organize life. Organisms don’t always neatly fall into our categories.

• Key Idea: New species evolve when populations become reproductively isolated from each other.

• Reproductive Isolation- Barriers to reproduction that prevent organisms from mating or producing living and fertile offspring.